Patent Description:
For example, PTL <NUM> discloses a surface-type light emitting element in which an n-type semiconductor multilayered film, a substrate-side contact and injection layer and a p-type semiconductor multilayered film, a cavity including a light emitting layer, and an n-type semiconductor multilayered film are formed on an n-type or semi-insulating GaAs substrate in this order. The n-type semiconductor multilayered film is included in a substrate-side mirror. The n-type semiconductor multilayered film is included in an air-side mirror.

Incidentally, a light emitting device is requested to have higher reliability.

It is desirable to provide a light emitting device that makes it possible to increase the reliability.

A light emitting device according to an embodiment of the present disclosure includes: a substrate; a first contact layer; a buffer layer in which at least any of a carrier concentration, a material composition, and a composition ratio is different from that of the first contact layer; and a semiconductor stacked body. The substrate has a first surface and a second surface that are opposed to each other. The first contact layer is stacked on the first surface of the substrate. The buffer layer is stacked on the first contact layer. The semiconductor stacked body is stacked above the first surface of the substrate with the first contact layer and the buffer layer interposed in between. The semiconductor stacked body has a light emitting region configured to emit laser light.

In the light emitting device according to the embodiment of the present disclosure, the buffer layer in which at least any of the carrier concentration, the material composition, and the composition ratio is different from that of the first contact layer is provided between the first contact layer and the semiconductor stacked body. This forms the semiconductor stacked body having excellent crystal quality.

The scope of the invention is defined by the independent claim followed by dependent claims covering features which are optional.

The following describes an embodiment of the present disclosure in detail with reference to the drawings. The following description is a specific example of the present disclosure, but the present disclosure is not limited to the following modes. In addition, the present disclosure is not limited to the disposition, dimensions, dimensional ratios, or the like of the respective components illustrated in the drawings. It is to be noted that description is given in the following order.

<FIG> schematically illustrates an example of a cross-sectional configuration of a light emitting device (semiconductor laser <NUM>) according to an embodiment of the present disclosure. This semiconductor laser <NUM> is, for example, back-emitting VCSEL (Vertical Cavity Surface Emitting LASER). For example, a plurality of VCSELs is integrated in an array as a plurality of light emitting regions.

The semiconductor laser <NUM> includes, for example, a plurality of semiconductor stacked bodies <NUM> on a first surface (front surface (surface 11S1)) of a substrate <NUM>. Each of the semiconductor stacked bodies <NUM> has, for example, a columnar shape (mesa shape). For example, a first light reflecting layer <NUM>, an active layer <NUM>, and a second light reflecting layer <NUM> are stacked in this order. There is provided a current confining layer <NUM> between the first light reflecting layer <NUM> and the active layer <NUM>. A current injection region 17A is formed in the current confining layer <NUM>. This semiconductor stacked body <NUM> corresponds to a specific example of a "semiconductor stacked body" according to the present disclosure. Between the semiconductor stacked body <NUM> and a substrate <NUM>, a first contact layer <NUM> and a buffer layer <NUM> are stacked in order from the substrate side. The buffer layer <NUM> forms a mesa shape along with the semiconductor stacked body <NUM>. The first contact layer <NUM> extends on the substrate <NUM> as a layer common to the plurality of semiconductor stacked bodies <NUM>. There is provided a first electrode <NUM> on the first contact layer <NUM> as an electrode common to the respective semiconductor stacked bodies <NUM>. A second contact layer <NUM> and a second electrode <NUM> are formed in this order on each of the upper surfaces (surfaces 10S1) of the respective semiconductor stacked bodies <NUM>. Further, the upper surface (surface 12S1) of the first contact layer <NUM> and the upper surface of the second contact layer <NUM> except for the first electrode <NUM> and the second electrode <NUM> and the side surfaces of the second contact layer <NUM>, the semiconductor stacked body <NUM>, and the buffer layer <NUM> are covered with an insulating film <NUM>. The second surface (back surface (surface 11S2)) of the substrate <NUM> is covered with an insulating film <NUM>.

The following describes a configuration, a material, and the like of each section of the semiconductor laser <NUM> in detail.

The substrate <NUM> is a support substrate on which the plurality of semiconductor stacked bodies <NUM> is integrated. The substrate <NUM> includes a semi-insulating substrate including, for example, a GaAs-based semiconductor including, for example, no impurities. In addition, the substrate <NUM> is not necessarily limited to a typical semi-insulating substrate as long as the substrate <NUM> is low in carrier concentration and absorbs less laser light. For example, it is possible to use a substrate having a p-type or n-type carrier concentration of <NUM> × <NUM><NUM> cm-<NUM> or less as the substrate <NUM>.

The first contact layer <NUM> includes, for example, a GaAs-based semiconductor having electrical conductivity. The first contact layer <NUM> is for electrically coupling the first electrode <NUM> and the first light reflecting layer <NUM> of each of the semiconductor stacked bodies <NUM>. The first contact layer <NUM> includes p-type GaAs having, for example, a carrier concentration of <NUM> × <NUM><NUM> cm-<NUM> or more. The first contact layer <NUM> corresponds to a specific example of a "first contact layer" according to the present disclosure. The film thickness of the first contact layer in the stack direction is, for example, <NUM> or more and <NUM> or less.

The buffer layer <NUM> is for recovering the crystal quality of the semiconductor stacked body <NUM> formed above the first contact layer <NUM>. It is preferable that the buffer layer <NUM> have a configuration as follows. In the invention, the buffer layer <NUM> is formed to have a carrier concentration different from that of the first contact layer <NUM>. Specifically, the buffer layer <NUM> includes p-type GaAs having a carrier concentration lower than that of the first contact layer <NUM>. The carrier concentration is less than <NUM> × <NUM><NUM> cm-<NUM>. Preferably, the carrier concentration is <NUM> × <NUM><NUM> cm-<NUM> or less. The buffer layer <NUM> includes a semiconductor having a different material composition and composition ratio from those of the first contact layer <NUM> (e.g., GaAs layer). Examples of materials included in the buffer layer <NUM> include AlAs, AlGaAs, InGaAs, AlGaInAs, GaInP, and AlGaInP. It is possible to form the buffer layer <NUM> as a single layer film or a stacked film including a layer including any of the semiconductor materials described above.

The buffer layer <NUM> includes at least any of those described above. The buffer layer <NUM> hereby alleviates the deterioration of the crystallizability of the first contact layer <NUM> caused by the high-concentration doping and recovers the crystal quality of the semiconductor stacked body <NUM> formed above the first contact layer <NUM>. The film thickness of the buffer layer <NUM> in the stack direction is, for example, <NUM> or more and <NUM> or less.

The first light reflecting layer <NUM> is disposed between the buffer layer <NUM> and the current confining layer <NUM>. The first light reflecting layer <NUM> is opposed to the second light reflecting layer <NUM> with the active layer <NUM> and the current confining layer <NUM> interposed in between. The first light reflecting layer <NUM> resonates the light generated in the active layer <NUM> between the first light reflecting layer <NUM> and the second light reflecting layer <NUM>. The first light reflecting layer <NUM> corresponds to a specific example of a "first light reflecting layer" according to the present disclosure.

The first light reflecting layer <NUM> is a DBR (Distributed Bragg Reflector) layer in which low refractive index layers (not illustrated) and high refractive index layers (not illustrated) are alternately stacked. Each of the low refractive index layers includes, for example, p-type Alx1Ga<NUM>-x1As (<NUM> < x1 ≤ <NUM>) having an optical film thickness of λ×<NUM>/4n and each of the high refractive index layers includes, for example, p-type Alx2Ga<NUM>-x2As (<NUM> ≤ x2 < x1) having an optical film thickness of λ×<NUM>/4n. λ represents the oscillation wavelength of laser light emitted from each of the light emitting regions and n represents the refractive index.

The active layer <NUM> is provided between the first light reflecting layer <NUM> and the second light reflecting layer <NUM>. The active layer <NUM> includes, for example, an aluminum-gallium-arsenide (AlGaAs)-based semiconductor material. In the active layer <NUM>, the holes and electrons injected from the first electrode <NUM> and a second electrode <NUM> undergo radiative recombination to generate stimulated emission light. The region of the active layer <NUM> opposed to the current injection region 17A serves as a light emitting region. For example, undoped Alx3Ga<NUM>-x3As (<NUM> < x3 ≤ <NUM>) is usable for the active layer <NUM>. The active layer <NUM> may have a multi quantum well (MQW: Multi Quantum Well) structure of GaAs and AlGaAs, for example. It is sufficient if a material included in the active layer <NUM> is selected in accordance with the desired wavelength region of laser light. The active layer <NUM> may have a multi quantum well structure of indium gallium arsenide (InGaAs) and AlGaAs, for example, in a case where laser characteristics in a <NUM>-nm band are obtained. The active layer <NUM> corresponds to a specific example of an "active layer" according to the present disclosure.

The second light reflecting layer <NUM> is a DBR layer disposed between the active layer <NUM> and the second contact layer <NUM>. The second light reflecting layer <NUM> is opposed to the first light reflecting layer <NUM> with the active layer <NUM> and the current confining layer <NUM> interposed in between. The second light reflecting layer <NUM> corresponds to a specific example of a "second light reflecting layer" according to the present disclosure.

The second light reflecting layer <NUM> has a stacked structure in which low refractive index layers and high refractive index layers are alternately superimposed. A low refractive index layer is n-type Alx4Ga<NUM>-x4As (<NUM> < x4 ≤ <NUM>) having, for example, an optical film thickness of λ/4n. A high refractive index layer is n-type Alx5Ga<NUM>-x5As (<NUM> ≤ x5 < x4) having, for example, an optical film thickness of λ/4n.

The current confining layer <NUM> is provided between the first light reflecting layer <NUM> and the active layer <NUM>. The current confining layer <NUM> is formed to have an annular shape having a predetermined width from the outer periphery side to the inner side of the semiconductor stacked body <NUM> having, for example, a mesa shape. In other words, the current confining layer <NUM> is provided between the first light reflecting layer <NUM> and the active layer <NUM>. The current confining layer <NUM> has an opening having a predetermined width at the middle portion thereof. This opening serves as the current injection region 17A. The current confining layer <NUM> includes, for example, p-type AlGaAs. Specifically, the current confining layer <NUM> includes Al<NUM>Ga<NUM>As to AlAs. This is oxidized as an aluminum oxide (AlOx) layer to confine currents. Providing the semiconductor laser <NUM> with this current confining layer <NUM> confines currents injected into the active layer <NUM> from the first electrode <NUM> and increases the current injection efficiency.

The second contact layer <NUM> includes, for example, a GaAs-based semiconductor having electrical conductivity. The second contact layer <NUM> includes, for example, n-type GaAs. The second contact layer <NUM> corresponds to a specific example of a "second contact layer" according to the present disclosure.

The first electrode <NUM> is provided on the first contact layer <NUM>. The first electrode <NUM> is formed by using, for example, a multilayered film of titanium (Ti)/platinum (Pt)/gold (Au).

The second electrode <NUM> is provided above the semiconductor stacked body <NUM>. Specifically, the second electrode <NUM> is provided on the second contact layer <NUM>. The second electrode <NUM> is formed by using, for example, a multilayered film of gold-germanium (Au-Ge)/nickel (Ni)/gold (Au).

The insulating film <NUM> is formed, for example, continuously on the upper surfaces of the second contact layers <NUM>, the side surfaces of the second contact layers <NUM>, the semiconductor stacked bodies <NUM>, and the buffer layers <NUM>, and the upper surface (surface 12S1) of the first contact layer <NUM>. The insulating film <NUM> includes, for example, a single layer film such as silicon nitride (SiN) or silicon oxide (SiO<NUM>) or a stacked film. The insulating film <NUM> is provided with the openings <NUM> (see, for example, <FIG>) at predetermined positions on the upper surfaces of the respective second contact layers <NUM> and the first contact layer <NUM>. Each of the openings <NUM> is filled with the first electrode <NUM> or the second electrode <NUM>.

The insulating film <NUM> is formed, for example, on the whole of the back surface (surface <NUM> S2) of the substrate <NUM>. The insulating film <NUM> includes, for example, a single layer film such as silicon nitride (SiN) or silicon oxide (SiO<NUM>) or a stacked film as with the insulating film <NUM>.

The semiconductor laser <NUM> according to the present embodiment is a semiconductor laser having a so-called anode common structure in which the plurality of semiconductor stacked bodies <NUM> and the first electrode <NUM> provided on the substrate <NUM> are electrically coupled to each other by the first contact layer <NUM> including, for example, p-type GaAs.

In a case where predetermined voltages are applied to the first electrode <NUM> and the second electrode <NUM>, voltages are applied from the first electrode <NUM> and the second electrode <NUM> to the semiconductor stacked body <NUM> in the semiconductor laser <NUM>. This injects an electron to the active layer <NUM> from the first electrode <NUM> and injects a hole to the active layer <NUM> from the second electrode <NUM>. The recombination of the electron and the hole generates light. Light is resonated and amplified between the first light reflecting layer <NUM> and the second light reflecting layer <NUM> and laser light L is emitted from the back surface (surface <NUM> S2) of the substrate <NUM>.

Next, a method of manufacturing the semiconductor laser <NUM> is described with reference to <FIG>.

First, as illustrated in <FIG>, the respective compound semiconductor layers included in the first contact layer <NUM>, the buffer layer <NUM>, the first light reflecting layer <NUM>, the active layer <NUM>, the second light reflecting layer <NUM>, and the second contact layer <NUM> are formed in this order on the substrate <NUM>, for example, in an epitaxial crystal growth method such as an organometallic vapor growth (Metal Organic Chemical Vapor Deposition: MOCVD) method. In this case, a methyl-based organic metal compound such as trimethylaluminum (TMAl), trimethylgallium (TMGa), or trimethylindium (TMIn) and an arsine (AsH<NUM>) gas are used as raw materials of the compound semiconductor, disilane (Si<NUM>H<NUM>), for example, is used as a raw material of a donor impurity, and carbon tetrabromide (CBr<NUM>), for example, is used as a raw material of an acceptor impurity.

Subsequently, as illustrated in <FIG>, a resist film (not illustrated) having a predetermined pattern is formed on the second contact layer <NUM> and this resist film is then used as a mask to etch the second contact layer <NUM>, the second light reflecting layer <NUM>, the active layer <NUM>, and the first light reflecting layer <NUM> and form a mesa structure (semiconductor stacked body <NUM>) having a columnar shape. In this case, it is preferable to use, for example, RIE (Reactive Ion Etching) with a Cl-based gas. In the etching of the second contact layer <NUM>, the second light reflecting layer <NUM>, the active layer <NUM>, and the first light reflecting layer <NUM>, the buffer layer <NUM> functions as an etching stop layer. This makes the etching depth constant in the wafer plane. After that, high-temperature treatment is performed in a water vapor atmosphere to oxidize, for example, an AlGaAs layer having a high aluminum (Al) composition and form an oxidation layer (current confining layer <NUM>) for current confinement. The AlGaAs layer has been stacked in advance at the time of epitaxial growth.

Next, as illustrated in <FIG>, the buffer layer <NUM> is removed by etching to expose the first contact layer <NUM>.

Subsequently, as illustrated in <FIG>, the continuous insulating film <NUM> is formed on the first contact layer <NUM> from the upper surface of the second contact layer <NUM> and the insulating film <NUM> is formed on the back surface (surface 11S2) of the substrate <NUM>. After that, the first electrode <NUM> and the second electrode <NUM> are respectively formed on the first contact layer <NUM> and the second contact layer <NUM>. Each of the insulating films <NUM> and <NUM> is formed, for example, in a chemical vapor growth (CVD: Chemical Vapor Deposition) method or an atomic layer deposition (ALD: Atomic Layer Deposition) method. The insulating film <NUM> is formed to cover the whole of the upper surface (surface 12S1) of the first contact layer <NUM> exposed by etching from the upper surface of the second contact layer <NUM>. After that, a resist film (not illustrated) having a predetermined pattern is patterned on the insulating film <NUM> and etching such as RIE is performed to form the opening <NUM> at a predetermined position. After that, the first electrode <NUM> and the second electrodes <NUM> are respectively patterned on the first contact layer <NUM> and the upper surfaces of the second contact layers <NUM> by using a lift-off method in which a resist pattern is, for example, used. This completes the semiconductor laser <NUM> illustrated in <FIG>.

In the semiconductor laser <NUM> according to the present embodiment, the buffer layer <NUM> in which any of the carrier concentration, the material composition, and the composition ratio is different from that of the first contact layer <NUM> is provided between the first contact layer <NUM> and the semiconductor stacked body <NUM>. This forms the semiconductor stacked body <NUM> having excellent crystal quality. The following describes this.

A typical surface emitting laser is provided with a contact layer, for example, in the middle of a DBR layer as in the surface-type light emitting element described above. A voltage is applied to a light emitting layer (active layer) through an electrode provided on this contact layer. The contact layer is therefore formed to have a high carrier concentration in general. In a case where the contact layer having a high carrier concentration is formed at a position close to the active layer in the DBR layer in this way, the contact layer may have increased light absorption and the laser oscillation characteristics may be decreased. Meanwhile, in a case where the contact layer has a smaller film thickness to reduce the light absorption of the contact layer, the margin for processing may disappear and the manufacturing yield may be decreased. In addition, a contact layer doped with a high concentration of impurities tends to have deteriorated crystallizability. The crystallizability of a device structure grown on the contact layer may be thus decreased.

In contrast, in the present embodiment, the buffer layer <NUM> in which any of the carrier concentration, the material composition, and the composition ratio is different from that of the first contact layer <NUM> is provided on the first contact layer <NUM>. The first light reflecting layer <NUM>, the active layer <NUM>, and the second light reflecting layer <NUM> included in the device structure (semiconductor stacked body <NUM>) undergo crystal growth through this buffer layer <NUM>. This makes it possible to alleviate the deterioration of the crystallizability of the first contact layer <NUM> and form the semiconductor stacked body <NUM> whose crystal quality is maintained.

As described above, in the semiconductor laser <NUM> according to the present embodiment, the buffer layer <NUM> in which any of the carrier concentration, the material composition, and the composition ratio is different from that of the first contact layer <NUM> is provided between the first contact layer <NUM> and the semiconductor stacked body <NUM>. This makes it possible to maintain the crystal quality of the semiconductor stacked body <NUM> formed above the first contact layer (e.g., on the buffer layer <NUM>). This makes it possible to increase the reliability.

In addition, in the present embodiment, the buffer layer <NUM> is provided between the first contact layer <NUM> and the semiconductor stacked body <NUM>. This increases the design freedom of the film thickness of the first contact layer. This makes it possible to reduce the light absorption of the first contact layer while suppressing a decreasing process margin. This makes it possible to increase the oscillation characteristics of the laser light L emitted from the back surface (surface 11S2) of the substrate <NUM> while maintaining the manufacturing yield.

The present technology is applicable to a variety of electronic apparatuses including a semiconductor laser. For example, the present technology is applicable to a light source included in a portable electronic apparatus such as a smartphone, a light source of each of a variety of sensing apparatuses that each sense a shape, an operation, and the like, or the like.

<FIG> is a block diagram illustrating a schematic configuration of a distance measurement system (distance measurement system <NUM>) in which a lighting apparatus <NUM> including the semiconductor laser <NUM> described above is used. The distance measurement system <NUM> measures distance in the ToF method. The distance measurement system <NUM> includes, for example, the lighting apparatus <NUM>, a light receiving unit <NUM>, a control unit <NUM>, and a distance measurement unit <NUM>.

The lighting apparatus <NUM> includes, for example, the semiconductor laser <NUM> illustrated in <FIG> or the like as a light source. The lighting apparatus <NUM> generates illumination light, for example, in synchronization with a light emission control signal CLKp of a rectangular wave. In addition, the light emission control signal CLKp is not limited to the rectangular wave as long as it is a periodic signal. For example, the light emission control signal CLKp may be a sine wave.

The light receiving unit <NUM> receives the reflected light that is reflected from an irradiation target <NUM> and detects, whenever a period of a vertical synchronization signal VSYNC elapses, the amount of light received within the period. For example, a periodic signal of <NUM> hertz (Hz) is used as the vertical synchronization signal VSYNC. In addition, in the light receiving unit <NUM>, a plurality of pixel circuits is disposed in a two-dimensional lattice shape. The light receiving unit <NUM> supplies the image data (frame) corresponding to the amount of light received in these pixel circuits to the distance measurement unit <NUM>. It is to be noted that the frequency of the vertical synchronization signal VSYNC is not limited to <NUM> hertz (Hz), but may be <NUM> hertz (Hz) or <NUM> hertz (Hz).

The control unit <NUM> controls the lighting apparatus <NUM>. The control unit <NUM> generates the light emission control signal CLKp and supplies the lighting apparatus <NUM> and the light receiving unit <NUM> with the light emission control signal CLKp. The frequency of the light emission control signal CLKp is, for example, <NUM> megahertz (MHz). It is to be noted that the frequency of the light emission control signal CLKp is not limited to <NUM> megahertz (MHz), but may be, for example, <NUM> megahertz (MHz).

The distance measurement unit <NUM> measures the distance to the irradiation target <NUM> in the ToF method on the basis of the image data. This distance measurement unit <NUM> measures the distance for each of the pixel circuits and generates a depth map that indicates the distance to the object for each of the pixels as a gradation value. This depth map is used, for example, for image processing of performing a blurring process to the degree corresponding to the distance, autofocus (AF) processing of determining the focused focal point of a focus lens in accordance with the distance, or the like.

Although the present technology has been described above with reference to the embodiment and the application example, the present technology is not limited to the embodiment and the like described above. A variety of modifications are possible. For example, the layer configuration of the semiconductor laser <NUM> described in the embodiment described above is an example and another layer may be further included. In addition, the materials of each of the layers are also examples. Those described above are not limitative.

It is to be noted that the effects described herein are merely illustrative and non-limiting. In addition, other effects may be provided.

Claim 1:
A light emitting device (<NUM>) comprising:
a substrate (<NUM>) including a semi-insulating substrate having a p-type or n-type carrier concentration of <NUM>× <NUM><NUM> cm-<NUM> or less and having a first surface and a second surface that are opposed to each other;
a first contact layer (<NUM>) with a carrier concentration of the first contact layer is <NUM> × <NUM><NUM> cm-<NUM> or more that is stacked on the first surface of the substrate;
a buffer layer (<NUM>) with a carrier concentration of the buffer layer is less than <NUM> × <NUM><NUM> cm-<NUM> and in which at least any of a material composition, and a composition ratio is different from that of the first contact layer, the buffer layer being stacked on the first contact layer (<NUM>); and
a semiconductor stacked body (<NUM>) that is stacked above the first surface of the substrate with the first contact layer (<NUM>) and the buffer layer (<NUM>) interposed in between, the semiconductor stacked body (<NUM>) having a first light reflecting layer (<NUM>), an active layer (<NUM>), a second light reflecting layer (<NUM>) stacked in order from the substrate side and a current confining layer (<NUM>) between the first light reflecting layer (<NUM>) and the active layer (<NUM>), the current confining layer (<NUM>) having a current injection region, the semiconductor stacked body (<NUM>) forming a light emitting region configured to emit laser light, wherein the first contact layer (<NUM>), the buffer layer (<NUM>), and the first light reflecting layer (<NUM>) each include a p-type impurity.