ELECTROMAGNETIC WAVE DETECTOR AND ELECTROMAGNETIC WAVE DETECTOR ARRAY

An electromagnetic wave detector includes a semiconductor layer, a two-dimensional material layer, a first electrode portion, a second electrode portion, and a ferroelectric layer. Two-dimensional material layer is electrically connected to semiconductor layer. First electrode portion is electrically connected to two-dimensional material layer. Second electrode portion is electrically connected to two-dimensional material layer with semiconductor layer interposed therebetween. Ferroelectric layer is electrically connected to at least any one of first electrode portion, second electrode portion and semiconductor layer. Electromagnetic wave detector is configured such that an electric field generated from ferroelectric layer is shielded with respect to two-dimensional material layer. Alternatively, ferroelectric layer is arranged so as not to be overlapped with two-dimensional material layer in plan view.

TECHNICAL FIELD

The present disclosure relates to an electromagnetic wave detector and an electromagnetic wave detector array.

BACKGROUND ART

As a material of an electromagnetic wave detecting layer for use in a next-generation electromagnetic wave detector, graphene which is one example of a two-dimensional material layer is known. Graphene has very high mobility. Absorptance of graphene is as low as 2.3%. For this reason, a technique of enhancing the sensitivity in an electromagnetic wave detector in which graphene is used as a two-dimensional material layer has been proposed.

For example, U.S. Patent Application Publication 2015/0243826 (PTL 1) proposes a detector having the following structure. That, in U.S. Patent Application Publication 2015/0243826, two or more dielectric layers are disposed on the n-type semiconductor layer. A graphene layer is formed on two dielectric layers, and on a surface part of an n-type semiconductor layer located between the two dielectric layers. Source and drain electrodes connected to both ends of the graphene layer are arranged on the dielectric layer. The gate electrode is connected to the n-type semiconductor layer.

In the aforementioned detector, voltage is applied to the graphene layer serving as a channel via the source and drain electrodes. As a result, the photo carrier generated in the n-type semiconductor layer is amplified, and thus the sensitivity of the detector improves. When voltage is applied to the gate electrode, and the source electrode or the drain electrode, OFF operation is enabled by Schottky connection between graphene and the n-type semiconductor layer.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

In the detector described in the above publication (electromagnetic wave detector), an electromagnetic wave is detected by a photo carrier generated by application of the electromagnetic wave to the semiconductor layer. Therefore, the sensitivity of the detector depends on the quantum efficiency of the semiconductor layer. The quantum efficiency of the semiconductor layer is not sufficiently high depending on the wavelength of the electromagnetic wave. Therefore, the detection sensitivity of the electromagnetic wave detector is insufficient.

The present disclosure was made in light of the above problems, and it is an object of the present disclosure to provide an electromagnetic wave detector and an electromagnetic wave detector array capable of improving the sensitivity.

Solution to Problem

An electromagnetic wave detector of the present disclosure includes a semiconductor layer, a two-dimensional material layer, a first electrode portion, a second electrode portion, and a ferroelectric layer. The two-dimensional material layer is electrically connected to the semiconductor layer. The first electrode portion is electrically connected to the two-dimensional material layer. The second electrode portion is electrically connected to the two-dimensional material layer with the semiconductor layer interposed therebetween. The ferroelectric layer is electrically connected to at least any one of the first electrode portion, the second electrode portion, and the semiconductor layer. The electromagnetic wave detector is configured such that the electric field generated from the ferroelectric layer is shielded with respect to the two-dimensional material layer. Alternatively, the ferroelectric layer is arranged so as not to be overlapped with the two-dimensional material layer in plan view.

Advantageous Effects of Invention

According to the electromagnetic wave detector of the present disclosure, the ferroelectric layer is electrically connected to at least any one of the first electrode portion, the second electrode portion, and the semiconductor layer. The pyroelectric effect of the ferroelectric layer does not depend on the wavelength of the electromagnetic wave. Therefore, the sensitivity of the electromagnetic wave detector does not depend on the quantum efficiency of the semiconductor layer. Therefore, even for a wavelength for which the quantum efficiency of the semiconductor layer decreases, deterioration in sensitivity of the electromagnetic wave detector is suppressed. Therefore, the sensitivity of the electromagnetic wave detector improves.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments are described with reference to the drawings. In the following, the same or the corresponding part is denoted by the same reference numeral and overlapping description is not repeated.

In the embodiments described below, the drawings are schematic, and conceptually illustrate the functions or structures. The embodiments described below will not restrict the present disclosure. The basic structure of the electromagnetic wave detector is common among all of the embodiments unless otherwise noted. The one denoted by the same reference numeral corresponds to the same object or a corresponding object as described above. This applies in the entirety of the description.

In the embodiments described below, configuration of an electromagnetic wave detector in the case of detecting visible light or infrared light is described, however, the light to be detected by the electromagnetic wave detector of the present disclosure is not limited to visible light and infrared light. The embodiments described below are effective as detectors that detect, for example, X-ray, ultraviolet light, far red light, terahertz (THz) wave, radio waves such as microwave, as well as visible light and infrared light. In the embodiments of the present disclosure, these light and radio waves are collectively referred to as an electromagnetic wave.

Also, in the present embodiments, graphene can be described by the terms of p-type graphene and n-type graphene. In the following embodiments, the graphene having more holes than intrinsic graphene is called p-type graphene, and the graphene having more electrons than intrinsic graphene is called n-type graphene. That is, the n-type material is a material having electron-donating nature. Also, the p-type material is a material having electron-withdrawing nature.

Also, when polarization is observed in electric charges in the entire molecule, the one in which electrons are dominant is sometimes called n-type. When polarization is observed in electric charges in the entire molecule, the one in which holes are dominant is sometimes called p-type. As a material of the member that comes into contact with graphene which is one example of the two-dimensional material layer, one of an organic substance or an inorganic substance, or a mixture of an organic substance and an inorganic substance may be used.

Regarding plasmon resonance phenomena such as a surface plasmon resonance phenomenon that is the interaction between the metal surface and the light, a phenomenon called a pseudo surface plasmon resonance phenomenon in the meaning of resonance concerning metal surface outside the visible light range and near-infrared range, or a phenomenon called a metamaterial or a plasmonic metamaterial in the meaning of manipulating the wavelength by a structure having a dimension of less than or equal to the wavelength, these are not particularly distinguished from each other according to the names, but are equally handled from the aspect the effect exerted by the phenomenon. Here, these resonances are called, surface plasmon resonance, plasmon resonance, or simply resonance.

In the embodiments described below, description is made for graphene as an example of a material of the two-dimensional material layer, however, the material of the two-dimensional material layer is not limited to graphene. For example, as a material of the two-dimensional material layer, materials such as transition metal dichalcogenide (TMD), black phosphorus, silicene (two-dimensional honeycomb structure by silicon atoms), genmanene (two-dimensional honeycomb structure by germanium atoms) and the like are applicable. Examples of transition metal dichalcogenide include transition metal dichalcogenide such as molybdenum disulfide (MoS2), tungsten disulfide (WS2), tungsten diselenide (WSe2) and the like.

More preferably, the two-dimensional material layer contains any one of materials selected from the group consisting of graphene, transition metal dichalcogenide (TMD), black phosphorus, silicene (two-dimensional honeycomb structure by silicon atoms), graphene nanoribbon, and borophene.

These materials have structures similar to those of graphene. In these materials, atoms are arranged by a monolayer in the two-dimensional surface. Therefore, when these materials are applied to the two-dimensional material layer, the operation and effect similar to those in the case of applying graphene to the two-dimensional material layer are obtained.

In the present embodiments, the object represented by insulating layer is a layer of an insulator having such a thickness that will not generate a tunnel current.

<Configuration of Electromagnetic Wave Detector100>

Referring toFIGS.1to6, a configuration of an electromagnetic wave detector100according to Embodiment 1 is described.FIG.1is a section view in the 1-1 line ofFIG.2.

As shown inFIG.1, electromagnetic wave detector100includes a semiconductor layer4, a two-dimensional material layer1, a first electrode portion2a, a second electrode portion2b, and a ferroelectric layer5. Two-dimensional material layer1, first electrode portion2a, second electrode portion2band semiconductor layer4are electrically connected in the order of first electrode portion2a, two-dimensional material layer1, semiconductor layer4and second electrode portion2b. In the present embodiment, electromagnetic wave detector100further includes an insulating film3. Also, electromagnetic wave detector100further includes at least one of a voltmeter VM and a later-described ammeter IM (seeFIG.5). Electromagnetic wave detector100shown inFIG.1further includes voltmeter VM.

As shown inFIG.1, semiconductor layer4has a first surface4aand a second surface4b. Second surface4bis opposed to first surface4a. Two-dimensional material layer1, first electrode portion2a, insulating film3and ferroelectric layer5are arranged on first surface4aside. Second electrode portion2bis arranged on second surface4bside. First surface4aside is called a top surface side. Second surface4bside is called a bottom surface side.

Two-dimensional material layer1is electrically connected to semiconductor layer4. Two-dimensional material layer1is arranged on first electrode portion2a, insulating film3and semiconductor layer4. That is, two-dimensional material layer1is in contact with first electrode portion2a, insulating film3and semiconductor layer4.

Two-dimensional material layer1includes a first part1a, a second part1band a third part1c. First part1ais arranged on semiconductor layer4. First part1ais electrically connected to semiconductor layer4. Second part1bis arranged on first electrode portion2a. Second part1bis electrically connected to first electrode portion2a. Third part1cis electrically connected to first part1aand second part1b. First part1aand second part1bare connected by third part1c. In the present embodiment, third part1cis arranged on insulating film3.

Thicknesses of first part1a, second part1band third part1cmay be mutually the same. Along the direction in which two-dimensional material layer1is overlaid on semiconductor layer4, a distance between the surface of the top surface side of first part1aand first surface4aof semiconductor layer4is smaller than a distance between the surface of the top surface side of second part1band first surface4aof semiconductor layer4. Although not illustrated, on the surface of two-dimensional material layer1, projections and recesses caused by first part1a, second part1band third part1care formed.

First electrode portion2ais electrically connected to two-dimensional material layer1. First electrode portion2ais electrically connected to two-dimensional material layer1without being interposed by semiconductor layer4. In the present embodiment, first electrode portion2ais directly connected to two-dimensional material layer1. First electrode portion2ais arranged on the bottom surface side of two-dimensional material layer1. Although not illustrated, first electrode portion2amay be arranged on the top surface side of two-dimensional material layer1.

Second electrode portion2bis electrically connected to two-dimensional material layer1with semiconductor layer4interposed therebetween. Second electrode portion2bis in contact with semiconductor layer4. In electromagnetic wave detector100shown inFIG.1, second electrode portion2bcovers the entire surface of second surface4bof semiconductor layer4. Electromagnetic wave detector100in which second electrode portion2bcovers the entire surface of second surface4bis suited for the case where an electromagnetic wave that is to be detected enters electromagnetic wave detector100only from first surface4aside (top surface side). Also, the electromagnetic wave having entered electromagnetic wave detector100from first surface4aside (top surface side) penetrates ferroelectric layer5and semiconductor layer4, and is then reflected by second electrode portion2b. The electromagnetic wave reflected by second electrode portion2bagain enters ferroelectric layer5from second surface4bside (bottom surface side). Therefore, the electromagnetic wave enters ferroelectric layer5from each of first surface4aside and second surface4bside. As a result, the absorptivity of electromagnetic wave of ferroelectric layer5improves.

Although not illustrated, second electrode portion2bneed not cover the entire surface of semiconductor layer4. That is, it is only required that second electrode portion2bis in contact with part of semiconductor layer4. For example, it is only required that second electrode portion2bis in contact with part of any one of first surface4a, second surface4band a side surface extending in the direction intersecting with first surface4aand second surface4b. When second surface4bof semiconductor layer4is exposed from second electrode portion2b, electromagnetic wave detector100is capable of detecting the electromagnetic wave entered from second surface4bside.

Insulating film3is arranged on semiconductor layer4. Insulating film3is arranged on a top surface side of semiconductor layer4. In insulating film3, an opening OP is formed. Opening OP penetrates insulating film3. Semiconductor layer4is exposed from insulating film3in opening OP. That is, semiconductor layer4is not covered by insulating film3in opening OP. First surface4aof semiconductor layer4is not covered by insulating film3in opening OP.

Two-dimensional material layer1is electrically connected to semiconductor layer4in opening OP. Two-dimensional material layer1extends from above opening OP to insulating film3. In the present embodiment, two-dimensional material layer1extends from above opening OP to above insulating film3. First part1aof two-dimensional material layer1is arranged on first surface4aof semiconductor layer4in opening OP. Preferably, two-dimensional material layer1is joined with semiconductor layer4by Schottky junction in opening OP. First part1aof two-dimensional material layer1is joined with semiconductor layer4in opening OP. Insulating film3separates second part1band third part1cof two-dimensional material layer1from semiconductor layer4.

A first end of two-dimensional material layer1is arranged in opening OP. A second end of two-dimensional material layer1is arranged on second electrode portion2b. The first end and the second end of two-dimensional material layer1are end parts in the longitudinal direction of two-dimensional material layer1. InFIG.1, the first end of two-dimensional material layer1is arranged on an opposite side of first electrode portion2awith respect to the center of opening OP in the in-plane direction of semiconductor layer4, and the second end of two-dimensional material layer1is arranged on first electrode portion2aside with respect to the center of opening OP. Although not illustrated, each of the first end and the second end of two-dimensional material layer1may be arranged on first electrode portion2aside with respect to the center of opening OP.

Also, inFIG.1, two-dimensional material layer1is arranged such that part of first surface4aof semiconductor layer4is exposed in opening OP. Although not illustrated, two-dimensional material layer1may be arranged to cover the entire surface of first surface4aof semiconductor layer4.

Insulating film3has a third surface3aand a fourth surface3b. Third surface3ais in contact with first surface4aof semiconductor layer4. Fourth surface3bis opposed to third surface3a. At least part of fourth surface3bis in contact with two-dimensional material layer1. That is, insulating film3is arranged on the bottom surface side with respect to two-dimensional material layer1. First electrode portion2ais arranged on fourth surface3bof insulating film3. First electrode portion2ais arranged at a position distanced from opening OP.

Ferroelectric layer5is electrically connected to at least any one of first electrode portion2a, second electrode portion2band semiconductor layer4. In the present embodiment, ferroelectric layer5is electrically connected to first electrode portion2a, second electrode portion2band semiconductor layer4. InFIG.1, insulating film3is arranged on ferroelectric layer5. That is, ferroelectric layer5is covered by insulating film3. Ferroelectric layer5is arranged on semiconductor layer4. Ferroelectric layer5is in contact with semiconductor layer4. Ferroelectric layer5is arranged between first electrode portion2aand semiconductor layer4.

Ferroelectric layer5has sensitivity for a wavelength of electromagnetic wave (detection wavelength) that is an object to be detected by electromagnetic wave detector100. Therefore, when an electromagnetic wave having a detection wavelength is applied to ferroelectric layer5, polarization changes in ferroelectric layer5. In other words, when an electromagnetic wave having a detection wavelength is applied to ferroelectric layer5, pyroelectric effect is generated in ferroelectric layer5. The direction in which polarization changes (polarization direction) is preferably the direction in which a photo carrier generated by polarization is injected into two-dimensional material layer1. In the present embodiment, the direction in which an electromagnetic wave is applied to electromagnetic wave detector100is a direction in which first electrode portion2aand second electrode portion2boverlap (vertical direction on the paper surface).

In the present embodiment, ferroelectric layer5is arranged such that resistance between first electrode portion2aand second electrode portion2bchanges when polarization in ferroelectric layer5changes. As a result, the electric field is generated along the direction in which first electrode portion2aand second electrode portion2boverlap (vertical direction on the paper surface).

Ferroelectric layer5is configured to inject a photo carrier generated in ferroelectric layer5into two-dimensional material layer1. The wording “a photo carrier is injected into two-dimensional material layer1” means that a photo carrier is injected into two-dimensional material layer1without being mediated by insulating film3. The photo carrier generated from ferroelectric layer5is injected into two-dimensional material layer1through at least any one of first electrode portion2a, second electrode portion2band semiconductor layer4.

Preferably, ferroelectric layer5is arranged such that voltage in a forward bias direction is applied to two-dimensional material layer1and semiconductor layer4. For example, when a p-type material is used in semiconductor layer4, and an n-type material is used in the two-dimensional material layer, it is preferred that ferroelectric layer5is arranged such that holes are injected into first electrode portion2afrom ferroelectric layer5and electrons are injected into second electrode portion2bfrom ferroelectric layer5by application of an electromagnetic wave. When an n-type material is used in semiconductor layer4, and a p-type material is used in the two-dimensional material layer, it is preferred that ferroelectric layer5is arranged such that electrons are injected into first electrode portion2afrom ferroelectric layer5and holes are injected into second electrode portion2bfrom ferroelectric layer5by application of an electromagnetic wave.

Ferroelectric layer5may be arranged such that voltage in a reverse bias direction is applied to two-dimensional material layer1and semiconductor layer4. In this case, when reverse bias is applied, application of electromagnetic wave switches between the saturation region and the breakdown region of semiconductor layer4, and thus the dark current is reduced.

Electromagnetic wave detector100is configured such that the electric field generated from ferroelectric layer5is shielded with respect to two-dimensional material layer1. Alternatively, ferroelectric layer5is arranged so as not to be overlapped with two-dimensional material layer1in plan view.

In Embodiment 1, electromagnetic wave detector100is configured such that the electric field generated from ferroelectric layer5is shielded with respect to two-dimensional material layer1. The electric field is shielded by a conductor.

Therefore, the electric field generated by ferroelectric layer5is shielded by at least any one of first electrode portion2a, second electrode portion2band semiconductor layer4.

A part of ferroelectric layer5facing with two-dimensional material layer1, and two-dimensional material layer1sandwich at least any one of first electrode portion2a, second electrode portion2band semiconductor layer4. Preferably, between the entire surface of a part of ferroelectric layer5facing with two-dimensional material layer1, and two-dimensional material layer1, at least any one of first electrode portion2a, second electrode portion2band semiconductor layer4is sandwiched. In electromagnetic wave detector100shown inFIG.1, a part of ferroelectric layer5facing with two-dimensional material layer1, and two-dimensional material layer1sandwich first electrode portion2a. Therefore, the electric field generated by ferroelectric layer5is shielded by first electrode portion2a.

Preferably, ferroelectric layer5is not in contact with two-dimensional material layer1. Contact resistance between two-dimensional material layer1and ferroelectric layer5is large. Therefore, if two-dimensional material layer1and ferroelectric layer5come into contact with each other, the electric field generated by change in polarization of ferroelectric layer5significantly changes the Fermi level of two-dimensional material layer1, which may result in change in characteristics of electromagnetic wave detector100.

The case where ferroelectric layer5is arranged so as not to be overlapped with two-dimensional material layer1in plan view is described in Embodiment 2.

Voltmeter VM is electrically connected between first electrode portion2aand second electrode portion2b. Voltmeter VM is voltmeter VM for detecting change in voltage generated by application of an electromagnetic wave to electromagnetic wave detector100. Electromagnetic wave detector100is configured to detect an electromagnetic wave by detecting change in voltage of a current flowing between first electrode portion2aand second electrode portion2bby voltmeter VM.

As shown inFIG.2, the shape in plan view of an end part of two-dimensional material layer1is a rectangular shape. The shape of an end part of two-dimensional material layer1is not limited to a rectangular shape, and may be a triangular shape, a comb shape and the like. Although not illustrated, when the shape of an end part of two-dimensional material layer1is a comb shape, first part1amay have a plurality of end parts that are electrically connected to a semiconductor. InFIG.2, the entire end part of two-dimensional material layer1is in contact with semiconductor layer4. Therefore, the entire end part of two-dimensional material layer1is configured as first part1a. Although not illustrated, a part of an end part of two-dimensional material layer1may be in contact with semiconductor layer4, and the other part of an end part of two-dimensional material layer1may be in contact with insulating film3. That is, a part of an end part of two-dimensional material layer1may be configured as first part1a, and the other part of an end part of two-dimensional material layer1may be configured as third part c.

As shown inFIG.3, ferroelectric layer5may be arranged on second electrode portion2b. Ferroelectric layer5is sandwiched between second electrode portion2band semiconductor layer4. A part of ferroelectric layer5facing with two-dimensional material layer1, and two-dimensional material layer1sandwich semiconductor layer4. Therefore, the electric field generated by ferroelectric layer5is shielded by semiconductor layer4. When the electric field is shielded by semiconductor layer4, it is desired that semiconductor layer4has high concentration. Also, when the electric field is shielded by semiconductor layer4, it is desired that semiconductor layer4has high conductivity. Also, when the electric field is shielded by semiconductor layer4, it is desired that semiconductor layer4has large thickness.

As shown inFIG.4, ferroelectric layer5may be directly connected to two-dimensional material layer1on the side opposite to two-dimensional material layer1with respect to first electrode portion2a. A part of ferroelectric layer5facing with two-dimensional material layer1, and two-dimensional material layer1sandwich first electrode portion2a. The electric field generated by ferroelectric layer5is shielded by first electrode portion2a.

As shown inFIG.5, electromagnetic wave detector100may further include ammeter IM. Ammeter IM is electrically connected between first electrode portion2aand second electrode portion2b. Ammeter IM is ammeter IM for detecting change in current generated by application of an electromagnetic wave to electromagnetic wave detector100. Electromagnetic wave detector100is configured to detect an electromagnetic wave by detecting change in current flowing between first electrode portion2aand second electrode portion2bby ammeter IM.

As shown inFIG.6, electromagnetic wave detector100may further include a power source PW. Power source PW is electrically connected to first electrode portion2aand second electrode portion2b. Power source PW is configured to apply voltage V1to first electrode portion2aand second electrode portion2b. As a result, current I1flows between first electrode portion2aand second electrode portion2b.

Two-dimensional material layer1is, for example, monolayer graphene. Monolayer graphene is a monoatomic layer of two-dimensional carbon crystal. Graphene has a plurality of carbon atoms that are arranged in each of a plurality of chains arranged in a hexagonal form. Absorptance of graphene is as low as 2.3%. Specifically, absorptance of white light of graphene is 2.3%. In the present embodiment, the white light is light in which light having visible light wavelengths are evenly mixed. Two-dimensional material layer1may be multilayer graphene in which a plurality of graphene layers are laminated. The orientations of lattice vector of hexagonal lattices of graphene in multilayer graphene may be coincident or different from each other. The orientations of lattice vector of hexagonal lattices of graphene in multilayer graphene may be perfectly coincident. Two-dimensional material layer1may be graphene doped with a p-type or n-type impurity.

For example, by lamination of two or more layers of graphene layers, a band gap is formed in two-dimensional material layer1. In other words, by varying the number of multilayer graphene layers, it is possible to adjust the size of the band gap. As a result, two-dimensional material layer1is capable of having a wavelength selective effect that selects an electromagnetic wave (detection wavelength) that is a target for photoelectric conversion. Also, for example, as the number of graphene layers of multilayer graphene increases, the mobility in the channel region deteriorates. On the other hand, as the number of graphene layers of multilayer graphene increases, the influence of photo carrier scattering from the substrate is suppressed, so that the noise of electromagnetic wave detector100decreases. Therefore, in electromagnetic wave detector100having two-dimensional material layer1in which multilayer graphene is used, light absorption is increased, and hence the detection sensitivity of electromagnetic wave improves.

As two-dimensional material layer1, nanoribbon-like graphene (graphene nanoribbon) may be used. Two-dimensional material layer1may be sole graphene nanoribbon. The structure of two-dimensional material layer1may be such a structure that a plurality of graphene nanoribbons are laminated. The structure of two-dimensional material layer1may be such a structure that graphene nanoribbons are periodically arranged on a plane. In the case where two-dimensional material layer1has such a structure that graphene nanoribbons are periodically arranged, plasmon resonance is generated in the graphene nanoribbons, and hence the sensitivity of electromagnetic wave detector100improves. The structure in which graphene nanoribbons are periodically arranged is also called graphene metamaterial. In other words, the above-described effect is obtained in electromagnetic wave detector100in which graphene metamaterial is used as two-dimensional material layer1.

An end part of two-dimensional material layer1may be graphene nanoribbon. In this case, Schottky junction is formed in the joining region between graphene nanoribbon and the semiconductor part because the graphene nanoribbon has a bandgap.

By contact of second part1bof two-dimensional material layer1with first electrode portion2a, the photo carrier is doped from first electrode portion2ato two-dimensional material layer1. For example, when two-dimensional material layer1is graphene, and first electrode portion2ais gold (Au), the photo carrier is a hole. By the difference between the work function of graphene and the work function of gold (Au), holes are doped to second part1bthat is in contact with first electrode portion2a. When electromagnetic wave detector100operates in an electron conductive state while second part1bis doped with holes, the mobility of electrons flowing in the channel deteriorates by the influence of the holes. Therefore, the contact resistance between two-dimensional material layer1and first electrode portion2aincreases. In particular, when all regions in two-dimensional material layer1are formed of monolayer graphene, the amount of photo carrier (dope amount) introduced from first electrode portion2ainto two-dimensional material layer1is large. Therefore, deterioration in mobility of the field effect of electromagnetic wave detector100is significant. Therefore, when all regions of two-dimensional material layer1are formed of monolayer graphene, the performance of electromagnetic wave detector100deteriorates.

Also, the amount of photo carrier doped to multilayer graphene from first electrode portion2ais smaller than the amount of photo carrier doped to monolayer graphene from first electrode portion2a. Therefore, since first part1aand second part1bwhere the photo carrier is easy to be doped are formed of multilayer graphene, it is possible to suppress the increase in the contact resistance between two-dimensional material layer1and first electrode portion2a. This makes it possible to suppress the deterioration in mobility of the field effect of electromagnetic wave detector100, and thus it is possible to improve the performance of electromagnetic wave detector100.

<Configurations of First Electrode Portion2aand Second Electrode Portion2b>

Materials of first electrode portion2aand second electrode portion2bmay be any materials as long as they are conductors. Materials of first electrode portion2aand second electrode portion2bmay contain at least any one of, for example, gold (Au), silver (Ag), copper (Cu), aluminum (Al), nickel (Ni), chromium (Cr) and palladium (Pd). An unillustrated close adherence layer may be provided between first electrode portion2aand insulating film3, or between second electrode portion2band semiconductor layer4. The close adherence layer is formed to enhance the adherence. The material of close adherence layer includes, for example, metal materials such as chromium (Cr) or titanium (Ti).

A material of insulating film3is, for example, silicon oxide (SiO2). The material of insulating film3is not limited to silicon oxide, and may be, for example, tetraethyl orthosilicate (Si(OC2H5)4), silicon nitride (Si3N4), hafnium oxide (HfO2), aluminum oxide (Al2O3), nickel oxide (NiO), boron nitride (BN) (boron nitride), and siloxane-based polymer materials. For example, the atomic arrangement of boron nitride (BN) resembles the atomic arrangement of graphene. Therefore, when boron nitride (BN) comes into contact with two-dimensional material layer1formed of graphene, deterioration in electron mobility of two-dimensional material layer1is suppressed. Therefore, boron nitride (BN) is suited for an insulating film3as an underlying film arranged under two-dimensional material layer1.

Thickness of insulating film3is not particularly limited as long as first electrode portion2ais electrically insulated with respect to semiconductor layer4, and tunnel current is not generated between first electrode portion2aand semiconductor layer4. An insulating layer need not be arranged below two-dimensional material layer1.

A material of semiconductor layer4is, for example, a semiconductor material such as silicon (Si). Specifically, semiconductor layer4is, for example, a silicon substrate doped with impurities.

Semiconductor layer4may have a multilayer structure. Also, semiconductor layer4may be a pn-junction photodiode, a pin photodiode, a Schottky photodiode, or an avalanche photodiode. Also, semiconductor layer4may be a photo transistor.

In the present embodiment, while description is made for the case where the material constituting semiconductor layer4is a silicon substrate, the material of semiconductor layer4may be other material. Examples of materials of semiconductor layer4include silicon (Si), germanium (Ge), compound semiconductors such as group III-V semiconductors or group II-V semiconductors, cadmium mercury telluride (HgCdTe), iridium antimonide (InSb), lead selenide (PbSe), lead sulfide (PbS), cadmium sulfide (CdS), gallium nitride (GaN), silicon carbide (SiC), gallium phosphide (GaP), indium gallium arsenide (InGaAs), indium arsenide and (InAs). Semiconductor layer4may be a substrate including a quantum well or a quantum dot. The material of semiconductor layer4may be Type II superlattice. The material of semiconductor layer4may be a single material of the aforementioned materials, or may be a combination of the aforementioned materials.

It is desired that semiconductor layer4is doped with an impurity so that the resistivity is less than or equal to 100 Ω·cm. The readout speed (migration speed) of photo carrier in semiconductor layer4improves by doping semiconductor layer4at high concentration, and hence the response speed of electromagnetic wave detector100improves.

It is desired that semiconductor layer4has a thickness of less than or equal to 10 μm. As the thickness of semiconductor layer4decreases, the deactivation of photo carrier decreases.

A material of ferroelectric layer5may be appropriately determined as long as polarization occurs when an electromagnetic wave having a detection wavelength enters ferroelectric layer5made of the material. The material of ferroelectric layer5contains, for example, at least any one of barium titanate (BaTiO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), strontium titanate (SrTiO3), lead zirconate titanate (PZT), strontium bismuth tantalate (SBT), bismuth ferrite (BFO), zinc oxide (ZnO), hufnium oxide (HfO2) and polyvinylidene fluoride feiroelectric substances that are organic polymers ((PVDF, P(VDF-TrFE), P(VDF-TrFE-CTFE) and so on). Also, ferroelectric layer5may be configured by laminating or mixing a plurality of different ferroelectric materials.

The material of ferroelectric layer5is not limited to the above materials as long as the material is a pyroelectric substance exerting the pyroelectric effect. Specifically, it is only required that the material of ferroelectric layer5is a ferroelectric substance in which polarization changes with the change in thermal energy inside ferroelectric layer5. In the pyroelectric effect, an electromagnetic wave simply acts as a heat source. Therefore, the pyroelectric effect does not basically have wavelength dependency. Therefore, ferroelectric layer5does not basically have wavelength dependency. Therefore, ferroelectric layer5has sensitivity for a broad band of electromagnetic waves.

The material of ferroelectric layer5may be a material having spontaneous polarization. When the material of ferroelectric layer5is a material having spontaneous polarization, the spontaneous polarization reduces as the temperature of ferroelectric layer5elevates by application of electromagnetic wave. Therefore, the photo carrier injected from ferroelectric layer5to two-dimensional material layer1and semiconductor layer4reduces.

Preferably, ferroelectric layer5is so configured that the change speed of dielectric polarization inside ferroelectric layer5is as fast as possible. Specifically, it is desired to make the thickness (film thickness) of ferroelectric layer5be as small as possible as far as voltage can be applied between two-dimensional material layer1and semiconductor layer4.

It is desired that the thickness of ferroelectric layer5is such a thickness that the largest possible voltage is applied between two-dimensional material layer1and semiconductor layer4when an electromagnetic wave is applied to two-dimensional material layer1. While the polarization direction of ferroelectric layer5is not particularly limited, the polarization direction is desirably such a direction that voltage is applied between two-dimensional material layer1and semiconductor layer4.

On ferroelectric layer5, an unillustrated protective film may be provided. The unillustrated protective film may be provided in such a manner to cover two-dimensional material layer1, first electrode portion2a, and semiconductor layer4. A material of the protective film is, for example, an insulating substance such as an oxide or a nitride or the like. Examples of the material of the protective film include silicon oxide (SiO2), silicon nitride (SiN), hafnium oxide (HfO2), aluminum oxide (Al2O3), boron nitride (BN) and the like.

Electromagnetic wave detector100may further include an unillustrated Mot insulator. The unillustrated Mot insulator is so configured that physical properties such as temperature varies due to occurrence of photo-induced phase transition by application of light. The unillustrated Mot insulator is in contact with ferroelectric layer5.

<Method for Producing Electromagnetic Wave Detector100>

Next, referring toFIG.1, a method for producing electromagnetic wave detector100according to Embodiment 1 is described.

A method for producing electromagnetic wave detector100includes a preparatory step, a second electrode portion forming step, a ferroelectric layer forming step, an insulating film forming step, a first electrode portion forming step, an opening forming step, and a two-dimensional material layer forming step.

First, the preparatory step is performed. In the preparatory step, as shown inFIG.1, a flat semiconductor substrate containing silicon (Si) or the like is prepared as semiconductor layer4. The material of the semiconductor substrate is a material having sensitivity to a predetermined detection wavelength.

Subsequently, the second electrode portion forming step is performed. In the second electrode portion forming step, a protective film is formed on first surface4aof semiconductor layer4. The protective film is, for example, a resist. In the state that first surface4aof semiconductor layer4is protected by the protective film, second electrode portion2bis deposited on second surface4bof semiconductor layer4. Before deposition of second electrode portion2b, an unillustrated close adherence layer may be formed in a region of second surface4bof semiconductor layer4where second electrode portion2bis to be deposited. The second electrode portion forming step may be performed after any step from the ferroelectric layer forming step to the two-dimensional material layer1forming step as long as first surface4aof semiconductor layer4is protected by the protective film.

Subsequently, the ferroelectric layer forming step is performed. In the ferroelectric layer forming step, ferroelectric layer5is formed on semiconductor layer4. A method for forming the ferroelectric layer may be appropriately determined. For example, when ferroelectric layer5is formed of a polymer material, ferroelectric layer5is formed by forming a polymer film by a spin coating method or the like, and then processing the polymer film by a photolithographic method. When the material of ferroelectric layer5is a material other than a polymer material, after formation of ferroelectric layer5by sputtering, vapor deposition or a metal organic decomposition method (MOD coating method, MOD: Metal Organic Composition), an ALD (Atomic Layer Deposition) method or the like, ferroelectric layer5is patterned by a photolithography method. Also, a method called lift-off may be used. In the method called lift-off, after depositing ferroelectric layer5by using a resist mask is used as a mask, the resist mask is removed.

Subsequently, the insulating film forming step is performed. In the insulating film forming step, insulating film3is formed on the surface of semiconductor layer4and ferroelectric layer5. For example, when the material of semiconductor layer4is silicon (Si), insulating film3may be heat-oxidized silicon oxide (SiO2). Also, the method of depositing insulating film3may be a CVD (Chemical Vapor Deposition) method or a sputtering method.

Subsequently, the first electrode portion forming step is performed. In the first electrode portion forming step, first electrode portion2ais formed on insulating film3. Before formation of first electrode portion2a, a close adherence layer may be formed in a region of insulating film3where first electrode portion2ais to be formed.

As a method for forming first electrode portion2a, for example, the following process is used. First, a resist mask is formed on insulating film3by photochemical engraving or electron beam (EB) lithography. In a region of the resist mask where first electrode portion2ais to be formed, an open part is formed. Thereafter, a film of metal or the like that is to be first electrode portion2ais formed on the resist mask. For formation of the film, an evaporation method or a sputtering method or the like is used. At this time, the film is formed to extend from inside the open region of the resist mask to the top surface of the resist mask. Thereafter, the resist mask is removed together with a part of the film. The other part of the film having been arranged in the open region of the resist mask remains on insulating film3to become first electrode portion2a. The above-described method is generally called a lift-off method.

As a method for forming first electrode portion2a, other method may be used. For example, on insulating film3, a film such as a metal film that is to be first electrode portion2ais previously deposited. Thereafter, a resist mask is formed on the film by the photolithography method. The resist mask is formed to cover the region where first electrode portion2ais to be formed, but is not formed in the region other than the region where first electrode portion2ais to be formed. Thereafter, the film is partially removed by the wet etching or dry etching with the resist mask being a mask. As a result, a part of the film remains under the resist mask. The part of the film becomes first electrode portion2a. Thereafter, the resist mask is removed. First electrode portion2amay be formed in this manner.

Subsequently, the opening forming step is performed. In the opening forming step, insulating film3is provided with opening OP. Specifically, an unillustrated resist mask is formed on insulating film3by photochemical engraving or electron beam lithography. An open part is formed in a region of the resist mask where opening OP is to be formed in insulating film3. Thereafter, insulating film3is etched with the resist mask being an etching mask. The etching technique is appropriately selected from either of the wet etching and the dry etching. After the etching, the resist mask is removed. The opening forming step may be performed previous to the first electrode portion forming step.

Subsequently, the two-dimensional material layer forming step is performed. In the two-dimensional material layer forming step, two-dimensional material layer1is formed so that first electrode portion2a, insulating film3, and semiconductor layer4exposed inside opening OP are coved with two-dimensional material layer1. The method for forming two-dimensional material layer1is not particularly limited. Two-dimensional material layer1may be formed, for example, by epitaxial growth, or may be formed by screen printing. Also, two-dimensional material layer1may be formed by transferring and bonding a two-dimensional material film that has been deposited in advance by a CVD method. Two-dimensional material layer1may be formed by transferring and bonding a two-dimensional material film that has been peeled off by mechanical peeling or the like.

After forming two-dimensional material layer1, a resist mask is formed on two-dimensional material layer1by photochemical engraving or the like. The resist mask is formed such that it covers the region where two-dimensional material layer1is to be formed, while exposing the remaining region. Thereafter, two-dimensional material layer1is etched with the resist mask being an etching mask. The etching technique is, for example, dry etching by oxygen plasma. Thereafter, the resist mask is removed. As a result, two-dimensional material layer1shown inFIG.1is formed.

Through the above steps, electromagnetic wave detector100is produced.

While two-dimensional material layer1is formed on first electrode portion2ain the above-described production method, first electrode portion2amay be formed to overlap a part of two-dimensional material layer1after forming two-dimensional material layer1on insulating film3. In this case, however, it is necessary to take care not to injure two-dimensional material layer1by the formation process of first electrode portion2aat the time of forming first electrode portion2a. For example, since first electrode portion2ais formed in the state that other region than the region where first electrode portion2ais to be overlapped in two-dimensional material layer1is preliminarily covered with a protective film or the like, first electrode portion2ais prevented from being injured in the formation process.

<Principle of Operation of Electromagnetic Wave Detector100>

Next, with reference toFIG.1, the principle of operation of electromagnetic wave detector100according to Embodiment 1 is described.

As shown inFIG.1, first, voltmeter VM or ammeter IM (seeFIG.5) is electrically connected between first electrode portion2aand second electrode portion2b. First electrode portion2a, two-dimensional material layer1, semiconductor layer4and second electrode portion2bare electrically connected sequentially. Voltage of a current or a current flowing in two-dimensional material layer1is measured by voltmeter VM or ammeter IM (seeFIG.5). Bias voltage need not be applied to two-dimensional material layer1. When bias voltage is not applied to two-dimensional material layer1, the dark current is zero because no voltage is applied. That is, electromagnetic wave detector100performs an OFF operation.

Next, an electromagnetic wave is applied to ferroelectric layer5. By the pyroelectric effect of ferroelectric layer5, dielectric polarization changes inside ferroelectric layer5. As a result, electric charges are injected into semiconductor layer4from ferroelectric layer5. Accordingly, bias voltage is artificially applied to electromagnetic wave detector100. Therefore, the resistance between first electrode portion2aand second electrode portion2bchanges. The phenomenon that change in Fermi level inside two-dimensional material layer1causes change in resistance of electromagnetic wave detector100is called an photobiasing effect. Change in resistance between first electrode portion2aand second electrode portion2bresults in change in voltage and current between first electrode portion2aand second electrode portion2b. By detection of either of change in voltage and change in current, it is possible to detect the electromagnetic wave applied to electromagnetic wave detector100.

Voltage may further be applied between first electrode portion2aand second electrode portion2b. Preferably, the voltage is set to be forward bias for the Schottky junction between two-dimensional material layer1and semiconductor layer4. By application of the voltage, a current flows in two-dimensional material layer1arranged between first electrode portion2aand second electrode portion2b. Since first electrode portion2ato second electrode portion2bbecome a path in which a current flows, two-dimensional material layer1also becomes a path in which a current flows.

For example, when a semiconductor that forms semiconductor layer4is made of silicon (Si) which is a p-type material, and two-dimensional material layer1is made of graphene which is an n-type material, two-dimensional material layer1and semiconductor layer4are joined by Schottky junction. Thus, by adjusting the voltage so that forward bias is applied to the Schottky junction, it is possible to amplify a variation in current even when the dielectric polarization of ferroelectric layer5is minute.

Further, by application of the electromagnetic wave to ferroelectric layer5, the dielectric polarization of ferroelectric layer5changes by pyroelectric effect, and thus the Fermi level of two-dimensional material layer1or semiconductor layer4modulates. Accordingly, the energy barrier between two-dimensional material layer1and semiconductor layer4deteriorates. Thus, a current flows in semiconductor layer4only when an electromagnetic wave is applied to electromagnetic wave detector100, so that it is possible to detect a current only when an electromagnetic wave is applied to electromagnetic wave detector100.

The configuration of electromagnetic wave detector100is not limited to the aforementioned configuration of detecting change in current. For example, change in voltage between first electrode portion2aand second electrode portion when an electromagnetic wave is applied to electromagnetic wave detector100in the condition that a constant current flows between first electrode portion2aand second electrode portion2bmay be detected. The change in voltage between first electrode portion2aand second electrode portion2bwhen an electromagnetic wave is applied to electromagnetic wave detector100is change in voltage in two-dimensional material layer1.

Also, the above-described electromagnetic wave detector100may be arranged as a first electromagnetic wave detector, and a second electromagnetic wave detector having the same configuration as the first electromagnetic wave detector may further be arranged. The first electromagnetic wave detector is arranged in a space where an electromagnetic wave is applied. The second electromagnetic wave detector is arranged in a space shielded from an electromagnetic wave. The detection may be performed by detecting difference between the current of the first electromagnetic wave detector and the current of the second electromagnetic wave detector. The detection may be performed by detecting difference between the voltage of the first electromagnetic wave detector and the voltage of the second electromagnetic wave detector.

<Operation of Electromagnetic Wave Detector100>

Next, with reference toFIG.1, a specific operation of electromagnetic wave detector100according to Embodiment 1 is described. Description is made for the case where p-type silicon (Si) is used as semiconductor layer4, graphene is used as two-dimensional material layer1and lithium niobate (LiNbO3) is used as ferroelectric layer5.

Voltmeter VM is connected to the Schottky junction between two-dimensional material layer1and semiconductor layer4. The detection wavelength of electromagnetic wave detector100is determined according to the absorption wavelength of lithium niobate (LiNbO3).

Incidence of an electromagnetic wave having a detection wavelength into ferroelectric layer5causes change in dielectric polarization in ferroelectric layer5by the pyroelectric effect. By the change in polarization in ferroelectric layer5, change in voltage occurs inside electromagnetic wave detector100. This is a phenomenon due to the above-described photobiasing effect. Since the mobility of photo carrier in graphene that constitutes two-dimensional material layer1is large, a large displacement current is obtained for slight change in voltage. Therefore, the Fermi level of two-dimensional material layer1largely changes by the pyroelectric effect of ferroelectric layer5. As a result, the energy barrier between two-dimensional material layer1and semiconductor layer4deteriorates. Therefore, large voltage change or current change occurs between first electrode portion2aand second electrode portion2b. Thus, by the pyroelectric effect of ferroelectric layer5, voltage change or current change in electromagnetic wave detector100occurs.

Further, when the change speed of the dielectric polarization of ferroelectric layer5is set to be as short as possible, the time from incidence of the electromagnetic wave into electromagnetic wave detector100to occurrence of change in resistance in two-dimensional material layer1decreases. As a result, delay of amplification of photo carrier by the photobiasing effect is suppressed, and response speed of electromagnetic wave detector100increases.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.1, ferroelectric layer5is electrically connected to at least any one of first electrode portion2a, second electrode portion2band semiconductor layer4. By the pyroelectric effect of ferroelectric layer5, voltage change or current change in electromagnetic wave detector100occurs. The pyroelectric effect of ferroelectric layer5does not depend on the wavelength of the electromagnetic wave. Therefore, the sensitivity of electromagnetic wave detector100does not depend on the quantum efficiency of semiconductor layer4. Therefore, even for a wavelength for which the quantum efficiency of semiconductor layer4decreases, decrease in sensitivity of electromagnetic wave detector100is suppressed. Therefore, the sensitivity of electromagnetic wave detector100improves. Specifically, it is possible to realize high sensitivity that exceeds 100% by quantum efficiency.

More specifically, a variation in current in two-dimensional material layer1caused by polarization in ferroelectric layer5due to pyroelectric effect is larger than a variation in current in a normal semiconductor. Especially, in two-dimensional material layer1, large current change occurs for slight voltage change as compared with a normal semiconductor. For example, when monolayer graphene is used as two-dimensional material layer1, the thickness of two-dimensional material layer1is very thin because it corresponds to a single atomic layer. The mobility of electron in monolayer graphene is large. In this case, the variation in two-dimensional material layer1, calculated from the mobility of electron, thickness and the like in two-dimensional material layer1, is about several hundred times to several thousand times the variation of current in a normal semiconductor. The effect of changing the energy barrier between two-dimensional material layer1and semiconductor layer4due to large change in Fermi level of two-dimensional material layer1by artificially applying bias voltage to electromagnetic wave detector100by the pyroelectric effect of ferroelectric layer5is called an photobiasing effect.

The extraction efficiency of detection current in two-dimensional material layer1greatly improves by the photobiasing effect. The photobiasing effect does not directly enhance the quantum efficiency of a photoelectric conversion material as is a normal semiconductor, but increases the variation in current by incidence of an electromagnetic wave. Therefore, the quantum efficiency of electromagnetic wave detector100calculated from a differential current by incidence of an electromagnetic wave can exceed 100%. Therefore, the detection sensitivity of electromagnetic wave by electromagnetic wave detector100according to the present embodiment is higher, in comparison with a semiconductor electromagnetic wave detector or a graphene electromagnetic wave detector in which photobiasing effect is not applied.

As shown inFIG.1, in electromagnetic wave detector100, an electric field generated from ferroelectric layer5is shielded with respect to two-dimensional material layer1. More specifically, since a part of ferroelectric layer5facing with two-dimensional material layer1, and two-dimensional material layer1sandwich at least any one of first electrode portion2a, second electrode portion2band semiconductor layer4, the electric field generated from ferroelectric layer5is shielded with respect to two-dimensional material layer1. That is, exertion of the electric field effect on two-dimensional material layer1is suppressed. If the electric field generated from ferroelectric layer5is not shielded with respect to two-dimensional material layer1, the Fermi level of two-dimensional material layer1will significantly change by the electric field effect of the electric field generated from ferroelectric layer5. Accordingly, there is a possibility that the detection sensitivity of electromagnetic wave detector100deteriorates due to change in characteristics of electromagnetic wave detector100. In the present embodiment, since the electric field generated from ferroelectric layer5is shielded with respect to two-dimensional material layer1, it is possible to suppress deterioration in detection sensitivity of electromagnetic wave detector100.

As shown inFIG.1, two-dimensional material layer1is electrically connected to semiconductor layer4in opening OP. Two-dimensional material layer1is joined with semiconductor layer4by Schottky junction in opening OP. Therefore, when reverse bias is applied to two-dimensional material layer1, a current does not flow in two-dimensional material layer1. That is, it is possible to prevent a dark current from flowing in two-dimensional material layer1. Therefore, electromagnetic wave detector100can perform an OFF operation. Also, when forward bias is applied to two-dimensional material layer1, large current change is obtained with a small voltage change. Therefore, the sensitivity of electromagnetic wave detector100improves. As a result, it is possible to realize both improvement in sensitivity of electromagnetic wave detector100and OFF operation of electromagnetic wave detector100.

As shown inFIG.1, in insulating film3, opening OP is formed. Accordingly, electromagnetic wave detector100is capable of simultaneously detecting an electromagnetic wave having entered semiconductor layer4through opening OP. By incidence of electromagnetic wave into semiconductor layer4, a photo carrier is generated in semiconductor layer4. The photo carrier is outputted to first electrode portion2athrough two-dimensional material layer1. Two-dimensional material layer1has a part arranged on insulating film3(third part1c). Therefore, the electric field change by the photo carrier generated in semiconductor layer4is applied to two-dimensional material layer1via insulating film3. In comparison with the case where two-dimensional material layer1does not have third part1c, the conductivity of two-dimensional material layer1by the photogating effect is likely to be modulated more largely. Therefore, the sensitivity of electromagnetic wave detector100improves.

Also, the variation in current when an electromagnetic wave is applied to electromagnetic wave detector100includes the variation by photoelectric current generated by photoelectric conversion in two-dimensional material layer1. Therefore, by application of electromagnetic wave to electromagnetic wave detector100, photobiasing effect, photogating effect and photoelectric conversion are generated. Therefore, electromagnetic wave detector100is capable of detecting change in current by the photobiasing effect, photogating effect and photoelectric conversion. Therefore, the sensitivity of electromagnetic wave detector100improves.

As shown inFIG.1, electromagnetic wave detector100is configured to detect an electromagnetic wave by detecting change in at least one of voltage of a current and a current flowing between first electrode portion2aand second electrode portion2bby at least one of voltmeter VM and ammeter IM. Therefore, an electromagnetic wave can be detected by using at least one of voltmeter VM and ammeter IM.

Two-dimensional material layer1contains a material selected from the group consisting of graphene, transition metal dichalcogenide, black phosphorus, silicene, graphene nanoribbon, and borophene. Therefore, it is possible to securely obtain the operation and effect of the present embodiment.

Ferroelectric layer5is arranged such that voltage in a forward bias direction is applied to two-dimensional material layer1and semiconductor layer4. It is possible to obtain large photo current for small voltage change. Therefore, the sensitivity of electromagnetic wave detector100improves.

Silicon (Si) may be used for semiconductor layer4. Therefore, it is possible to form a readout circuit inside semiconductor layer4. This makes it possible to remove the necessity of further forming another circuit outside electromagnetic wave detector100.

Next, referring toFIGS.7to10, a configuration of electromagnetic wave detector100according to Embodiment 2 is described. Embodiment 2 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.FIG.9is a section view in the IX-IX line ofFIG.7.FIG.10is a section view in the X-X line ofFIG.8.

As shown inFIGS.7and8, in electromagnetic wave detector100according to the present embodiment, ferroelectric layer5is arranged so as not to be overlapped with two-dimensional material layer1in plan view. That is, ferroelectric layer5is misaligned from two-dimensional material layer1in plan view. Electromagnetic wave detector100according to the present embodiment is different from electromagnetic wave detector100according to Embodiment 1 in that ferroelectric layer5is arranged so as not to be overlapped with two-dimensional material layer1in plan view. In the present embodiment, the term plan view means viewing electromagnetic wave detector100along the direction from first electrode portion2atoward second electrode portion2b(seeFIGS.9and10).

The electric field generated in ferroelectric layer5is generated along the direction from first electrode portion2atoward second electrode portion2b. That is, the electric field generated in ferroelectric layer5is generate along the direction of plan view.

Ferroelectric layer5may be arranged on first electrode portion2aas shown inFIG.9as long as ferroelectric layer5is arranged so as not to be overlapped with two-dimensional material layer1in plan view. Ferroelectric layer5may be arranged on semiconductor layer4as shown inFIG.10as long as ferroelectric layer5is arranged so as not to be overlapped with two-dimensional material layer1in plan view.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIGS.7and8, ferroelectric layer5is arranged so as not to be overlapped with two-dimensional material layer1in plan view. Therefore, it is possible to prevent the electric field generated in ferroelectric layer5from reaching two-dimensional material layer1. That is, exertion of the electric field effect on two-dimensional material layer1is suppressed. If the electric field generated from ferroelectric layer5is not shielded with respect to two-dimensional material layer1, the Fermi level of two-dimensional material layer1will significantly change by the electric field effect of the electric field generated from ferroelectric layer5. Accordingly, there is a possibility that the detection sensitivity of electromagnetic wave detector100deteriorates due to change in characteristics of electromagnetic wave detector100. In the present embodiment, since ferroelectric layer5is arranged so as not to be overlapped with two-dimensional material layer1in plan view, it is possible to suppress deterioration in detection sensitivity of electromagnetic wave detector100.

Next, referring toFIGS.11and12, a configuration of electromagnetic wave detector100according to Embodiment 3 is described. Embodiment 3 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIGS.11and12, electromagnetic wave detector100according to the present embodiment further includes a third electrode portion2c. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that electromagnetic wave detector100further includes third electrode portion2c. Third electrode portion2cand one of first electrode portion2aand second electrode portion2bsandwich ferroelectric layer5. Third electrode portion2cis in contact with ferroelectric layer5. Electromagnetic wave detector100is configured to detect a detection signal outputted from third electrode portion2c. That is, electromagnetic wave detector100according to the present embodiment is featured by extracting an electric signal from between third electrode portion2cand first electrode portion2aor second electrode portion2b. It is preferred that the polarization direction of ferroelectric layer5is orthogonal to the surface on which the electrode is formed. When electromagnetic wave detector100includes power source PW (seeFIG.6), voltage may be applied to third electrode portion2cby power source PW (seeFIG.6).

InFIG.11, ferroelectric layer5is arranged opposite to semiconductor layer4with respect to first electrode portion2a. Third electrode portion2cis arranged opposite to first electrode portion2awith respect to ferroelectric layer5. Therefore, third electrode portion2cand first electrode portion2asandwich ferroelectric layer5. Therefore, third electrode portion2cand first electrode portion2adirectly sandwich ferroelectric layer5.

InFIG.12, ferroelectric layer5may be arranged opposite to semiconductor layer4with respect to second electrode portion2b. Third electrode portion2cmay be arranged opposite to second electrode portion2bwith respect to ferroelectric layer5. Therefore, third electrode portion2cand second electrode portion2bsandwich ferroelectric layer5. Therefore, third electrode portion2cand second electrode portion2bdirectly sandwich ferroelectric layer5.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIGS.11and12, third electrode portion2cand one of first electrode portion2aand second electrode portion2bsandwich semiconductor layer4. Therefore, electromagnetic wave detector100is featured by extracting an electric signal from between third electrode portion2cand first electrode portion2aor second electrode portion2b. Therefore, it is possible to efficiently extract electric charges generated by polarization change in ferroelectric layer5via third electrode portion2c. Therefore, the sensitivity of electromagnetic wave detector100improves. Also, the detection signal is outputted after passing through ferroelectric layer5and third electrode portion2c. Since ferroelectric layer5has high insulating performance, it is possible to reduce the dark current of electromagnetic wave detector100. Therefore, the sensitivity of electromagnetic wave detector100improves. Also, by applying voltage to the third electrode, it is possible to control the polarization of ferroelectric layer5. As a result, it is possible to increase the polarization change by application of electromagnetic wave. Therefore, the sensitivity of electromagnetic wave detector100improves.

Next, referring toFIG.13, a configuration of electromagnetic wave detector100according to Embodiment 4 is described. Embodiment 4 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.13, electromagnetic wave detector100according to the present embodiment further includes a tunnel insulating layer6. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that electromagnetic wave detector100further includes tunnel insulating layer6. Tunnel insulating layer6is sandwiched between two-dimensional material layer1and semiconductor layer4. Tunnel insulating layer6electrically connects semiconductor layer4and first part1a. Therefore, in the present embodiment, first part1ais connected to semiconductor layer4with tunnel insulating layer6interposed therebetween. Tunnel insulating layer6is arranged inside opening OP.

Tunnel insulating layer6has such a thickness that can form a tunnel current between two-dimensional material layer1and semiconductor layer4when an electromagnetic wave having a detection wavelength enters two-dimensional material layer1and ferroelectric layer5. Tunnel insulating layer6is, for example, an insulating layer having a thickness of greater than or equal to 1 nm and less than or equal to 10 nm. The insulating layer contains at least any one of, for example, a metal oxide such as alumina (aluminum oxide) or hafnium oxide (HfO2), an oxide including a semiconductor such as silicon oxide (SiO) or silicon nitride (Si3N4), and a nitride such as boron nitride (BN).

While the method for preparing tunnel insulating layer6may be appropriately determined, it can be selected, for example, from an ALD (atomic layer deposition) method, a vacuum evaporation method, and a sputtering method. Tunnel insulating layer6may be formed by oxidizing or nitriding the surface of semiconductor layer4. Tunnel insulating layer6may be a natural oxide film formed on the surface of semiconductor layer4.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.13, tunnel insulating layer6is sandwiched between two-dimensional material layer1and semiconductor layer4. Tunnel insulating layer6has such a thickness that can form a tunnel current between two-dimensional material layer1and semiconductor layer4when an electromagnetic wave having a detection wavelength enters two-dimensional material layer1and ferroelectric layer5. Accordingly, a tunnel current is generated by incidence of electromagnetic wave. Therefore, the injection efficiency of photo current injected into two-dimensional material layer1through semiconductor layer4and tunnel insulating layer6improves. As a result, large photo current is injected into two-dimensional material layer1. Therefore, the sensitivity of electromagnetic wave detector100improves. Also, by tunnel insulating layer6, it is possible to suppress leakage current in the junction interface between two-dimensional material layer1and semiconductor layer4. As a result, it is possible reduce the dark current.

Next, referring toFIG.14, a configuration of electromagnetic wave detector100according to Embodiment 5 is described. Embodiment 5 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.14, electromagnetic wave detector100according to the present embodiment further includes a connection conductor CC. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that electromagnetic wave detector100further includes connection conductor CC. Two-dimensional material layer1is electrically connected to semiconductor layer4with connection conductor CC interposed therebetween. Connection conductor CC is arranged inside opening OP.

On the top face of connection conductor CC, two-dimensional material layer1is overlaid. The bottom face of connection conductor CC is electrically connected to first surface4aof semiconductor layer4. Two-dimensional material layer1is electrically connected to the top face of connection conductor CC. The position of the top face of connection conductor CC is the same as the position of the top face of insulating film3. Two-dimensional material layer1extends planarly from the top face of insulating film3onto the top face of connection conductor CC without bending.

The contact resistance between connection conductor CC and two-dimensional material layer1is smaller than the contact resistance between two-dimensional material layer1and semiconductor layer4. The contact resistance between connection conductor CC and semiconductor layer4is smaller than contact resistance between two-dimensional material layer1and semiconductor layer4. The sum of the contact resistance between connection conductor CC and two-dimensional material layer1and the contact resistance between connection conductor CC and semiconductor layer4is smaller than the contact resistance between two-dimensional material layer1and semiconductor layer4.

When an electromagnetic wave enters ferroelectric layer5through connection conductor CC, it is desired that connection conductor CC has high transmittance at the wavelength of electromagnetic wave to be detected by electromagnetic wave (detection wavelength).

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.14, two-dimensional material layer1is electrically connected to semiconductor layer4with connection conductor CC interposed therebetween. The sum of the contact resistance between connection conductor CC and two-dimensional material layer1and the contact resistance between connection conductor CC and semiconductor layer4is smaller than the contact resistance between two-dimensional material layer1and semiconductor layer4. Therefore, it is possible to reduce the contact resistance as compared with the case where two-dimensional material layer1and semiconductor layer4are directly joined. Therefore, it is possible to suppress attenuation of a detection signal of electromagnetic wave. Therefore, the sensitivity of electromagnetic wave detector100improves. Also, since connection conductor CC and semiconductor layer4are joined by Schottky junction, it is possible to suppress the dark current.

It is preferred that the position of the top face of connection conductor CC is the same as the position of the top face of insulating film3. In this case, since two-dimensional material layer1is formed horizontally without being bent, the mobility of photo carrier in two-dimensional material layer1improves. Therefore, it is possible to improve the detection sensitivity of electromagnetic wave detector100.

Next, referring toFIGS.15to17, a configuration of electromagnetic wave detector100according to Embodiment 6 is described. Embodiment 6 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.15, in electromagnetic wave detector100according to the present embodiment, two-dimensional material layer1includes a plurality of first parts1a. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that two-dimensional material layer1includes plurality of first parts1a. Plurality of first parts1aare arranged on semiconductor layer4. Plurality of first parts1aare arranged at an interval from each other.

In the present embodiment, opening OP includes a first opening region OP1, a second opening region OP2, and a third opening region OP3. First opening region OP1, second opening region OP2and third opening region OP3are arranged at an interval from each other. Each of first opening region OP1, second opening region OP2and third opening region OP3penetrates insulating film3. Semiconductor layer4is exposed from insulating film3in each of first opening region OP1, second opening region OP2and third opening region OP3. Two-dimensional material layer1extends from on insulating film3to the inside of each of first opening region OP1, second opening region OP2and third opening region OP3. Two-dimensional material layer1is in contact with semiconductor layer4in first opening region OP1, second opening region OP2and third opening region OP3.

Electromagnetic wave detector100is configured as one pixel. For example, electromagnetic wave detector100is configured as one pixel having a quadrangular plane shape. It is desired that the area of first electrode portion2ais as small as possible at the time of incidence of an electromagnetic wave to ferroelectric layer5. Therefore, first electrode portion2ais arranged at a first corner among four corners of semiconductor layer4. Also, first opening region OP1is arranged at a second corner among four corners of semiconductor layer4. Second opening region OP2is arranged from a third corner to a fourth corner among four corners of semiconductor layer4. As a result, attenuation of electromagnetic wave by first electrode portion2ais suppressed, and a contact area between two-dimensional material layer1and ferroelectric layer5increases. Accordingly, the region that is influenced by polarization change (pyroelectric effect) of ferroelectric layer5enlarges in two-dimensional material layer1, so that the sensitivity of electromagnetic wave detector100improves. It is desired that the area of first electrode portion2aand the area of opening OP are as small as possible.

As shown inFIG.16, a first part1a1of plurality of first parts1ais in contact with semiconductor layer4in first opening region OP1. As shown inFIG.17, a second first part1a2of plurality of first parts1ais in contact with semiconductor layer4in second opening region OP2. A third first part1a3of plurality of first parts1ais in contact with semiconductor layer4in third opening region OP3.

Next, referring toFIGS.18and19, a configuration of electromagnetic wave detector100according to a first modified example of Embodiment 6 is described.FIG.19is a section view in the XIX-XIX line ofFIG.18.

In electromagnetic wave detector100according to the present embodiment, as shown inFIGS.18and19, two-dimensional material layer1includes a plurality of second parts1b. Plurality of second parts1bare arranged on first electrode portion2a. Plurality of second parts1bare arranged at an interval from each other.

Electromagnetic wave detector100according to the present embodiment includes three first electrode portions2a. Two-dimensional material layer1include three second parts1b. Three first electrode portions2aare arranged at a first to a third corners among four corners of semiconductor layer4. Also, plurality of second parts1binclude a first second part1b1, a second second part1b2and a third second part1b3. Each of first second part1b1, second second part1b2and third second part1b3are respectively arranged at the first to the third corners.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.15, plurality of first parts1aare arranged at an interval from each other. Therefore, it is possible to prevent a photo current flowing between first electrode portion2aand semiconductor layer4through plurality of first parts1afrom flowing locally in two-dimensional material layer1as compared with the case where first part1ais single. Also, it is easy to enlarge the contact area between two-dimensional material layer1and semiconductor layer4, as compared with the case where first part1ais single. Therefore, a photo current flowing in two-dimensional material layer1is dispersed. Therefore, the region where a current flows in two-dimensional material layer1caused by the pyroelectric effect of ferroelectric layer5enlarges. Therefore, the detection sensitivity of electromagnetic wave detector100improves.

According to electromagnetic wave detector100according to the first modified example of the present embodiment, as shown inFIG.19, plurality of second parts1bare arranged at an interval from each other. Therefore, it is possible to prevent a photo current flowing between first electrode portion2aand semiconductor layer4through plurality of second parts1bfrom flowing locally in two-dimensional material layer1as compared with the case where second part1bis single. Also, it is easy to enlarge the contact area between two-dimensional material layer1and semiconductor layer4, as compared with the case where second part1bis single. Therefore, a photo current flowing in two-dimensional material layer1is dispersed. Therefore, the region where a current flows in two-dimensional material layer1caused by the pyroelectric effect of ferroelectric layer5enlarges. Therefore, the detection sensitivity of electromagnetic wave detector100improves.

Next, referring toFIGS.20and21, a configuration of electromagnetic wave detector100according to Embodiment 7 is described. Embodiment 7 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.20, first electrode portion2ahas an annular shape in plan view. Semiconductor layer4is exposed from insulating film3on an inner side than first electrode portion2a. Two-dimensional material layer1is electrically connected to semiconductor layer4on an inner side than first electrode portion2a. First electrode portion2ais arranged on the outer circumference of semiconductor layer4.

As shown inFIG.21, opening OP is arranged on an inner side than first electrode portion2a. First electrode portion2ais arranged on insulating film3such that it surrounds opening OP. First part1aof two-dimensional material layer1is electrically connected to semiconductor layer4on an inner side than first electrode portion2a. Opening OP is arranged, for example, in the center of semiconductor layer4.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described. As shown inFIG.20, first electrode portion2ahas an annular shape in plan view. Therefore, it is possible to enlarge the region that is influenced by change in electric field from semiconductor layer4in two-dimensional material layer1while suppressing attenuation of electromagnetic wave by first electrode portion2ato the minimum. Therefore, the sensitivity of electromagnetic wave detector100improves.

Next, referring toFIG.22, a configuration of electromagnetic wave detector100according to Embodiment 8 is described. Embodiment 8 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.22, in electromagnetic wave detector100according to the present embodiment, semiconductor layer4includes a first semiconductor part41and a second semiconductor part42. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that semiconductor layer4includes first semiconductor part41and second semiconductor part42. Semiconductor layer4may further include an unillustrated third semiconductor part. First semiconductor part41is joined with second semiconductor part42. First semiconductor part41is joined with second semiconductor part42by pn junction. Therefore, pn-junction is formed inside semiconductor layer4.

First semiconductor part41is exposed from insulating film3in opening OP. First semiconductor part41is electrically connected to first electrode portion2awith two-dimensional material layer1interposed therebetween. First semiconductor part41is in contact with two-dimensional material layer1and insulating film3. Second semiconductor part42is arranged opposite to two-dimensional material layer1with respect to first semiconductor part41. Second semiconductor part42is electrically connected to second electrode portion2b. InFIG.22, second semiconductor part42is laminated on first semiconductor part41, however, the positional relationship between first semiconductor part41and second semiconductor part42is not limited to this.

Second semiconductor part42has a conductive type that is different from that of first semiconductor part41. First semiconductor part41has a first conductive type. Second semiconductor part42has a second conductive type. The first conductive type is an opposite conductive type to the second conductive type. For example, when the conductive type of first semiconductor part41is n-type, the conductive type of the second semiconductor is p-type. Thus, semiconductor layer4is configured as a diode.

Second semiconductor part42may have an absorption wavelength that is different from that of first semiconductor part41. Semiconductor layer4may be formed as a diode having sensitivity at a wavelength that is different from that of ferroelectric layer5. Also, first semiconductor part41and second semiconductor part42may be configured as a diode having sensitivity at a wavelength that is different from that of ferroelectric layer5.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.22, first semiconductor part41is joined with second semiconductor part42. Therefore, pn-junction is formed inside semiconductor layer4. Thus, semiconductor layer4is configured as a diode. Therefore, it is possible to prevent a dark current from flowing in semiconductor layer4.

When first semiconductor part41and second semiconductor part42are configured as a diode having sensitivity at a wavelength different from that of ferroelectric layer5, the wavelength detectable by electromagnetic wave detector100is a wavelength that is detectable by each of first semiconductor part41, second semiconductor part42and ferroelectric layer5. Therefore, electromagnetic wave detector100is capable of detecting a broad band of wavelengths.

Next, referring toFIG.23, a configuration of electromagnetic wave detector100according to Embodiment 9 is described. Embodiment 9 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.23, in electromagnetic wave detector100according to the present embodiment, ferroelectric layer5includes a first ferroelectric part51and a second ferroelectric part52. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that ferroelectric layer5includes first ferroelectric part51and second ferroelectric part52. Each of first ferroelectric part51and second ferroelectric part52is electrically connected to two-dimensional material layer1and semiconductor layer4.

First ferroelectric part51is arranged in contact with any one of semiconductor layer4, first electrode portion2aand second electrode portion2b. In the present embodiment, first ferroelectric part51is arranged on second electrode portion2b. Second ferroelectric part52is arranged opposite to second electrode portion2bwith respect to first ferroelectric part51, on first ferroelectric part51. Therefore, first ferroelectric part51and second ferroelectric part52are laminated. The arrangement of first ferroelectric part51and second ferroelectric part52is not limited to this.

It is only required that a material of first ferroelectric part51and second ferroelectric part52is a ferroelectric substance in which polarization changes with the change in thermal energy. A wavelength of electromagnetic wave that can be absorbed by first ferroelectric part51is different from a wavelength of electromagnetic wave that can be absorbed by second ferroelectric part52.

Next, referring toFIG.24, a configuration of a first modified example of electromagnetic wave detector100according to Embodiment 9 is described.

As shown inFIG.24, in electromagnetic wave detector100according to the present embodiment, first ferroelectric part51and second ferroelectric part52are placed side by side along the in-plane direction of semiconductor layer4. First ferroelectric part51and second ferroelectric part52are arranged in regions that are different from each other on any one of semiconductor layer4, first electrode portion2aand second electrode portion2b.

A modified example of the present embodiment is different from electromagnetic wave detector100shown inFIG.23in that first ferroelectric part51and second ferroelectric part52are arranged in regions that are different from each other.

First ferroelectric part51is arranged to be overlapped with first part1aof two-dimensional material layer1in plan view. Second ferroelectric part52is arranged to be overlapped with second part1band third part1cof two-dimensional material layer1in plan view.

Polarizability of first ferroelectric part51is different from polarizability of second ferroelectric part52. For example, polarizability of first ferroelectric part51is higher than polarizability of second ferroelectric part52. Polarizabilities of first ferroelectric part51and second ferroelectric part52are designed so that the Fermi level of each of first part1a, second part1band third part1cof two-dimensional material layer1is optimum.

Next, referring toFIG.25, a configuration of a second modified example of electromagnetic wave detector100according to Embodiment 9 is described.

As shown inFIG.25, ferroelectric layer5includes first ferroelectric part51, second ferroelectric part52, a third ferroelectric part53, a fourth ferroelectric part54and a fifth ferroelectric part55. Electromagnetic wave detector100includes third electrode portion2cand a fourth electrode portion2d. First ferroelectric part51is sandwiched between first electrode portion2aand third electrode portion2c. Second ferroelectric part52is sandwiched between first electrode portion2aand insulating film3. Third ferroelectric part53is sandwiched between second electrode portion2band semiconductor layer4. Fourth ferroelectric part54is sandwiched between second electrode portion2band fourth electrode portion2d. Fifth ferroelectric part55is arranged on semiconductor layer4in opening OP. Preferably, polarization direction of each of first ferroelectric part51, second ferroelectric part52, third ferroelectric part53, fourth ferroelectric part54and fifth ferroelectric part55is along the direction in which bias voltage is applied to electromagnetic wave detector100.

The arrangement of first ferroelectric part51, second ferroelectric part52, third ferroelectric part53, fourth ferroelectric part54and fifth ferroelectric part55is not limited to the above arrangement.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.23, ferroelectric layer5includes first ferroelectric part51and second ferroelectric part52. Therefore, it is possible to easily increase the volume of ferroelectric layer5as compared with the case where ferroelectric layer5is made up of only one ferroelectric part. Polarization change of ferroelectric layer5increases with the volume of ferroelectric layer5. Therefore, the sensitivity of electromagnetic wave detector100improves. Also, since the ferroelectric parts are arranged at a plurality of sites, attenuation of the detection signal in the current path of electromagnetic wave detector100decreases. Therefore, the sensitivity of electromagnetic wave detector100improves.

A wavelength of electromagnetic wave that can be absorbed by first ferroelectric part51is different from a wavelength of electromagnetic wave that can be absorbed by second ferroelectric part52. Therefore, electromagnetic wave detector100is capable of detecting wavelengths of a broad band, compared with the case where the wavelengths of electromagnetic wave that can be absorbed by first ferroelectric part51and second ferroelectric part52are the same.

According to electromagnetic wave detector100according to a first modified example of the present embodiment, as shown inFIG.24, polarizability of first ferroelectric part51is different from polarizability of second ferroelectric part52. First ferroelectric part51is electrically connected to first part1aof two-dimensional material layer1. Second ferroelectric part52is electrically connected to second part1band third part1cof two-dimensional material layer1. Therefore, Fermi levels of first ferroelectric part51and second ferroelectric part52can be designed so that the Fenni level in each of first part1a, second part1band third part1cof two-dimensional material layer1is optimum. Therefore, the sensitivity of electromagnetic wave detector100improves.

According to electromagnetic wave detector100according to a second modified example of the present embodiment, as shown inFIG.25, ferroelectric layer5includes first ferroelectric part51, second ferroelectric part52, third ferroelectric part53, fourth ferroelectric part54and fifth ferroelectric part55. Therefore, the volume of ferroelectric layer5increases as compared with the case where ferroelectric layer5is made up of only first ferroelectric part51and second ferroelectric part52. Therefore, the polarization change of ferroelectric layer5further increases. Therefore, the sensitivity of electromagnetic wave detector100further improves.

Next, referring toFIG.26, a configuration of electromagnetic wave detector100according to Embodiment 10 is described. Embodiment 10 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.26, in electromagnetic wave detector100according to the present embodiment, two-dimensional material layer1includes a turbostratic structure part1T. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that two-dimensional material layer1includes turbostratic structure part1T. Turbostratic structure part1T is a structure in which a plurality of graphene layers are laminated in the state that respective lattices of the plurality of graphene layers are mismatched. Two-dimensional material layer1may include turbostratic structure part1T as a part of two-dimensional material layer1, or the entire two-dimensional material layer1may be configured by turbostratic structure part1T. The material of two-dimensional material layer1according to the present embodiment is multilayer graphene.

InFIG.26, third part1cof two-dimensional material layer1is formed of turbostratic structure part1T. In other words, graphene of turbostratic structure is applied only to the part of two-dimensional material layer1arranged on insulating film3. Also, first part1aand second part1bof two-dimensional material layer1need not include turbostratic structure part1T. In other words, the part of two-dimensional material layer1arranged on first electrode portion2aand on semiconductor layer4need not include turbostratic structure part1T. First part1aand second part1bmay be formed of, for example, monolayer graphene. When first part1aand second part1bare formed of monolayer graphene, and third part1cincludes turbostratic structure part1T, it is possible to prevent contact resistance between two-dimensional material layer1and first electrode portion2a, and contact resistance between two-dimensional material layer1and semiconductor layer4from increasing, and it is possible to suppress carrier scattering by insulating film3for two-dimensional material layer1. Although not illustrated, first part1aand second part1bof two-dimensional material layer1may be turbostratic structure part1T.

A method for preparing turbostratic structure part1T may be appropriately determined. For example, turbostratic structure part1I may be formed by transferring monolayer graphene prepared by the CVD method several times to laminate into multilayer graphene. Also, turbostratic structure part1T may be formed by arranging a carbon source such as ethanol, methane or the like on graphene, and growing the graphene by the CVD method.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.26, two-dimensional material layer1includes turbostratic structure part1T. Therefore, it is possible to improve the mobility of carrier in two-dimensional material layer1. Therefore, it is possible to improve the sensitivity of electromagnetic wave detector100.

More specifically, normal multilayer graphene that does not include turbostratic structure part1T is laminated in the state that respective lattices of plurality of graphenes are matched. This state is called A-B multilayer. Meanwhile, multilayer graphene including turbostratic structure part1T is formed in the following manner. Graphene prepared by the CVD method has polycrystals. Therefore, when graphene is further transferred on the graphene plural times, or when graphene is further laminated by the CVD method with the underlying graphene being as a core, lamination is performed in the state that respective lattices of plurality of graphenes are mismatched. That is, turbostratic structure part1T is formed in graphene. Graphene of the turbostratic structure constituting turbostratic structure part1T is less influenced by the interaction between layers, and has the equivalent properties as monolayer graphene. Further, in two-dimensional material layer1, the mobility deteriorates due to the influence of photo carrier scattering in underlying insulating film3. However, in turbostratic structure part1T, the graphene being in contact with the insulating film3is influenced by photo carrier scattering, but the graphene of the upper layer laminated in the turbostratic structure on the graphene is less likely to be influenced by photo carrier scattering of the underlying insulating film3. Also, in the graphene of the turbostratic structure, since the influence of the interaction between layers is small, the conductivity also improves. Based on the above, the mobility of photo carrier improves in the graphene of the turbostratic structure. As a result, the sensitivity of electromagnetic wave detector100improves.

Next, referring toFIGS.27and28, a configuration of electromagnetic wave detector100according to Embodiment 11 is described. Embodiment 11 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.FIG.27is a section view in the XXVII-XXVII line ofFIG.28.

As shown inFIG.27, electromagnetic wave detector100according to the present embodiment further includes a conductor7. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that electromagnetic wave detector100further includes conductor7. Conductor7is arranged so as to be contact with two-dimensional material layer1. Conductor7is not connected to a power circuit or the like. That is, conductor7is configured as a floating electrode. A material of conductor7may be appropriately determined among materials that conduct electricity. Examples of the material of conductor7include metal materials such as gold (Au), silver (Ag), copper (Cu), aluminum (Al), nickel (Ni), chromium (Cr), and palladium (Pd). The material of conductor7is preferably, a material that generates surface plasmon resonance in conductor7.

A method for forming conductor7may be appropriately determined. The method for forming conductor7may be the same as the production method of first electrode portion2adescribed in Embodiment 1.

In the present embodiment, conductor7includes a plurality of conductive parts70. Plurality of conductive parts70are arranged at an interval from each other. The material of conductive part70is preferably, a material that generates surface plasmon resonance in conductive part70. Each of conductive parts70is configured as a floating electrode.

In the present embodiment, plurality of conductive parts70have a one-dimensional (seeFIG.28) or two-dimensional (seeFIG.29) periodical structure. Among plurality of conductive parts70, neighboring conductive parts70are preferably arranged at such an interval that surface plasmon resonance is generated in each of plurality of conductive parts70.

As shown inFIG.28, plurality of conductive parts70may have a one-dimensional periodical structure. Among plurality of conductive parts70, neighboring conductive parts70are arranged at regular intervals along the first direction.

As shown inFIG.29, plurality of conductive parts70may have a two-dimensional periodical structure. Among plurality of conductive parts70, neighboring conductive parts70are arranged at regular intervals along the first direction and the second direction. The second direction intersects with the first direction. InFIG.29, plurality of conductive parts70are arranged at positions corresponding to lattice points of tetragonal lattice. Plurality of conductive parts70may be arranged, for example, at positions corresponding to lattice points of triangular lattice. Although not illustrated, the arrangement of plurality of conductive parts70is not limited to a periodically symmetric arrangement. Also, the arrangement of plurality of conductive parts70may be an asymmetric arrangement in plan view. InFIGS.28and29, the plane form of plurality of conductive parts70is a quadrangle, but the form of plurality of conductive parts70is not limited to this. The plane form of plurality of conductive parts70may be, for example, a circle, or a polygon such as triangle, or may be an oval shape and the like.

Also, as shown inFIG.30, plurality of conductive parts70may be arranged between two-dimensional material layer1and semiconductor layer4. Although not illustrated, two-dimensional material layer1may include a plurality of recesses or a plurality of protrusions. The plurality of recesses may have a periodical structure or an asymmetrical structure. The plurality of protrusions may have a periodical structure or an asymmetrical structure.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.27, conductor7is arranged so as to be in contact with two-dimensional material layer1. Therefore, the photo carrier generated by application of electromagnetic wave in ferroelectric layer5can migrate through conductor7. The life span of photo carrier in conductor7is longer than the life span of photo carrier in two-dimensional material layer1. Therefore, migration of the photo carrier through conductor7elongates the life span of the photo carrier. Therefore, the sensitivity of electromagnetic wave detector100improves.

As shown inFIG.27, conductor7includes plurality of conductive parts70. Plurality of conductive parts70are arranged at an interval from each other. Further as shown inFIG.28, among plurality of conductive parts70, neighboring conductive parts70are arranged at regular intervals along the first direction. Also, the material of conductive part70is a material that generates surface plasmon resonance in conductive part70. Therefore, electromagnetic wave detector100is capable of detecting only an electromagnetic wave having polarization that generates surface plasmon resonance in conductive part70. That is, polarization dependency arises in plurality of conductive parts70according to the electromagnetic wave applied to electromagnetic wave detector100.

As shown inFIG.29, among plurality of conductive parts70, neighboring conductive parts70are arranged at regular intervals along the first direction and the second direction. Also, the material of conductive part70is a material that generates surface plasmon resonance in conductive part70. Therefore, electromagnetic wave detector100is capable of detecting only an electromagnetic wave having a wavelength that generates surface plasmon resonance in conductive part70with high sensitivity.

As shown inFIG.30, plurality of conductive parts70are arranged between two-dimensional material layer1and semiconductor layer4. Therefore, two-dimensional material layer1covers plurality of conductive parts70. Accordingly, there is no need to form plurality of conductive parts70on two-dimensional material layer1. Therefore, it is possible to prevent two-dimensional material layer1from being injured in formation of plurality of conductive parts70. Therefore, it is possible to prevent mobility of photo carrier from deteriorating in two-dimensional material layer1.

Although not illustrated, the arrangement of plurality of conductive parts70may be an asymmetric arrangement in plan view. In this case, electromagnetic wave detector100is capable of detecting only an electromagnetic wave having polarization that generates surface plasmon resonance in conductive part70.

Although not illustrated, two-dimensional material layer1may include a plurality of recesses or protrusions. Plurality of recesses or protrusions are arranged at such an interval that surface plasmon resonance is generated. Since two-dimensional material layer1has high conductivity, surface plasmon resonance is generated in two-dimensional material layer1. Therefore, likewise the surface plasmon resonance by plurality of conductive parts70as described above, surface plasmon resonance is generated in two-dimensional material layer1by plurality of recesses or protrusions. Therefore, electromagnetic wave detector100is capable of detecting only an electromagnetic wave having polarization or frequency that generates surface plasmon resonance in two-dimensional material layer1.

Next, by referring toFIG.31, a configuration of electromagnetic wave detector100according to Embodiment 12 is described. Unless otherwise described, Embodiment 12 has the same configuration and effect as above Embodiment 1. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.31, electromagnetic wave detector100according to the present embodiment further includes a contact layer8. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that electromagnetic wave detector100further includes contact layer8. Contact layer8is arranged so as to be contact with two-dimensional material layer1. Contact layer8is in contact with each of first part1a, second part1band third part1cof two-dimensional material layer1. Contact layer8is configured to supply two-dimensional material layer1with holes or electrons (photo carrier) by coming into contact with two-dimensional material layer1. That is, contact layer8is configured to dope two-dimensional material layer1with holes or electrons.

Although not illustrated, contact layer8may be formed only on the surface of either first part1aor second part1b. As a result, gradient of charge density is formed inside two-dimensional material layer1. Accordingly, the mobility of photo carrier inside two-dimensional material layer1improves and the sensitivity of electromagnetic wave detector100improves.

Although not illustrated, contact layer8may include a plurality of contact parts. The plurality of contact parts may be laminated on two-dimensional material layer1. The plurality of contact parts may be laminated on two-dimensional material layer1between two-dimensional material layer1and first electrode portion2a. Respective materials of the plurality of contact parts may be the same or different from each other.

The material of contact layer8is, for example, a positive-type photoresist. A positive-type photoresist is a composition containing a photosensitizer having a quinone diazide group, and novolac resin. The material of contact layer8may be for example, a material having a polar group. More specifically, the material of contact layer8may be a material having an electron-attracting group, which is one example of the material having a polar group. The material having an electron-attracting group has the effect of reducing the electron density of two-dimensional material layer1. Examples of the material having an electron-attracting group include materials having a halogen, nitrile, carboxyl group, carbonyl group and the like. Also, the material of contact layer8may be, for example, a material having an electron-donating group, which is one example of the material having a polar group. The material having an electron-donating group has the effect of increasing the electron density of two-dimensional material layer1. Examples of the material having an electron donating group include materials having an alkyl group, alcohol, amino acid, hydroxy group and the like. The material of contact layer8may be an organic substance, metal, a semiconductor, an insulator, a two-dimensional material or a mixture of any of these materials as long as polarization of charges occurs and polarity is generated in the entire molecule.

When the material of contact layer8is an inorganic substance, two-dimensional material layer1is doped to p-type if the work function of contact layer8is larger than the work function of two-dimensional material layer1. When the material of contact layer8is an inorganic substance, two-dimensional material layer1is doped to n-type if the work function of contact layer8is smaller than the work function of two-dimensional material layer1. When the material of contact layer8is an organic substance, the organic substance does not have a definite work function. Therefore, it is desired to determine to which one of n-type and p-type two-dimensional material layer1is to be doped by determining the polar group of the material of contact layer8according to the polarity of the molecule of the organic substance constituting the material of contact layer8.

For example, when a positive-type photoresist is used as contact layer8, the region where a resist is formed by photolithography step in two-dimensional material layer1becomes p-type two-dimensional material layer1region. Accordingly, the treatment of forming a mask contacting on the surface of two-dimensional material layer1is no longer required. As a result, it is possible to suppress injury of two-dimensional material layer1by the process of forming a mask. Also, it is possible to simplify the process.

The material of contact layer8may be a material in which polarity conversion occurs by application of an electromagnetic wave to contact layer8. By occurrence of polarity conversion in contact layer8, electrons or holes generated at the time of polarity conversion are supplied to two-dimensional material layer1. Therefore, the part of two-dimensional material layer1being in contact with contact layer8is doped with electrons or holes. Therefore, after removal of contact layer8, the part of two-dimensional material layer1having been in contact with contact layer8remains in the condition it is doped with electrons or holes. Therefore, when a material in which polarity conversion occurs is used as the material of contact layer8, contact layer8may be removed from on two-dimensional material layer1after occurrence of polarity conversion. The area of the open part of two-dimensional material layer1increases compared with the case where contact layer8is arranged. Therefore, it is possible to improve the detection sensitivity of electromagnetic wave detector100. Polarity conversion is a phenomenon that a polar group chemically converts, and means, for example, the phenomenon such as conversion from an electron-attracting group to an electron-donating group, conversion from an electron-donating group to an electron-attracting group, conversion from a polar group to a non-polar group, or conversion from a non-polar group to a polar group.

By selecting a material in which polarity conversion occurs at a detection wavelength as the material of contact layer8, polarity conversion occurs in contact layer8only when an electromagnetic wave having the detection wavelength is applied. Accordingly, doping to two-dimensional material layer1is conducted only when an electromagnetic wave having a detection wavelength is applied. As a result, it is possible to increase the photo current flowing into two-dimensional material layer1.

Also, the material of contact layer8may be a material in which oxidation-reduction reaction occurs by application of an electromagnetic wave to contact layer8. Accordingly, it is possible to dope two-dimensional material layer1with electrons or holes generated when oxidation-reduction reaction occurs in contact layer8.

It is preferred that the film thickness of contact layer8is small enough to conduct photoelectric conversion when an electromagnetic wave is applied to two-dimensional material layer1. On the other hand, it is preferred that contact layer8is formed to have such a degree of thickness that a photo carrier is doped to two-dimensional material layer1from contact layer8.

Configuration of contact layer8may be appropriately determined as long as a photo carrier such as a molecule or an electron is supplied to two-dimensional material layer1. For example, by dipping two-dimensional material layer1in a solution, and supplying two-dimensional material layer1with a photo carrier in a molecular level, two-dimensional material layer1may be doped with the photo carrier without formation of solid contact layer8on two-dimensional material layer1.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.31, contact layer8is arranged so as to be in contact with two-dimensional material layer1. Contact layer8is configured to supply two-dimensional material layer1with holes or electrons by coming into contact with two-dimensional material layer1. Therefore, the conductive type of two-dimensional material layer1can be an n-type or a p-type. Accordingly, even when a photo carrier is doped from first electrode portion2a, semiconductor layer4and ferroelectric layer5to two-dimensional material layer1, the conductive type of two-dimensional material layer1can be controlled by contact layer8. Therefore, it is possible to improve the performance of electromagnetic wave detector100.

Next, by referring toFIG.32, a configuration of electromagnetic wave detector100according to Embodiment 13 is described. Unless otherwise described, Embodiment 13 has the same configuration and effect as above Embodiment 1. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.32, in electromagnetic wave detector100according to the present embodiment, a gap GAP is provided between insulating film3and two-dimensional material layer1. Two-dimensional material layer1has a surface facing gap GAP. That is, unlike electromagnetic wave detector100according to Embodiment 1, two-dimensional material layer1has a part arranged apart from insulating film3. In opening OP, it is preferred that the height position of the surface of semiconductor layer4is the same as the height position of the surface of first electrode portion2a. Gap GAP is provided between first electrode portion2aand semiconductor layer4. Two-dimensional material layer1extends from on first electrode portion2ato on semiconductor layer4while bridging gap GAP. Other configuration may be employed as long as gap GAP is provided between two-dimensional material layer1and the insulating layer.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.32, gap GAP is provided between insulating film3and two-dimensional material layer1. Therefore, it is possible to remove the influence of scattering of carrier associated with the contact between insulating film3and two-dimensional material layer1. As a result, it is possible to suppress deterioration in mobility of carrier in two-dimensional material layer1. Therefore, it is possible to improve the sensitivity of electromagnetic wave detector100.

Next, by referring toFIG.33, a configuration of electromagnetic wave detector100according to Embodiment 14 is described. Unless otherwise described, Embodiment 14 has the same configuration and effect as above Embodiment 1. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

Electromagnetic wave detector100according to the present embodiment further includes a substrate portion SUB as shown inFIG.33. Electromagnetic wave detector100according to the present embodiment differs from electromagnetic wave detector100according to Embodiment 1 in that electromagnetic wave detector100further includes substrate portion SUB. Two-dimensional material layer1, first electrode portion2a, first electrode portion2aand ferroelectric layer5are arranged on substrate portion SUB. Substrate portion SUB may be appropriately determined. Substrate portion SUB may be configured, for example, by a material that transmits an electromagnetic wave having a detection wavelength. Substrate portion SUB may be, for example, a readout circuit.

While electromagnetic wave detector100includes insulating film3inFIG.33, electromagnetic wave detector100need not include insulating film3. Also, two-dimensional material layer1may further be in contact with unillustrated another substrate portion. When two-dimensional material layer1is in contact with unillustrated another substrate portion, another substrate portion is preferably an insulating substance. When two-dimensional material layer1is not in contact with unillustrated another substrate portion, the material of insulating film3may be appropriately determined, and may be a semiconductor or the like.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.33, two-dimensional material layer1, first electrode portion2a, second electrode portion2band ferroelectric layer5are arranged on substrate portion SUB. Substrate portion SUB is configured, for example, by a material that transmits a detection wavelength. Therefore, an electromagnetic wave can enter ferroelectric layer5through substrate portion SUB from the substrate side. Thus, electromagnetic wave detector100is capable of detecting an electromagnetic wave entered ferroelectric layer5through substrate portion SUB from the substrate portion SUB side. That is, electromagnetic wave detector100is capable of operating by back illumination.

When substrate portion SUB is a readout circuit, electric connection between first electrode portion2aand substrate portion SUB enables electromagnetic wave detector100to read out a detection signal.

Next, by referring toFIG.34, a configuration of an electromagnetic wave detector array200according to Embodiment 15 is described.

As shown inFIG.34, electromagnetic wave detector array200according to the present embodiment has a plurality of electromagnetic wave detectors100according to Embodiments 1 to 14 and later-described Embodiments 16 to 18. The plurality of electromagnetic wave detectors100are arranged side by side along at least one of a first direction DR1and a second direction DR2intersecting first direction DR1. In the present embodiment, plurality of electromagnetic wave detectors100included in electromagnetic wave detector array200are electromagnetic wave detectors100that are the same with each other.

While four electromagnetic wave detectors100are arranged in a 2×2 array in electromagnetic wave detector array200shown inFIG.34, the number of arranged electromagnetic wave detectors100is not limited to this. For example, nine electromagnetic wave detectors100may be arranged in a 3×3 array. In electromagnetic wave detector array200shown inFIG.34, plurality of electromagnetic wave detectors100are arranged two-dimensionally and periodically, however, plurality of electromagnetic wave detectors100may be arranged periodically along one direction. Among plurality of electromagnetic wave detectors100, intervals between neighboring electromagnetic wave detectors100may be equivalent or different from each other.

When respective semiconductor layers4(seeFIG.1) of plurality of electromagnetic wave detectors100are separated from each other, one second electrode portion2b(seeFIG.1) may be used as a common electrode in plurality of electromagnetic wave detectors100. Accordingly, it is possible to reduce the wiring of electromagnetic wave detector array200compared with the case where plurality of second electrode portions2bare independent, and it is possible to enhance the resolution of electromagnetic wave detector array200.

Next, by referring toFIG.35, a configuration of a modified example of electromagnetic wave detector array200according to Embodiment 15 is described.

As shown inFIG.35, plurality of electromagnetic wave detectors included in electromagnetic wave detector array200are electromagnetic wave detectors101to104that are different from each other in kind. Electromagnetic wave detectors101to104that are different from each other are arranged in an array (in matrix). Plurality of electromagnetic wave detectors101to104may respectively have detection wavelengths that are different from each other. Specifically, plurality of electromagnetic wave detectors101to104may respectively have detection wavelength selectivities that are different from each other.

When materials that form respective semiconductor layer4or ferroelectric layer5(seeFIG.1) of plurality of electromagnetic wave detectors101to104have detection wavelengths that are different from each other, for example, a semiconductor material or a ferroelectric material of which detection wavelength is a wavelength of visible light, and a semiconductor material or a ferroelectric material of which detection wavelength is a wavelength of infrared light may be used. For example, when electromagnetic wave detector array200is applied to a vehicle-mounted sensor, electromagnetic wave detector array200can be used as a camera for visible light image during daytime. Further, electromagnetic wave detector army200can be used as an infrared camera during nighttime. With such a configuration, it is no longer necessary to use different cameras according to the detection wavelength of the electromagnetic wave.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector array200according to the present embodiment, as shown inFIG.34, electromagnetic wave detector array200has plurality of electromagnetic wave detectors100according to Embodiments 1 to 14. Therefore, by setting each of plurality of electromagnetic wave detectors100as a detection element, it is possible to make electromagnetic wave detector array200have a function as an image sensor.

According to a modified example of electromagnetic wave detector array200according to the present embodiment, as shown inFIG.35, plurality of electromagnetic wave detectors101to104respectively have detection wavelengths that are different from each other. Therefore, electromagnetic wave detector array200is capable of detecting at least two or more electromagnetic waves having different wavelengths.

In this manner, electromagnetic wave detector array200is capable of discriminating wavelengths of electromagnetic waves in any wave ranges, for example, wave ranges of ultraviolet light, infrared light, terahertz wave, radio wave and the like in the same manner as an image sensor used in visible light range. As a result, it is possible to obtain, for example, a colored image in which difference in wavelength is shown as difference in color.

Also, electromagnetic wave detector array200may be used as a sensor other than an image sensor. Electromagnetic wave detector array200can be used, for example, as a position detecting sensor capable of detecting the position of an object even with a small number of pixels. Also, for example, electromagnetic wave detector array200can be used as an image sensor capable of detecting intensity of an electromagnetic wave at a plurality of wavelengths. Accordingly, it is possible to detect a plurality of electromagnetic waves and obtain a colored image without using a color filter that has been conventionally required in CMOS (complementary MOS) sensor or the like.

Plurality of electromagnetic wave detectors101to104are respectively configured to detect electromagnetic waves having polarizations that are different from each other. Accordingly, it is possible to make electromagnetic wave detector array200have a function as a polarization discriminating image sensor. For example, by arranging plurality of electromagnetic wave detectors100of one unit consisting of four pixels whose polarization angles to be sensed are 0°, 90°, 45°, and 135°, polarization imaging is enabled. The polarization discriminating image sensor enables, for example, discrimination between artifact and natural object, discrimination of material, discrimination of plurality of objects having the same temperature in infrared wave range, discrimination of boundary between a plurality of objects, or improvement in equivalent resolution.

As described above, electromagnetic wave detector array200is capable of detecting electromagnetic waves of a broad wave range. Also, electromagnetic wave detector array200is capable of detecting electromagnetic waves of different wavelengths.

In each embodiment, as the material of at least one of insulating film3, semiconductor layer4and contact layer8, a material that provides two-dimensional material layer1with variation in potential due to change in characteristics by application of an electromagnetic wave may be used. For example, when the material that provides two-dimensional material layer1with variation in potential due to change in characteristics by application of an electromagnetic wave is used as a material of contact layer8, contact layer8need not be in direct contact with two-dimensional material layer1. For example, when contact layer8is capable of providing two-dimensional material layer1with variation in potential, contact layer8may be arranged on the top face or the bottom face of two-dimensional material layer1with insulating film3or the like interposed therebetween.

Examples of the material that provides two-dimensional material layer1with variation in potential due to change in characteristics by application of an electromagnetic wave include quantum dots, ferroelectric materials, liquid crystal materials, fullerenes, rare-earth oxides, semiconductor materials, pn-junction materials, metal-semiconductor junction materials, metal-insulator-semiconductor junction materials, and the like. For example, when a ferroelectric material having a polarization effect (pyroelectric effect) by an electromagnetic wave is used as the ferroelectric material, change in polarization occurs in the ferroelectric material by application of an electromagnetic wave. Thus, two-dimensional material layer1is provided with variation in potential.

Next, by referring toFIG.36, a configuration of electromagnetic wave detector100according to Embodiment 16 is described. Unless otherwise described, Embodiment 16 has the same configuration and effect as above Embodiment 1. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.36, electromagnetic wave detector100according to the present embodiment further includes a thin film dielectric layer91. Thin film dielectric layer91is sandwiched between two-dimensional material layer1and semiconductor layer4. Thin film dielectric layer91electrically connects first part1aof two-dimensional material layer1and semiconductor layer4. Therefore, first part1aof two-dimensional material layer1is electrically connected to semiconductor layer4with thin film dielectric layer91interposed therebetween. Thin film dielectric layer91is arranged inside opening OP. Thin film dielectric layer91may be thinner than insulating film3and ferroelectric layer5.

Thin film dielectric layer91is configured such that a current flows when an electromagnetic wave is applied. Thin film dielectric layer91has such a thickness that can generate a photo current between two-dimensional material layer1and semiconductor layer4when an electromagnetic wave having a detection wavelength is applied to two-dimensional material layer1and ferroelectric layer5. Thin film dielectric layer91is configured such that photo current is generated when an electromagnetic wave having a detection wavelength is applied to two-dimensional material layer1and ferroelectric layer5. Thin film dielectric layer91has a thickness of, for example, greater than or equal to 1 nm and less than or equal to 10 nm. It is desired that thin film dielectric layer91is configured such that polarization is generated in a dark state. It is desired that the material of thin film dielectric layer91is a material having such a polarizability that decreases a dark current by generation of polarization in a dark state.

Specific examples of the material of thin film dielectric layer91may be ferroelectric materials such as barium titanate (BaTiO3), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), strontium titanate (SrTiO3), lead zirconate titanate (PZT), strontium bismuth tantalate (SBT), bismuth ferrite (BFO), zinc oxide (ZnO), hufnium oxide (HfO2) and polyvinylidene fluoride ferroelectric substances that are organic polymers ((PVDF, P(VDF-TrFE), P(VDF-TrFE-CTFE) and so on) and the like. The material of thin film dielectric layer91may be a metal oxide such as alumina (aluminum oxide) or hafnium oxide (HfO2), an oxide including a semiconductor such as silicon oxide (SiO) or silicon nitride (Si3N4), and a nitride such as boron nitride (BN). Also, the material of thin film dielectric layer91may be an organic polymer film such as carbon fluoride (CF) polymer film.

While the method for preparing thin film dielectric layer91may be appropriately determined, it can be selected, for example, from an ALD (Atomic Layer Deposition) method, a vacuum evaporation method, and a sputtering method. Thin film dielectric layer91may be formed by oxidizing or nitriding the surface of semiconductor layer4. Thin film dielectric layer91may be a natural oxide film formed on the surface of semiconductor layer4. Also, thin film dielectric layer91may be formed of a reaction product generated by reactive ion etching using carbon tetrafluoride (CF4) or the like.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.36, thin film dielectric layer91is sandwiched between two-dimensional material layer1and semiconductor layer4. Thin film dielectric layer91is configured such that a current flows when an electromagnetic wave is applied. Accordingly, a photo current is generated in electromagnetic wave detector100by incidence of electromagnetic wave. Therefore, the injection efficiency of photo current injected into two-dimensional material layer1through semiconductor layer4and thin film dielectric layer91improves. As a result, larger photo current is injected into two-dimensional material layer1, as compared with the case without thin film dielectric layer91. Therefore, the sensitivity of electromagnetic wave detector100improves.

Thin film dielectric layer91may be configured such that polarization is generated in a dark state. In this case, it is possible to suppress leakage current in the junction interface between two-dimensional material layer1and semiconductor layer4. As a result, it is possible reduce the dark current.

Next, by referring toFIG.37, a configuration of electromagnetic wave detector100according to Embodiment 17 is described. Embodiment 17 has the same configuration and operation and effect as Embodiment 1 unless otherwise described. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIG.37, electromagnetic wave detector100according to the present embodiment further includes a thermoelectric material layer92. Thermoelectric material layer92is sandwiched between two-dimensional material layer1and semiconductor layer4. Two-dimensional material layer1is electrically connected to semiconductor layer4with thermoelectric material layer92interposed therebetween. Thermoelectric material layer92may be connected to two-dimensional material layer1and semiconductor layer4with an unillustrated electrode interposed therebetween. Thermoelectric material layer92is arranged inside opening OP. Thermoelectric material layer92may have the same thickness as insulating film3.

On the top face of thermoelectric material layer92, two-dimensional material layer1is overlaid. It is desired that the height position of the top face of thermoelectric material layer92is the same as the height position of the top face of insulating film3. The bottom face of thermoelectric material layer92is electrically connected to first surface4aof semiconductor layer4.

Thermoelectric material layer92is configured such that a current flows when an electromagnetic wave is applied. Thermoelectric material layer92is configured such that voltage (thermal electromotive force) is generated when the temperature of thermoelectric material layer92varies. Thermoelectric material layer92is configured such that voltage is generated when the temperature of thermoelectric material layer92varies by application of electromagnetic wave. Thermoelectric material layer92is configured to generate the Seebeck effect. The Seebeck effect is the effect of generating electromotive force by temperature difference generated between both ends of two different kinds of metal or semiconductor that are mutually joined. Thermoelectric material layer92is configured to extract the thermal electromotive force generated by the temperature difference from two-dimensional material layer1and semiconductor layer4.

Although not illustrated, for example, thermoelectric material layer92includes a p-type thermoelectric layer and an n-type thermoelectric layer. The p-type thermoelectric layer is, for example, a p-type bismuth telluride. The n-type thermoelectric layer is, for example, an n-type bismuth telluride. The p-type thermoelectric layer and the n-type thermoelectric layer are laminated. The p-type thermoelectric layer and the n-type thermoelectric layer are laminated along the direction in which two-dimensional material layer1and semiconductor layer4are laminated. By application of an electromagnetic wave toward one of the top face and the bottom face of thermoelectric material layer92, the temperature of one of the top face and the bottom face of thermoelectric material layer92becomes relatively high, and the temperature of the other of the top face and the bottom face becomes relatively low. As a result, thermal voltage is generated from thermoelectric material layer92. Therefore, a photo current when an electromagnetic wave is applied to electromagnetic wave detector100increases. Therefore, the sensitivity of electromagnetic wave detector100improves. Also, in a dark state, a dark current can be reduced by pn-junction barrier.

The material of thermoelectric material layer92may be appropriately determined as long as the material converts thermal energy generated by impartment of temperature difference, into electric energy. Examples of the material of thermoelectric material layer92include, p-type bismuth telluride, n-type bismuth telluride, a bismuth-tellurium-based thermoelectric semiconductor material, a telluride-based thermoelectric semiconductor material, an antimony-tellurium-based thermoelectric semiconductor material, a zinc-antimony-based thermoelectric semiconductor material, a silicon-germanium-based thermoelectric semiconductor material, a bismuth selenide-based thermoelectric semiconductor material, a silicide-based thermoelectric semiconductor material, an oxide-based thermoelectric semiconductor material, and a Heusler material. Examples of the bismuth-tellurium-based thermoelectric semiconductor material include bismuth telluride (Bi2Te3) and the like. Examples of the telluride-based thermoelectric semiconductor material include germanium telluride (GeTe) and lead telluride (PbTe) and the like. Examples of the zinc-antimony-based thermoelectric semiconductor material include zinc antimonides (ZnSb, Zn3Sb2and Zn4Sb3) and the like. Examples of the silicon-germanium-based thermoelectric semiconductor material include silicon germanium (SiGe) and the like. Examples of the bismuth selenide-based thermoelectric semiconductor material include bismuth selenide (III) (Bi2Se3) and the like. Examples of the silicide-based thermoelectric semiconductor material includes iron silicide (β-FeSi2), chromium silicide (CrSi2), manganese silicide (MnSi1.73), magnesium silicide (Mg2Si) and the like. Examples of the Heusler material include FeVAl, FeVAlSi and FeVTiAl and the like. It is desired that the material of thermoelectric material layer92is any one of p-type bismuth telluride, n-type bismuth telluride, a bismuth-tellurium-based thermoelectric semiconductor material and a silicide-based thermoelectric semiconductor material. It is desired that the carrier of p-type bismuth telluride is a hole, the Seebeck coefficient of p-type bismuth telluride is a positive value, and configuration of p-type bismuth telluride is represented by BiXTe3Sb2—X (0<X≤0.6). It is desired that the carrier of n-type bismuth telluride is an electron, the Seebeck coefficient of n-type bismuth telluride is a negative value, and configuration of n-type bismuth telluride is represented by Bi2Te3—YSeY(0<Y≤3). It is desired that the p-type bismuth telluride and n-type bismuth telluride are used as a pair. The p-type bismuth telluride and the n-type bismuth telluride may be used as a plurality of pairs that are connected with each other by serial connection. In this case, it is possible to increase the voltage generated by thermoelectric conversion, so that the sensitivity of electromagnetic wave detector100improves.

A method for depositing thermoelectric material layer92may be appropriately determined. Thermoelectric material layer92may be deposited, for example, by a known method such as an arc plasma evaporation method or a flash evaporation method.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIG.37, thermoelectric material layer92is sandwiched between two-dimensional material layer1and semiconductor layer4. Thermoelectric material layer92is configured such that a current flows when an electromagnetic wave is applied. Therefore, it is possible to improve the sensitivity of electromagnetic wave detector100by thermal electromotive force.

Also, since two or more kinds of thermoelectric materials (for example, p-type bismuth telluride and n-type bismuth telluride) are laminated, it is possible to suppress the dark current by the barrier of pn junction or the like.

The height position of the top face of thermoelectric material layer92may be the same as the height position of the top face of insulating film3. In this case, two-dimensional material layer1can be formed linearly across the top face of thermoelectric material layer92and the top face of insulating film3without being bent. Therefore, two-dimensional material layer1may be formed horizontally without being bent. Therefore, the mobility of the photo carrier in two-dimensional material layer1improves.

Also, by making a lamination structure by combining thin film dielectric layer91shown in Embodiment 16 and thermoelectric material layer92, it is possible to generate a larger voltage.

Next, referring toFIGS.38and39, a configuration of electromagnetic wave detector100according to Embodiment 18 is described. Unless otherwise described, Embodiment 18 has the same configuration and effect as above Embodiment 1. Therefore, the same configuration as that in Embodiment 1 is denoted by the same reference numeral, and description thereof is not repeated.

As shown inFIGS.38and39, electromagnetic wave detector100according to the present embodiment further includes a heat generating material layer93. Heat generating material layer93is arranged so as to be in contact with ferroelectric layer5. The position where heat generating material layer93is in contact with ferroelectric layer5may be appropriately determined. Therefore, heat generating material layer93may be arranged in any of upper, lower, left, and right positions with respect to ferroelectric layer5. It is desired that heat generating material layer93be arranged so as to be in contact with a surface on which an electromagnetic wave is applied (incident surface) of ferroelectric layer5.

Heat generating material layer93is configured to generate heat when an electromagnetic wave is applied to heat generating material layer93. That is, heat generating material layer93is configured to generate heat when an electromagnetic wave is applied to heat generating material layer93. Since heat generating material layer93is in contact with ferroelectric layer5, the heat generated when an electromagnetic wave is applied to heat generating material layer93is transmitted to ferroelectric layer5from heat generating material layer93. Heat generating material layer93is configured to transmit the heat generated when an electromagnetic wave is applied to heat generating material layer93, to ferroelectric layer5. Heat generating material layer93has such a thickness that can generate heat when an electromagnetic wave having a detection wavelength is applied to ferroelectric layer5. It is desired that heat generating material layer93is a material that absorbs an electromagnetic wave having a detection wavelength.

Specific examples of the material of heat generating material layer93include a black body material having a metal surface on which a black body paint is applied, graphite, multilayer graphene, a metal oxide such as alumina (aluminum oxide) or hafnium oxide (HfO2), an oxide including a semiconductor such as silicon oxide (SiO) or silicon nitride (Si3N4), or a nitride such as boron nitride (BN). Also, the material of heat generating material layer93may be a plasmon absorber that utilizes surface plasmon resonance in which a metal pattern is periodically formed. Also, the material of heat generating material layer93may be a dielectric multilayer film, a nonreflective coat in which a nanoporous material is used, or an infrared absorbing material such as gold black.

The material of heat generating material layer93may be a thermoelectric material used in thermoelectric material layer92(seeFIG.37). Heat generating material layer93has a contact surface that comes into contact with ferroelectric layer5. Heat generation of heat generating material layer93is transmitted to ferroelectric layer5via the contact surface. Heat generating material layer93configured by a thermoelectric material is configured to generate the Peltier effect by the current generated in ferroelectric layer5. It is desired that heat generating material layer93configured by a thermoelectric material is configured to elevate the temperature of the contact surface by the Peltier effect.

A method for preparing heat generating material layer93may be appropriately determined, and can be selected from known deposition methods such as, for example, an ALD (Atomic Layer Deposition) method, a vacuum evaporation method, a sputtering method, an arc plasma evaporation method and a flash evaporation method and the like. Also, heat generating material layer93may be formed by oxidizing or nitriding the surface of semiconductor layer4.

The configuration of electromagnetic wave detector100according to the present embodiment may be applied to other embodiments.

Subsequently, operation and effect of the present embodiment is described.

According to electromagnetic wave detector100according to the present embodiment, as shown inFIGS.38and39, heat generating material layer93is arranged to be in contact with ferroelectric layer5. Therefore, heat generating material layer93is capable of transmitting the heat generated by application of electromagnetic wave to ferroelectric layer5. Therefore, polarization voltage of ferroelectric layer5generated by application of electromagnetic wave increases. Accordingly, the photo current of electromagnetic wave detector100increases. Therefore, the sensitivity of electromagnetic wave detector100improves.

It is desired that heat generating material layer93configured by a thermoelectric material is configured to elevate the temperature of the contact surface by the Peltier effect when an electromagnetic wave is applied. Therefore, the polarization change in ferroelectric layer5further increases by application of electromagnetic wave. Therefore, the photo current of electromagnetic wave detector100increases. Therefore, the sensitivity of electromagnetic wave detector100improves.

Also, by using in combination with a structure in which thin film dielectric layer91shown in Embodiment 16 or thermoelectric material layer92shown in Embodiment 17 is inserted between semiconductor layer4and two-dimensional material layer1, it is possible to further improve the sensitivity of electromagnetic wave detector100.

It is to be understood that the embodiments disclosed herein are illustrative, but are not restrictive in every respect. The scope of the present disclosure is indicated by the appended claims rather than by the description described above, and it is intended that all modifications within the equivalent meaning and scope of the claims are included.

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