Silicon optoelectronic device and light emitting apparatus using the same

A silicon optoelectronic device and a light-emitting apparatus using the silicon optoelectronic device are provided. The silicon optoelectronic device includes: a substrate based on an n-type or p-type silicon; a doped region formed on one surface of the substrate and doped to an ultra-shallow depth with a predetermined dopant to be an opposite type from that of the substrate to provide a photoelectrical conversion effect by quantum confinement in a p-n junction between the doped region and the substrate; and first and second electrodes formed on the substrate to be electrically connected to the doped region. The silicon optoelectronic device may further include a control layer formed on one surface of the substrate to act as a mask in forming the doped region and to limit the depth of the doped region to be ultra-shallow. The silicon optoelectronic device has excellent efficiency and can be used as either a light-emitting device or a light-receiving device. Since the optoelectronic device uses silicon as a base material, it can be manufactured at low cost.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to silicon optoelectronic devices, and more particularly, to a low-cost, high-efficiency silicon optoelectronic device and a light emitting apparatus using the same.

2. Description of the Related Art

Silicon semiconductor substrates can be used to highly integrate logic devices, operator devices, and drive devices therein with high reliability. Because silicon is cheap, highly integrated circuits can be formed on a silicon substrate at lower cost, compared using a compound semiconductor. For this reason, silicon has been used as a base material for most integrated circuits.

Based on the advantage of silicon, steady efforts have been made to manufacture a silicon based light emitting device so as to implement a low-cost optoelectronic device that can be manufactured by the general process used to form integrated circuits. It has been experimentally confirmed that porous silicon and nano-crystal silicon have the ability to emit light. So, research on this continues.

FIG. 1shows a cross-section of a porous silicon region formed in the surface of a bulk monocrystalline silicon and the energy bandgap between the valence band and conduction band in the porous silicon region.

Porous silicon can be attained by anodic electrochemical dissolution on the surface of bulk monocrystalline silicon (Si) in an electrolyte solution containing, for example, a hydrofluoric (HF) acid solution.

While a bulk silicon is subjected to anodic electrochemical dissolution in an HF solution, a porous silicon region1having a number of pores1ais formed in the surface of the bulk silicon, as shown in FIG.1. In the region where the pores1aare formed, more Si—H bonds exist than in a projection region1b, which is not dissolved by hydrofluoric acid. The energy bandgap between the valence band (Ev) and the conduction band (Ec) appears to be inversed with respect to the shape of the porous silicon region1.

A recession region in the energy bandgap curve, which is surrounded by projection regions and corresponds to the projection region1bsurrounded by the pore region1ain the porous silicon region1, provides a quantum confinement effect so that the energy bandgap in this region is increased over that of the bulk silicon. Also, in this region holes and electrons are trapped, emitting light.

For example, in the porous silicon region1, the projection region1bsurrounded by the pore region1ais formed as a quantum wire of monocrystalline silicon to provide the quantum confinement effect, electrons and holes are trapped by the quantum wire and coupled to emit light. The wavelengths of emitted light range from a near infrared wavelength to a blue wavelength according to the dimension (width and length) of the quantum wire. Here, the period of the porous region1ais, for example, about 5 nm, and the porous silicon region1has a maximum thickness of, for example, 3 nm, as shown in FIG.1.

Therefore, after manufacturing a porous silicon based light-emitting device, as a predetermined voltage is applied to the light-emitting device where the porous silicon region1is formed, a desired wavelength of light can be emitted depending on the porosity of the porous silicon region1.

However, such a porous silicon based light-emitting device as described above is not highly reliable yet as a light-emitting device and has an external quantum efficiency (EQE) as low as 0.1%.

FIG. 2is a sectional view of an example of a nano-crystal silicon-based light-emitting device. Referring toFIG. 2, the nano-crystal silicon-based light-emitting device has a layered structure including a p-type monocystalline silicon substrate2, an amorphous silicon layer3formed on the silicon substrate2, an insulating layer5formed on the amorphous silicon layer3, and lower and upper electrodes6and7formed on the bottom of the silicon substrate2and the top of the insulating layer5, respectively. A nano-crystal silicon4is formed as a quantum dot in the amorphous silicon layer3.

The nano-crystal silicon4is formed in a quantum dot form as the amorphous silicon layer3is rapidly heated to 700° C. in an oxygen atmosphere for recrystallization. Here, the amorphous silicon layer3has a thickness of 3 nm, and the nano-crystal silicon4has a size of about 2-3 nm.

In the light-emitting device using the nano-crystal silicon4described above, as a reverse bias voltage is applied across the upper and lower electrodes7and6, an intensive electric field is generated at the ends of the amorphous silicon layer3between the silicon substrate2and the nano-crystal silicon4so that electrons and holes excited to a high-energy level are generated. The electrons and holes are tunneled into the nano-crystal silicon4and couple to each other therein to emit light. In the nano-crystal silicon-based light-emitting device, the wavelength of light generated therefrom becomes shorter as the size of the nano-crystal silicon quantum dot decreases.

In the light-emitting device using the nano-crystal silicon4described above, it is difficult to control the size and uniformity of the nano-crystal silicon quantum dot, and efficiency is very low.

SUMMARY OF THE INVENTION

To solve the above-described problems, it is an object of the present invention to provide a new silicon optoelectronic device available as a light-emitting device or a light-receiving device, which can be manufactured at low cost with higher efficiency than porous silicon-based and nano-crystal silicon-based light-emitting devices, and to provide a light-emitting apparatus using the silicon optoelectronic device.

To achieve the object of the present invention, there is provided a silicon optoelectronic device comprising: a substrate based on an n-type or p-type silicon; a doped region formed on one surface of the substrate and doped to an ultra-shallow depth with a predetermined dopant to be an opposite type from that of the substrate to provide a photoelectrical conversion effect by quantum confinement in a p-n junction between the doped region and the substrate; and first and second electrodes formed on the substrate to be electrically connected to the doped region.

It is preferable that the silicon optoelectronic device further comprising a control layer formed on one surface of the substrate to act as a mask in forming the doped region and to limit the depth of the doped region to be ultra-shallow. More preferably, the control layer is a silicon oxide layer (SiO2) of an appropriate thickness such that the doped region can be formed to the ultra-shallow depth.

It is preferable that the doped region is formed by non-equilibrium diffusion of the predetermined dopant. More preferably, the predetermined dopant comprises one of boron and phosphorous.

It is preferable that at least one of quantum well, quantum dot, and quantum wire where electron-hole pairs are generated and annihilate is formed in the p-n junction between the doped region and the substrate. As a current is applied across the first and second electrodes, electron-hole pair annihilation occurs in the at least one of quantum well, quantum dot, and quantum wire to emit light, so that the silicon optoelectronic device according to the present invention is available as a light-emitting device. In this case, the silicon optoelectronic device further comprises a plurality of micro-holes in the doped region to enhance the output power of generated light. Preferably, the plurality of micro-holes extend down to a light-emitting region in the p-n junction. Preferably, the plurality of micro-holes have a size of λ/(2n) or integer multiples of λ/(2n), where λ is a particular wavelength of generated light, and n is the refractive index of a medium of the micro-holes.

It is preferable that light incident through the doped region is absorbed in the at least one of quantum well, quantum dot, and quantum wire formed in the p-n junction to generate the electron-hole pairs, so that the silicon optoelectronic device is available as a light-receiving device. In this case, the at least one of quantum well, quantum dot, and quantum wire has a sub-energy bandgap large enough to enable the silicon optoelectronic device to act as a UV detector, preferably, capable of detecting the UV range no longer than 150 nm. Preferably, the first electrode is formed on one surface of the substrate where the doped region is formed, and the second electrode is formed on the other surface of the substrate. Preferably, the first and second electrodes are both formed on one surface of the substrate to be electrically connected to the doped region.

For the silicon optoelectronic device according to the present invention, the substrate is formed of one selected from the group consisting of silicon, silicon carbide, and diamond.

The present invention is also achieved by a light-emitting apparatus comprising at least one silicon optoelectronic device acting as a light-emitting device, the silicon optoelectronic device including: a substrate based on an n-type or p-type silicon; a doped region formed on one surface of the substrate and doped to an ultra-shallow depth with a predetermined dopant to be an opposite type from that of the substrate to provide a photoelectrical conversion effect by quantum confinement in a p-n junction between the doped region and the substrate; and first and second electrodes formed on the substrate to be electrically connected to the doped region.

In the light-emitting apparatus according to the present invention, it is preferable that the silicon optoelectronic device further comprises a control layer formed on one surface of the substrate to act as a mask in forming the doped region and to limit the depth of the doped region to be ultra-shallow. As a current is applied across the first and second electrodes of the silicon optoelectronic device, electron-hole pair annihilation occurs in the p-n junction between the doped region and the substrate to emit light, and the light-emitting apparatus can be used as a display system comprising a plurality of silicon optoelectronic devices arranged in a two-dimensional array. Preferably, the two-dimensional array comprises three silicon optoelectronic devices arranged in each pixel to emit light of different colors.

In the light-emitting apparatus according to the present invention, it is preferable that the three silicon optoelectronic devices emit white light, and the light-emitting apparatus comprises a dichroic color filter on the front surface of the two-dimensional array of the silicon optoelectronic devices.

As a current is applied across the first and second electrodes of the silicon optoelectronic device, electron-hole pair annihilation occurs in the p-n junction between the doped region and the substrate to emit light, and the light-emitting apparatus can be used as an illumination apparatus comprising at least one silicon optoelectronic device.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 3, a silicon optoelectronic device according to a preferred embodiment of the present invention includes a substrate11, a doped region15formed in one surface of the substrate11, and first and second electrodes17and19formed on the substrate11to be electrically connected to the doped region15. Preferably, the silicon optoelectronic device according to the present invention further comprises a control layer13on one surface of the substrate11, which acts as a mask in forming the doped region15and enables formation of the doped region15to a desired ultra-shallow depth. The control layer13can be selectively removed after the formation of the doped region15.

The substrate11is formed of a predetermined semiconductor material including silicon, for example, silicon, silicon carbide, or diamond. The substrate11is doped with an n-type dopant.

The doped region15is formed by non-equilibrium diffusion of a predetermined dopant, for example, boron or phosphorous, into the substrate11through an aperture in the control layer13. The doped region15is doped with an opposite type to the substrate11, for example, a p+-type dopant.

In doping the doped region15, it is preferable that the doped region15is doped to a desired ultra-shallow depth such that at least one of quantum well, quantum dot, and quantum wire is formed between the doped region15and the substrate11, i.e., in a p-n junction14, to provide a quantum confinement effect enabling photoelectrical conversion.

A quantum well is mostly formed in the p-n junction14, but a quantum dot or quantum wire can be formed in the p-n junction14. At least two of the quantum well, quantum dot, and quantum wire may be formed together in the p-n junction14. Hereinafter, the present invention will be described as that wherein a quantum well is formed in the p-n junction14for the purpose of simplicity. Although the present invention is described below as that wherein a quantum well is formed in the p-n junction14, it is appreciated that the quantum well can be regarded as at least one of a quantum well, quantum dot and quantum wire.

FIG. 4Ashows the structure of the p-n junction14as the doped layer15is formed to an ultra-shallow depth by non-equilibrium diffusion.FIG. 4Bshows the energy bands of longitudinal and lateral quantum (QW) wells formed in the p-n junction14ofFIG. 4Aby non-equilibrium diffusion. InFIG. 4B, Ec denotes the conduction band energy level, Ev denotes the valence band energy level, and Ef denotes the Fermi energy level. These energy levels are well known in the semiconductor related field, and thus descriptions thereof will be omitted here.

As shown inFIGS. 4A and 4B, near the p-n junction14, doped layers of different dopant types are alternately formed to provide a quantum well structure. The quantum well and the underlying barrier have a depth of about 2 nm and 3 nm, respectively.

Doping the p-n junction14to form the quantum well to such an ultra-shallow depth can be implemented by controlling the thickness of the control layer13and the diffusion process conditions to be optimal.

By an appropriate diffusion temperature and the deformed potential on the surface of the substrate11, the thickness of the diffusion profile can be adjusted to, for example, 10-20 nm, during the diffusion process. As a result, the quantum well system in such an ultra-shallow diffusion profile is formed. The surface of the substrate11is deformed by the thickness of the initial control layer and pre-surface treatment and the deformation becomes serious while processing.

Preferably, the control layer13is a silicon oxide (SiO2) layer of an appropriate thickness such that the doped layer15can be doped to an ultra-shallow depth. As an example, to form the control layer13, a silicon oxide layer is formed on one surface of the substrate11, and the silicon oxide layer is etched by photolithography to remove an aperture portion for diffusion, thereby resulting in the control layer13having a mask structure.

As is known in the field of diffusion technology, if the thickness of the silicon oxide layer is over an appropriate thickness (thousands of angstroms) or if the diffusion temperature is low, the diffusion is affected by vacancy and results in a deep diffusion profile. In contrast, if the thickness of the silicon oxide layer is less than the appropriate thickness, or if the diffusion temperature is high, the diffusion is affected by self-interstitial of silicon and results in a deep diffusion profile. Therefore, by forming the silicon oxide layer to the appropriate thickness at which self-interstitial of silicon and vacancy are generated in a similar ratio and are coupled to each other so that diffusion of dopants cannot be facilitated, ultra-shallow doping can be achieved. Physical properties related with vacancy and self-interstitial are well known in the field of diffusion technology, and thus detailed descriptions thereof will be omitted.

Alternatively, the substrate11may be doped with a p-type, and the doped layer15may be doped with n+-type.

The first electrode17is formed on one surface of the substrate11where the doped region15is formed, and the second electrode19is formed on the bottom of the substrate11.FIG. 3shows an example of the first electrode17which is formed of a non-transparent metal material, partially in contact with the edge region of the doped layer15. The first electrode17may be formed to cover the entire doped region15using a transparent electrode material such as indium tin oxide (ITO).

In the silicon optoelectronic device according to the present invention, the quantum well where electron-hole pairs are generated and annihilate is formed in the p-n junction14between the doped region15and the substrate11. Therefore, the silicon optoelectronic device according to the present invention can be used as a light-emitting device or a light-receiving device.

For example, as a DC voltage (or current) is applied across the first electrode17and the second electrode19, carriers such as electrons and holes are injected into the quantum well in the p-n junction14and recombine (annihilate) due to the subband energy level in the quantum well. Here, electroluminescence of a variety of wavelengths occurs according to the state where the carriers combine.

When the silicon optoelectronic device according to the present invention is used as a light-emitting device, the intensity of electroluminescence may be amplified if the wavelength of electroluminescence matches the resonance frequency of the micro-cavities resulting from micro-defects in the surface of the substrate11(actually, the surface of the doped layer14). By adjusting the size of micro-cavities in the manufacture of the silicon optoelectronic device, a light-emitting device capable of emitting light ranging from a very short wavelength to a long wavelength, particularly from ultraviolet (UV) to infra red (IR) rays is obtained.

Micro-cavities occur due to the deformed potential. By adjusting the size of the micro-cavities, a particular wavelength of light or a wide wavelength range of light can be emitted.

When the silicon optoelectronic device according to the present invention is used as a light-emitting device, the light-emitting device can emit light of a wide wavelength range with a high external quantum efficiency (EQE) of about 60%.

When the silicon optoelectronic device according to the present invention is used as a light-emitting device, light emitted froth the quantum well of the ultra-shallow p-n junction diverges in every direction. When the silicon optoelectronic device according to the present invention is used as a light-emitting device, a visible range of light directed perpendicular to the surface of the device mostly emits out of the device through micro-defects formed in the surface. Meanwhile, most of the light passing in other directions is absorbed near the internal light-emitting portion of the device, i.e., at the substrate11, and thus it cannot contribute to enhancing light-emitting efficiency.

This is because silicon of the substrate11has a high absorbency to the light of visible range. The absorption coefficient (α) of silicon is in the range of 3000-50000/cm to a visible light and is in the range of 5000-30000/cm to a 400-650 nm light. Supposing that silicon has an absorption coefficient (α) of 2000/cm, the intensity I of the light after passing a distance x in the silicon is given by formula (1) below, where Iodenotes the initial intensity of the light:
I=Ioe(−αx)(1)

According to formula (1) above, the light absorbency after the light travels 20 rim, is far less than 1%. Considering that the doped region15has a thickness of 20-30 nm, the light directed perpendicular to the surface of the device can be emitted above 99.9%. Meanwhile, light travels a relatively longer distance in other directions, so that a considerable amount of light is absorbed by the substrate11.

An embodiment of the silicon optoelectronic device according to the present invention to reduce the absorption of light travelling not perpendicular to the surface of the device and thus enhance light-emitting efficiency is shown in FIG.6.FIG. 7is a partial plan view of the doped region15of FIG.6. InFIG. 6, the same reference numerals as inFIG. 3denote the elements having the same functions as those in FIG.3. Thus, the related descriptions above can be referred to and are not repeated here.

Referring toFIGS. 6 and 7, the embodiment of the silicon optoelectronic device according to the present invention includes a micro-hole25in the surface of the doped region15to externally emit a portion of the light that normally would be absorbed inside the device and thus enhance the output power of the light generated therein. Preferably, the micro-hole25extends down to a light-emitting portion in the p-n junction14.

The micro-hole25may remain empty to be filled with air or a material incapable of absorbing a particular wavelength of light.

To amplify a particular wavelength of light, the size of the micro-hole25is determined to be λ/(2n) or integer multiples of λ/(2n), where λ is the particular wavelength of the light, and n is the effective refractive index of the material or air medium to fill the micro-hole25with respect to the wavelength λ.

In the silicon optoelectronic device having the micro-hole25in the doped region15, a portion of the light diverging in a direction not perpendicular to the surface of the device can be emitted out of the device through the micro-hole25, thereby enhancing light-emitting efficiency. In addition, when the size of the micro-hole25is determined to meet the condition with respect to a particular wavelength of light described above, light of a particular wavelength is amplified.

As described above, the silicon optoelectronic device according to the present invention acts as a light-emitting device, so it can be applied to a light-emitting apparatus such as a display system or illumination system. The light-emitting apparatus includes at least one optoelectronic device according to the present invention.

When the light-emitting apparatus employing the silicon optoelectronic device according to the present invention is for a display system, the silicon optoelectronic device according to the present invention may be arranged in a 2-dimensiononal array, as shown inFIGS. 8 and 9, to construct the light-emitting apparatus.

The optoelectronic device according to the present invention can be manufactured to be much smaller in size using a semiconductor material through the process applied to manufacture a semiconductor device. Thus, it is obvious that the optoelectronic device according to the present invention can be applied to a display system, especially a flat panel solid state display.

FIG. 8shows a light-emitting apparatus capable of implementing RGB full-color display without using a color filter, in which three silicon optoelectronic devices55a,55b,and55caccording to the present invention to emit, for example, the colors R, G, and B, are arranged in each pixel51. It is appreciated that an additional color filter could be installed in the light-emitting apparatus ofFIG. 8to realize much distinct color display.

FIG. 9shows a light-emitting apparatus capable of implementing full-color display with a wavelength-selective color filter80displaced over the 2-dimensonal array70of the silicon optoelectronic devices75which emit white light. It is preferable that three silicon optoelectronic devices75according to the present invention which emit white light are arranged in each pixel71, aligned with R, G, and B elements, respectively, of the color filter80. At this time, the arrangement of the R, G, and B elements of the color filter80may be the same as or similar to the 2-dimensional array50of the silicon optoelectronic devices55a,55b, and55cshown in FIG.8.

The 2-dimensional array50of the silicon optoelectronic devices and/or the arrangement of the R, G, and B elements of the color filter80to realize full-color display can be varied in many different ways.

When the light-emitting apparatus employing the silicon optoelectronic device according to the present invention is an illumination system, at least one silicon optoelectronic device according to the present invention is used to construct the light-emitting apparatus, wherein the number of optoelectronic devices to be used is determined to comply with the use of the illumination system and the illuminance requirement thereto.

The above-description of the light-emitting apparatus employing the silicon optoelectronic device according to the present invention is enough to infer the entire structure of the light-emitting apparatus, and thus a detailed description and illustration thereof will be omitted.

Meanwhile, the silicon optoelectronic device according to the present invention can be used as a light-receiving device as well as a light-emitting device, as described above. In contrast to the silicon optoelectronic device acting as a light-emitting device, in the case where the silicon optoelectronic device acts as a light-receiving device and is irradiated by light, electrons and holes that will obtain energy from the light incident through the doped region15and generate an electric current and then an electrical signal proportional to the amount of the light radiated are generated. As a result, the silicon optoelectronic device can act as a light-receiving device.

When a voltage is vertically or laterally applied to a silicon optoelectronic device according to the present invention, a sub-energy bandgap in the quantum well formed at the p-n junction14can be sufficiently increased, so that the silicon optoelectronic device according to the present invention can be used as a UV detector. In the silicon optoelectronic device shown inFIG. 3having a structure in which the second electrode19is formed on the bottom of the substrate11, a voltage can be vertically applied across the first and second electrodes17and19. Unlike the structure of the silicon optoelectronic device ofFIG. 3, in the silicon optoelectronic device ofFIG. 10, instead of forming the second electrode on the bottom of the substrate11, the first and second electrodes17and19are both formed on the surface of the substrate11where the doped region15has been formed, such that a voltage can be horizontally applied to the device. InFIG. 10, the same reference numerals as inFIG. 3denote the elements having the same or similar function as those inFIG. 3, and descriptions thereof will not be provided here.

UV rays refer to electromagnetic waves having a wavelength ranging from 400 nm to 1 nm (1 keV) within which range “near UV” refers to light of a wavelength over 300 nm and “vacuum UV” refers to light of a wavelength below 200 nm.

The following detectors are commonly used to detect UV rays.

To detect near UV or light of a wavelength longer than 100 nm, detectors for use to detect visible light, such as photodiodes, phototubes, and photomultiplier tubes, are modified to detect UV rays. A radioactive ray detector is used with respect to the wavelength range near X rays.

A silicon photodiode is used as a near-UV detector. The light absorbency of silicon increases as the wavelength of incident light becomes shorter. Accordingly, UV rays are absorbed only at the surface of the detector. Therefore, there is a need to reduce the junction to increase the sensitivity of the UV detector. Generally, silicon detectors are sensitive to light in the range of 200-1100 nm.

In a common detector with a doped region formed using a well known general doping technique, light is absorbed and scatters at the p+(or n+)-doped layer so that it cannot form electron-hole pairs that are vertically extracted through electrodes and contribute to an electrical response. The common detector having the doped region has an indirect bandgap structure to detect only light absorbed by the depletion region underneath the doped region as a current signal, without quantum effect. This indirect bandgap structure reduces the sensitivity of the detector and UV detection efficiency.

Meanwhile, in the silicon optoelectronic device according to the present invention, quantum effect occurs at the ultra-shallow doped region15due to external voltage and localized variations in charge distribution potential. Also, as an external voltage is applied, a sub-energy band is formed in the quantum well, as shown in FIG.11. As a result, the doped region15comes to have an energy bandgap which is wide enough to absorb high-energy UV rays, and the spectrum of the absorption coefficient is changed so that UV rays can be detected with high efficiency. InFIG. 11, reference numeral31denotes the quantum well, and reference numeral33denotes the sub-energy band. Also, “e” denotes an electron, “h” denotes a hole, and “p” denotes a photon. Ev denotes the valance band energy level, and Ec denotes the conduction band energy level.

The silicon optoelectronic device according to the present invention, which has the ultra-shallow doped region15, is highly sensitive to light of a wavelength of 200-1100 nm. Also, the sub-energy bandgap in the quantum well is larger than the bandgap of silicon, so that UV of a very short wavelength no longer than 200 nm can be detected.

A problem with using an UV detector is that UV rays are non-transparent with respect to most materials. Generally, a silicon optoelectronic device is packaged with a transparent window which allows light to enter or exit from the silicon optoelectronic device. Glass (SiO2) for use in forming the transparent window can transmit only UV of a wavelength no shorter than 150 nm.

Therefore, when the silicon optoelectronic device according to the present invention is used as a UV detector, it is preferable that the UV detector has a bared window structure where no glass window is formed to face a light incident side, so that UV of a wavelength no longer than 150 nm can be detected.

As described above, the silicon optoelectronic device according to the present invention has excellent efficiency and can be used as either a light-emitting device or a light-receiving device. Since the optoelectronic device according to the present invention uses silicon as a base material, it can be manufactured at low cost.