Infrared LED element

Abstract

To improve light-emitting efficiency by enhancing plane-directional light-emitting uniformity in an infra-red LED element having a light-emitting wavelength of 1,000 nm or more.SOLUTION: An infra-red LED element has: a conductive supporting substrate; a reflection layer formed on an upper layer of the supporting substrate, and composed of a metal material; an insulating layer formed on an upper layer of the reflection layer; a contact layer of a first conductivity type formed on an upper layer of the insulating layer, and composed of GaxIn1-xAsyP1-y (0≤x<0.33, 0≤y<0.70); a first clad layer of the first conductivity type formed on an upper layer of the contact layer; an active layer formed on an upper layer of the first clad layer; a second clad layer of a second conductivity type formed on an upper layer of the active layer, and different from the first conductivity type; a first electrode formed at a plurality of positions in the insulating layer penetratingly in a first direction orthogonal to a principal surface of the supporting substrate to connect the contact layer and the reflection layer; and a second electrode formed on an upper layer of the second clad layer.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an infrared LED element, and particularly to an infrared LED element having an emission wavelength of 1000 nm or more.

Background Art

[0002] In recent years, semiconductor light-emitting elements having an emission wavelength in the infrared region of 1000 nm or more have been widely used in applications such as security and surveillance cameras, gas detectors, medical sensors, and industrial equipment.

[0003] A semiconductor light-emitting element having an emission wavelength of 1000 nm or more is generally manufactured by the following procedure. After sequentially epitaxially growing a first conductivity type semiconductor layer, an active layer (sometimes referred to as a "light-emitting layer"), and a second conductivity type semiconductor layer on an InP substrate as a growth substrate, electrodes for current injection are formed on the semiconductor wafer. Thereafter, it is cut into chip form.

[0004] Conventionally, with regard to semiconductor light-emitting elements having an emission wavelength of 1000 nm or more, there has been a history in which the development of semiconductor laser elements has been advanced first. On the other hand, for LED elements, there has been little application, and the development has not progressed as much as that of laser elements.

[0005] However, in recent years, due to the expansion of applications, there has been an increasing demand for products with higher efficiency for infrared LED elements. For example, Patent Document 1 discloses an infrared LED element in which electrodes are formed on the upper and lower surfaces of a wafer in which an LED structure is crystal-grown on an InP substrate, and a current is injected into the active layer by applying a voltage between both electrodes to cause light emission. Further, for example, Patent Document 2 discloses a structure in which a wafer in which an epitaxial semiconductor film of an LED structure is crystal-grown on a growth substrate is bonded to a support substrate via a high-reflection layer, and then the growth substrate is thinned or completely removed to improve the light extraction efficiency.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The inventors of the present invention fabricated and examined a plurality of LED elements having a structure formed by bonding a support substrate, which exhibits high light extraction efficiency as described in Patent Document 2. As a result, in the case of an infrared LED element having an emission wavelength of 1000 nm or more, a phenomenon in which light emission becomes non - uniform inside the LED chip was confirmed. When such a phenomenon occurs, problems such as a decrease in light emission efficiency, current concentration only in a part of the region, and a shortened life occur, which is not preferable.

[0008] In view of the above problems, an object of the present invention is to improve the light emission efficiency by enhancing the uniformity of light emission in the plane direction in an infrared LED element having an emission wavelength of 1000 nm or more.

Means for Solving the Problems

[0009] The infrared LED element according to the present invention has a peak wavelength of 1000 nm or more and 2000 nm or less, and a support substrate exhibiting conductivity, a reflective layer made of a metal material formed on the upper layer of the support substrate, an insulating layer formed on the upper layer of the reflective layer, a contact layer made of Ga x In 1-x As y P 1-y (0 ≦ x < 0.33, 0 ≦ y < 0.70) formed on the upper layer of the insulating layer, a first cladding layer of the first conductivity type formed on the upper layer of the contact layer, an active layer formed on the upper layer of the first cladding layer, A second cladding layer of a second conductivity type different from the first conductivity type, formed on the upper layer of the active layer; In a partial region of the insulating layer, a first electrode formed to penetrate in a first direction orthogonal to the main surface of the support substrate, connecting the contact layer and the reflective layer; It has a second electrode formed on the upper layer of the second cladding layer.

[0010] When manufacturing an infrared LED element with a peak wavelength of 1000 nm or more and 2000 nm or less, an InP substrate is used as a growth substrate, and it is necessary to epitaxially grow a semiconductor layer made of a material lattice-matched to this growth substrate. Examples of such materials include InP, GaInAsP, AlGaInAs, AlInAs, InGaAs, etc.

[0011] In this specification, the "peak wavelength" refers to the wavelength at which the optical output is highest in the emission spectrum. Also, in this specification, the description "GaInAsP" means a mixed crystal of Ga, In, As, and P, and the description of the composition ratio is simply omitted. The same applies to other descriptions such as "AlGaInAs".

[0012] The reflective layer is provided for the purpose of reflecting the light that has traveled from the active layer to the side opposite to the light extraction surface (the second cladding layer side) (the support substrate side) and making it travel to the light extraction surface side. From this perspective, it is composed of a metal material with a high reflectivity for light with a wavelength of 1000 nm to 2000 nm emitted from the active layer. The reflectivity is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. As materials for such a reflective layer, for example, materials such as Ag, Ag alloy, Au, Al, Cu can be used.

[0013] By the way, if the purpose is simply to return the light traveling toward the support substrate side to the light extraction surface side, it might seem advisable to adopt a structure in which the reflective layer is in direct contact with the entire surface of the contact layer. However, in order to reduce the contact resistance between the contact layer made of a semiconductor material and the reflective layer made of a metal material, it is necessary to perform heat treatment on both of them. When heat treatment is performed by bringing into contact a contact layer made of a semiconductor material lattice-matched to InP and a reflective layer made of a metal material, the metal material constituting the reflective layer and the contact layer are alloyed, resulting in a decrease in reflectivity. From such a viewpoint, the reflective layer cannot be directly brought into contact with the contact layer. Therefore, from the viewpoint of ensuring electrical connection between the reflective layer and the contact layer, as in the above structure, a first electrode for connecting the contact layer and the reflective layer is provided.

[0014] The first electrode is made of a material that has a lower reflectivity than the reflective layer but can be easily alloyed with the contact layer to achieve a low contact resistance. As an example, the first electrode can use an AuZn, AuBe, Au / Zn / Au layer structure, etc.

[0015] As described above, since the first electrode has a lower reflectivity than the reflective layer, if the interface electrode is formed almost entirely in the plane direction of the support substrate, the light extraction efficiency will be significantly reduced. For this reason, in the infrared LED element according to the present invention, an insulating layer is provided between the reflective layer and the contact layer, and in a partial region in the plane direction, the first electrode is formed so as to penetrate this insulating layer and connect the contact layer and the reflective layer.

[0016] As insulating layers, SiO2, SiN, Al2O3, etc. can be used. Since these materials have high thermal stability, even if heat treatment is performed for the purpose of reducing the contact resistance between the contact layer and the first electrode, the chemical properties of the insulating layer hardly change. Also, all of these materials exhibit a high transmittance of 90% or more for light with a wavelength of 1000 nm or more and 2000 nm or less. Therefore, the light emitted from the active layer and traveling toward the support substrate side passes through the region in the insulating layer where the first electrode is not formed, and then is reflected by the reflective layer formed thereunder and guided to the light extraction surface.

[0017] From the viewpoint of increasing the light extraction efficiency, it is preferable to make the area of the region where the first electrode is formed as small as possible in the direction parallel to the main surface of the support substrate (hereinafter simply referred to as the "plane direction"). On the other hand, if this area is made too small, the path of the current flowing in the semiconductor layer will concentrate at some points and the resistance will increase. From such a viewpoint, the first electrode is formed at a plurality of discrete locations in the plane direction.

[0018] From the viewpoint of reducing the contact resistance with the first electrode made of a metal material as much as possible, the contact layer is preferably composed of a material having as low a resistivity as possible. Here, among the above-described materials lattice-matched with the InP growth substrate, for materials containing Al such as AlGaInAs and AlInAs, since Al is easily oxidized, the resistivity may increase during manufacturing or during continued use. Also, since the absorption edge wavelength of InGaAs is longer than or close to the peak wavelength, the ratio of the light emitted from the active layer absorbed in the contact layer increases, and high light extraction efficiency cannot be achieved. From such a viewpoint, it is preferable to use InP or GaInAsP as the contact layer included in the infrared LED element according to the present invention.

[0019] Here, according to the intensive research of the present inventors, when an infrared LED element including a contact layer having different Ga and In compositions is manufactured and actually made to emit light, it was confirmed that variations in light emission occur depending on the composition. And the contact layer is Ga x In 1-xAs y P 1-y It has been found that by realizing in the range of (0 ≦ x < 0.33, 0 ≦ y < 0.70), the variation in light emission can be suppressed. This will be described later in the section "Mode for Carrying Out the Invention".

[0020] The total area of the region where the first electrode is formed is preferably 30% or less, more preferably 20% or less, and particularly preferably 15% or less with respect to the area of the active layer.

[0021] According to the above configuration, by reducing the total area of the region where the first electrode is formed, it is possible to suppress a decrease in light extraction efficiency while suppressing the variation in light emission in the plane direction.

[0022] The infrared LED element has a peak wavelength of 1000 nm or more and less than 1200 nm, The contact layer is composed of Ga x In 1-x As y P 1-y and may be composed of (0 ≦ x < 0.14, 0 ≦ y < 0.30).

[0023] Increasing the Ga composition of the contact layer, in other words, increasing the value of x in Ga x In 1-x As y P 1-y causes the wavelength of the absorption edge (the wavelength corresponding to the bandgap energy) to shift to the longer wavelength side. When the wavelength of the absorption edge approaches the peak wavelength, the ratio of the light emitted from the active layer being absorbed by the contact layer increases, which is not preferable from the viewpoint of increasing the light extraction efficiency.

[0024] Therefore, when the peak wavelength of the infrared LED element is 1000 nm or more and less than 1200 nm, it is preferable that the value of x indicating the Ga composition of the contact layer be 0 ≦ x < 0.14.

[0025] As described above, since each semiconductor layer included in the infrared LED element needs to be epitaxially grown using InP as a growth substrate, it is necessary to have a composition lattice-matched to InP. For this reason, when using Ga x In 1-x As y P 1-y (0 ≦ x < 0.33, 0 ≦ y < 0.70), if the Ga composition (value of x) is increased, the As composition (value of y) will inevitably increase as well. Conversely, if the Ga composition (value of x) is decreased, the As composition (value of y) will inevitably decrease. From the perspective of lattice matching, when the value of x indicating the Ga composition is 0 ≦ x < 0.14, it is preferable that the value of y indicating the As composition is 0 ≦ y < 0.30.

[0026] The infrared LED element has a peak wavelength of 1200 nm or more and 2000 nm or less, the contact layer may be made of Ga x In 1-x As y P 1-y (0.14 ≦ x < 0.33, 0.30 ≦ y < 0.70).

[0027] When the peak wavelength is 1200 nm or more and 2000 nm or less, even if the value of x indicating the Ga composition is 0.14 ≦ x < 0.33, it is hardly necessary to consider the light absorption in the contact layer. On the other hand, through intensive research by the inventors, it was confirmed that the contact resistance can be reduced as the Ga composition is increased. From such a perspective, when the peak wavelength is 1200 nm or more and 2000 nm or less, it is preferable to increase the Ga composition to 0.14 ≦ x < 0.33 compared to the case where the peak wavelength is 1000 nm or more and less than 1200 nm. And in this case, from the perspective of lattice matching, it is preferable that the value of y indicating the As composition is 0.30 ≦ y < 0.70.

[0028] From the above viewpoints, it is preferable that the material of the contact layer is selected such that the wavelength of the absorption edge is 100 nm or more shorter than the peak wavelength.

[0029] The first conductivity type may be p-type and the second conductivity type may be n-type.

[0030] In order to increase the light extraction efficiency, a structure in which light is not emitted directly below the electrode (surface electrode) formed on the light extraction surface side is preferable. Specifically, when considering the current path between the second electrode (surface electrode) and the first electrode (interface electrode), by causing current dispersion in the cladding layer on the second electrode side as viewed from the active layer, it becomes possible to suppress light emission directly below the second electrode. In order to realize such a current path, it is necessary that the resistance of the cladding layer on the light extraction side of the active layer, that is, the second cladding layer, is smaller than the resistance of the cladding layer on the reflection film side of the active layer, that is, the first cladding layer. And it is easier to realize a lower resistance for the n-type semiconductor than for the p-type semiconductor. For this reason, by making the second cladding layer, which is on the light extraction surface side, n-type and the first cladding layer p-type, light emission directly below the second electrode can be suppressed, and the light extraction efficiency can be further increased.

Effects of the Invention

[0031] According to the present invention, an infrared LED element having a high uniformity of light emission in the plane direction and an emission wavelength of 1000 nm or more is realized.

Brief Description of the Drawings

[0032]

Figure 1

Figure 2A

Figure 2B

Figure 2C

Figure 2D

Figure 2E

Figure 2F

Figure 3A

Figure 3B

Figure 4A

Figure 4B

Figure 5

Figure 6A

Figure 6B

Embodiments for Carrying Out the Invention

[0033] Embodiments of the infrared LED element according to the present invention will be described with reference to the drawings. Note that the following drawings are schematically shown, and the dimensional ratios on the drawings do not necessarily match the actual dimensional ratios. Also, the dimensional ratios may not match between the drawings.

[0034] In this specification, the expression "layer B is formed on the upper layer of layer A" is intended to include not only the case where layer B is directly formed on the surface of layer A, but also the case where layer B is formed on the surface of layer A via a thin film. Here, the "thin film" refers to a layer with a film thickness of 10 nm or less, and preferably 5 nm or less.

[0035] Figure 1 is a cross-sectional view schematically showing the structure of the infrared LED element of this embodiment. The infrared LED element 1 shown in Figure 1 includes a semiconductor layer 20 formed on the upper layer of a support substrate 11. The infrared LED element 1 shown in Figure 1 corresponds to a schematic cross-sectional view when cut along the XY plane at a predetermined position. In the following description, the XYZ coordinate system attached to Figure 1 is referred to as appropriate.

[0036] In the following description, when distinguishing between positive and negative directions when expressing a direction, it is described with positive and negative signs, such as "+X direction" and "-X direction". When expressing a direction without distinguishing between positive and negative directions, it is simply described as "X direction". That is, in this specification, when simply described as "X direction", both "+X direction" and "-X direction" are included. The same applies to the Y direction and the Z direction.

[0037] In the infrared LED element 1 shown in Figure 1, the infrared light L (L1, L2) generated in the semiconductor layer 20 (more specifically, in the active layer 25 described later) is extracted in the +Y direction with respect to the active layer 25. The infrared light L is light with a peak wavelength of 1000 nm or more and 2000 nm or less.

[0038] [Element Structure] Hereinafter, the structure of the infrared LED element 1 will be described in detail.

[0039] (Support Substrate 11) The support substrate 11 is made of a conductive material, for example, composed of Si, InP, Ge, GaAs, SiC, or CuW. From the viewpoints of heat dissipation and manufacturing cost, Si is preferable. The thickness (length in the Y direction) of the support substrate 11 is not particularly limited, but for example, it is 50 μm or more and 500 μm or less, preferably 100 μm or more and 300 μm or less.

[0040] (Bonding layer 13) The infrared LED element 1 shown in FIG. 1 includes a bonding layer 13. The bonding layer 13 is made of a low-melting-point solder material, for example, composed of Au, Au-Zn, Au-Sn, Au-In, Au-Cu-Sn, Cu-Sn, Pd-Sn, Sn, etc. As will be described later with reference to FIG. 2E, this bonding layer 13 is used to bond the growth substrate 3 on which the semiconductor layer 20 is formed on the upper surface and the support substrate 11. The thickness of the bonding layer 13 is not particularly limited, but for example, it is 0.5 μm or more and 5.0 μm or less, preferably 1.0 μm or more and 3.0 μm or less.

[0041] (Reflection layer 15) The infrared LED element 1 shown in FIG. 1 includes a reflection layer 15 formed on the upper layer of the bonding layer 13. The reflection layer 15 has a function of reflecting the infrared light L2 that travels in the direction of the support substrate 11 (-Y direction) among the infrared light L generated in the active layer 25 and guiding it in the +Y direction. The reflection layer 15 is a conductive material and is composed of a material that exhibits a high reflectivity with respect to the infrared light L. The reflectivity of the reflection layer 15 with respect to the infrared light L is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. When the peak wavelength of the infrared light L is 1000 nm or more and 2000 nm or less, the reflection layer 15 can use a metal material such as Ag, Ag alloy, Au, Al, Cu, etc.

[0042] The thickness of the reflection layer 15 is not particularly limited, but for example, it is 0.1 μm or more and 2.0 μm or less, preferably 0.3 μm or more and 1.0 μm or less.

[0043] (Insulating layer 17) The infrared LED element 1 shown in FIG. 1 includes an insulating layer 17 formed on the upper layer of the reflective layer 15. The insulating layer 17 exhibits electrical insulation and is composed of a material with high transmittance to infrared light L. The transmittance of the insulating layer 17 to infrared light L is preferably 70% or more, more preferably 80% or more, and particularly preferably 90% or more. When the peak wavelength of the infrared light L is 1000 nm or more and 2000 nm or less, materials such as SiO2, SiN, Al2O3, etc. can be used for the insulating layer 17.

[0044] (Semiconductor layer 20) The infrared LED element 1 shown in FIG. 1 has a semiconductor layer 20 formed on the upper layer of the insulating layer 17. The semiconductor layer 20 is composed of a laminate of multiple layers. Specifically, the semiconductor layer 20 includes a contact layer 21, a first cladding layer 23, an active layer 25, and a second cladding layer 27.

[0045] In this embodiment, the contact layer 21 is made of p-type Ga x In 1-x As y P 1-y (0 ≦ x < 0.33, 0 ≦ y < 0.70). That is, in this embodiment, the "first conductivity type" is p-type. A detailed description of the composition of the contact layer 21 will be given later. The thickness of the contact layer 21 is not limited, but for example, it is 10 nm or more and 1000 nm or less, preferably 50 nm or more and 500 nm or less. Also, the p-type dopant concentration of the contact layer 21 is preferably 5×10 17 / cm 3 or more and 3×10 19 / cm 3 or less, and more preferably 1×10 18 / cm 3 or more and 2×10 19 / cm 3 or less.

[0046] In this embodiment, the first cladding layer 23 is formed on the upper layer of the contact layer 21 and is composed of p-type InP. The thickness of the first cladding layer 23 is not limited, but for example, it is 1000 nm or more and 10000 nm or less, preferably 2000 nm or more and 5000 nm or less. The p-type dopant concentration of the first cladding layer 23 is preferably 1×10 17 / cm 3 or more and 3×10 18 / cm 3 or less at a position away from the active layer 25, and more preferably 5×10 17 / cm 3 or more and 3×10 18 / cm 3 or less.

[0047] As the p-type dopant contained in the contact layer 21 and the first cladding layer 23, Zn, Mg, Be, etc. can be used, Zn or Mg is preferable, and Zn is particularly preferable.

[0048] In this embodiment, the active layer 25 is composed of a semiconductor layer formed on the upper layer of the first cladding layer 23. The active layer 25 can generate light of a target wavelength and is appropriately selected from materials that can be epitaxially grown lattice-matched with the growth substrate 3 made of InP. For example, the active layer 25 may have a single-layer structure of GaInAsP, AlGaInAs, or InGaAs, or may have a MQW (Multiple Quantum Well) structure including a well layer made of GaInAsP, AlGaInAs, or InGaAs and a barrier layer made of GaInAsP, AlGaInAs, InGaAs, or InP having a larger bandgap energy than the well layer.

[0049] When the active layer 25 has a single-layer structure, the film thickness of the active layer 25 is 50 nm or more and 2000 nm or less, preferably 100 nm or more and 300 nm or less. When the active layer 25 has a MQW structure, a well layer and a barrier layer with a film thickness of 5 nm or more and 20 nm or less are stacked in a range of 2 cycles or more and 50 cycles or less.

[0050] The active layer 25 may be doped with an n-type or p-type dopant or may be undoped. When doped with an n-type dopant, for example, Si can be used as the dopant.

[0051] In the present embodiment, the second cladding layer 27 is formed on the upper layer of the active layer 25 and is composed of n-type InP. That is, in the present embodiment, the "second conductivity type" is n-type. The thickness of the second cladding layer 27 is not limited, but is, for example, 100 nm or more and 10,000 nm or less, preferably 500 nm or more and 5,000 nm or less. The n-type dopant concentration of the second cladding layer 27 is preferably 1×10 17 / cm 3 or more and 5×10 18 / cm 3 or less, and more preferably 5×10 17 / cm 3 or more and 4×10 18 / cm 3 or less. As the n-type impurity material doped in the second cladding layer 27, Sn, Si, S, Ge, Se, etc. can be used, and Si is particularly preferable.

[0052] The first cladding layer 23 and the second cladding layer 27 are materials that do not absorb the infrared light L generated in the active layer 25 and are appropriately selected from materials that can be epitaxially grown in lattice matching with the growth substrate 3 (see FIG. 2A described later) made of InP. For example, as the first cladding layer 23 and the second cladding layer 27, in addition to InP, materials such as GaInAsP and AlGaInAs can also be used.

[0053] In the example shown in FIG. 1, uneven portions 27a are formed on the +Y side surface of the second cladding layer 27. By forming the uneven portions 27a, the amount of light reflected toward the active layer 25 side on the surface of the second cladding layer 27 is reduced for the infrared light L (L1, L2) traveling in the +Y direction from the active layer 25, and the light extraction efficiency is increased. However, in the present invention, whether or not to provide the uneven portions 27a on the surface of the second cladding layer 27 is optional.

[0054] (First electrode 31) The infrared LED element 1 shown in FIG. 1 has a first electrode 31 formed by penetrating the insulating layer 17 in the Y direction (corresponding to the "first direction") at a plurality of locations within the insulating layer 17. The first electrode 31 connects the contact layer 21 formed on the +Y side of the insulating layer 17 and the reflective layer 15 formed on the -Y side of the insulating layer 17.

[0055] The first electrode 31 is composed of a material capable of making an ohmic contact with the contact layer 21. As an example, the first electrode 31 is composed of materials such as Au / Zn / Au, AuZn, AuBe, etc., and it may have a plurality of these materials. These materials have a lower reflectivity with respect to the infrared light L compared to the material constituting the reflective layer 15.

[0056] The pattern shape of the first electrode 31 when viewed in the Y direction is arbitrary. However, from the viewpoint of flowing current in a wide range within the active layer 25 in the direction parallel to the main surface (XZ plane) of the support substrate 11 (hereinafter referred to as the "plane direction"), it is preferable that a plurality of first electrodes 31 are arranged dispersedly in the plane direction.

[0057] When viewed from the Y direction, the total area of all the first electrodes 31 is preferably 30% or less, more preferably 20% or less, and particularly preferably 15% or less with respect to the area related to the plane direction of the semiconductor layer 20 (for example, the active layer 25). When the total area of the first electrode 31 becomes relatively large, the infrared light L2 traveling from the active layer 25 toward the support substrate 11 side (-Y direction) is absorbed by the first electrode 31, resulting in a decrease in the extraction efficiency. On the other hand, if the total area of the first electrode 31 is too small, the resistance value becomes high and the forward voltage increases.

[0058] (Second electrode 32) The infrared LED element 1 shown in Fig. 1 is provided with a second electrode 32 formed on the upper layer of the second cladding layer 27. The second electrode 32 is preferably formed to extend in a lattice shape in the upper layer of the second cladding layer 27 when viewed in the Y direction. Thereby, the current flowing in the active layer 25 can be spread in the plane direction, and light emission can be achieved in a wide range within the active layer 25. However, in the present invention, the pattern shape of the second electrode 32 is arbitrary.

[0059] As an example, the second electrode 32 is made of a material such as Au / Zn / Au, AuZn, or AuBe, and may include a plurality of these materials.

[0060] (Back surface electrode 33) The infrared LED element 1 shown in Fig. 1 is provided with a back surface electrode 33 formed on the surface on the side opposite to the semiconductor layer 20 (-Y side) of the support substrate 11. An ohmic contact is realized between the back surface electrode 33 and the support substrate 11. As an example, the back surface electrode 33 is made of a material such as AuGe / Ni / Au, Pt / Ti, or Ge / Pt, and may include a plurality of these materials.

[0061] [Manufacturing method] An example of the manufacturing method of the above-described infrared LED element 1 will be described with reference to FIGS. 2A to 2F. FIGS. 2A to 2F are all cross-sectional views in one step in the manufacturing process.

[0062] (Step S1) As shown in Fig. 2A, a growth substrate 3 made of InP is transported into a MOCVD (Metal Organic Chemical Vapor Deposition) apparatus, and a second cladding layer 27, an active layer 25, a first cladding layer 23, and a contact layer 21 are sequentially epitaxially grown on the growth substrate 3 to form a semiconductor layer 20. In this step S1, according to the material and film thickness of the layer to be grown, the type and flow rate of the source gas, the processing time, the environmental temperature, etc. are appropriately adjusted. Examples of the materials of each semiconductor layer 20 are as described above. In particular, the contact layer 21 is Ga x In 1-x As yP 1-y The growth conditions are adjusted so that (0 ≦ x < 0.33, 0 ≦ y < 0.70).

[0063] (Step S2) The epitaxial wafer is taken out from the MOCVD apparatus, and a resist mask patterned by photolithography is formed on the surface of the contact layer 21. Thereafter, a film of the forming material (for example, AuZn) of the first electrode 31 is formed using a vacuum evaporation apparatus, and then the resist mask is peeled off by a lift-off method. Thereafter, for example, annealing treatment is performed by heat treatment at 450°C for 10 minutes, whereby ohmic contact between the contact layer 21 and the first electrode 31 is realized.

[0064] Next, an insulating layer 17 made of, for example, SiO2 is formed by plasma CVD method. Thereafter, by photolithography and etching methods, the insulating layer 17 located above the first electrode 31 is removed, and the first electrode 31 is exposed (see FIG. 2B).

[0065] (Step S3) As shown in FIG. 2C, a bonding layer 13a made of, for example, Au - Sn is formed so as to cover the insulating layer 17 and the first electrode 31. Note that the bonding layer 13a may be configured to be made of the same material as the bonding layer 13.

[0066] (Step S4) As shown in FIG. 2D, a support substrate 11 different from the growth substrate 3 is prepared, and a bonding layer 13b made of, for example, Au - Sn is formed on the upper surface thereof. Although not shown, a metal layer for contact (for example, Ti) may be formed on the surface of the support substrate 11, and the bonding layer 13b may be formed thereon.

[0067] (Step S5) As shown in FIG. 2E, the growth substrate 3 and the support substrate 11 are bonded via the bonding layer 13 (13a, 13b) at a temperature of, for example, 280° C. and a pressure of 1 MPa. By this treatment, the bonding layer 13a on the growth substrate 3 and the bonding layer 13b on the support substrate 11 are melted and integrated (bonding layer 13).

[0068] (Step S6) After applying and protecting a resist on the surface on the semiconductor layer 20 side, a grinding and polishing treatment or a wet etching treatment using a hydrochloric acid-based etchant is performed on the exposed growth substrate 3. Thereby, the growth substrate 3 is peeled off and the second cladding layer 27 is exposed (see FIG. 2F).

[0069] (Step S7) After forming a film of the formation material (for example, AuGe / Ni / Au) of the second electrode 32 on the surface of the exposed second cladding layer 27 using a vacuum deposition apparatus, an alloying treatment (annealing treatment) is performed by heat treatment at, for example, 450° C. for 10 minutes, whereby the second electrode 32 is formed (see FIG. 1).

[0070] (Step S8) Next, wet etching is performed on the surface of the second cladding layer 27 where the second electrode 32 is not formed, and the uneven portion 27a is formed. Thereafter, mesa etching for separating each element is performed. Specifically, wet etching treatment is performed with a mixed solution of bromine and methanol in a state where the non-etching region on the surface of the second cladding layer 27 is masked by a resist patterned by photolithography. Thereby, a part of the semiconductor layer 20 located in the unmasked region is removed (see FIG. 1).

[0071] (Step S9) Next, a film of the formation material (for example, Ti / Au) of the back surface electrode 33 is formed on the -Y side surface of the support substrate 11 using a vacuum deposition apparatus, and the back surface electrode 33 is formed. Thereby, the infrared LED element 1 shown in FIG. 1 is manufactured.

[0072] Note that the execution order of steps S7, S8, and S9 may be changed as appropriate. Also, in other processes, as long as it is within the range that does not affect the manufacturing of the infrared LED element 1, the order may be appropriately changed before and after.

[0073] [Verification] A voltage was applied to cause light emission for a plurality of types of infrared LED elements 1 manufactured according to the above steps S1 to S9 with only the composition of the contact layer 21 being different. At this time, the applied voltage was adjusted so that the current flowing through the infrared LED element 1 became 50 mA.

[0074] Figure 3A is x In 1-x As y P 1-y a graph showing the relationship between the Ga composition (x value) of the contact layer 21 composed of and the forward voltage Vf of the infrared LED element 1. A plurality of infrared LED elements 1 with the same Ga composition (x value) were fabricated, and the forward voltage Vf was measured for each of them.

[0075] Since the contact layer 21 needs to be epitaxially grown on the growth substrate 3 made of InP, it is necessary to be lattice-matched to InP. Due to such circumstances, when the Ga composition (x value) of the contact layer 21 is changed, the As composition (y value) of the contact layer 21 is also inevitably changed. Specifically, in order to achieve lattice matching to InP, when the Ga composition (x value) is increased, the As composition (y value) also needs to be increased. From this perspective, Figure 3B is a graph showing the relationship between the As composition (y value) of the contact layer 21 and the forward voltage Vf of the infrared LED element 1 for the infrared LED element 1 fabricated during the verification of Figure 3A. In addition, in Figures 3A and 3B, for reference, the bandgap wavelength (absorption edge wavelength) of the contact layer 21 determined by the corresponding Ga composition (x value) and As composition (y value) is shown on the upper horizontal axis.

[0076] The infrared LED element with a Ga composition of 0.06 in the contact layer 21 had an As composition of 0.12. That is, the infrared LED element plotted at the location of the Ga composition of 0.06 in Fig. 3A and the infrared LED element plotted at the location of the As composition of 0.12 in Fig. 3B are the same element.

[0077] The correspondence between the Ga composition and the As composition is as follows. The infrared LED element with a Ga composition of 0.15 in the contact layer 21 had an As composition of 0.33. The infrared LED element with a Ga composition of 0.22 in the contact layer 21 had an As composition of 0.48. The infrared LED element with a Ga composition of 0.31 in the contact layer 21 had an As composition of 0.66. The infrared LED element with a Ga composition of 0.33 in the contact layer 21 had an As composition of 0.70. The infrared LED element with a Ga composition of 0.38 in the contact layer 21 had an As composition of 0.83.

[0078] According to Fig. 3A, in the range where the Ga composition of the contact layer 21 is 0.31 or less (the range where the As composition is 0.66 or less), there was little variation in the forward voltage Vf of the infrared LED element 1. On the other hand, in the range where the Ga composition of the contact layer 21 is 0.33 or more (the range where the As composition is 0.70 or more), significant variation was confirmed in the forward voltage Vf of the infrared LED element 1. From this result, it can be seen that from the viewpoint of suppressing the variation in the forward voltage Vf, it is preferable that the Ga composition of the contact layer 21 is less than 0.33 and the As composition is less than 0.70.

[0079] Fig. 4A is a photograph taken with an infrared camera from the light extraction surface side (the second cladding layer 27 side) when a voltage is applied to the infrared LED element 1 manufactured with a Ga composition of 0.38 in the contact layer 21. Fig. 4B is a photograph taken by the above method in the case of the infrared LED element 1 manufactured with a Ga composition of 0.15 in the contact layer 21.

[0080] According to FIG. 4A, when the Ga composition of the contact layer 21 is 0.38, there are regions with high and low emission intensities, and it is confirmed that emission unevenness occurs in the plane direction. On the other hand, according to FIG. 4B, when the Ga composition of the contact layer 21 is 0.15, light is emitted uniformly in the plane direction, and no emission unevenness is confirmed.

[0081] According to the results of FIGS. 3A and 4A, when the Ga composition of the contact layer 21 is 0.38, emission unevenness is confirmed, and there is variation in the forward voltage Vf. From this, it is presumed that when the Ga composition of the contact layer 21 is 0.38, there is variation in the contact resistance between the plurality of first electrodes 31 provided in the plane direction and the contact layer 21. Due to the variation in the contact resistance, among the plurality of first electrodes 31, there are those through which a relatively high current flowed (reference numeral 31a in FIG. 4A) and those through which little current flowed (reference numeral 31b in FIG. 4A). As a result, the emission intensity became high at the locations near the former first electrode 31 (31a), while the emission intensity became low at the locations near the latter first electrode 31 (31b), and it is considered that emission unevenness occurred in the plane direction.

[0082] Also, according to the results of FIGS. 3A and 4B, when the Ga composition of the contact layer 21 is 0.15, there is no variation in the forward voltage Vf, and no emission unevenness is confirmed. From this, it is considered that when the Ga composition of the contact layer 21 is 0.15, there is no variation in the contact resistance between the first electrode 31 and the contact layer 21.

[0083] Based on the results of FIG. 3A, it can be seen that by setting the Ga composition of the contact layer 21 to less than 0.33, the emission variation in the plane direction of the infrared LED element 1 can be suppressed. As described above, the contact layer 21 is made of Ga x In 1-x As y P 1-yWhen configured in this way, when the Ga composition is determined, the As composition is also determined from the perspective of lattice matching. That is, based on the results of FIGS. 3A and 3B, it can be seen that by setting the Ga composition of the contact layer 21 to less than 0.33 and the As composition to less than 0.70, the variation in light emission in the plane direction of the infrared LED element 1 can be suppressed.

[0084] Ga x In 1-x As y P 1-y Although it is not clear why the variation in contact resistance could be suppressed by setting the Ga composition of the contact layer 21 composed of to less than 0.33, the inventors speculate as follows. As described above, in step S2, the contact layer 21 is annealed to achieve ohmic contact with the first electrode 31. This ohmic contact is realized by alloying the first electrode 31 and the contact layer 21. However, it is speculated that the alloy reaction may have become unstable due to the increase in the Ga and As compositions of the materials constituting the contact layer 21.

[0085] FIG. 5 is a graph showing the results of measuring the contact resistance by the TLM (Transmission Line Model) method using an electrode pattern for inspection with respect to the contact layer 21 on the top surface, with the semiconductor layer 20 fabricated with different Ga compositions in step S1, in association with the Ga composition.

[0086] The contact resistance shown in FIG. 5 is substantially different from the contact resistance between the first electrode 31 and the contact layer 21 in the infrared LED element 1. This is because each first electrode 31 has an extremely small diameter (for example, about φ5 to 15 μm), so the contact area with the contact layer 21 is small, whereas in the case of the measurement method using the electrode pattern by the TLM method, the contact area between the contact layer 21 and the TLM pattern is extremely large (for example, 100 to 200 μm square). Therefore, in order to distinguish it from the contact resistance in the infrared LED element 1, it is named "TLM contact resistance" in FIG. 5, and the same term is used in the following description.

[0087] Note that since the diameter of the first electrode 31 is extremely small as described above, it is practically difficult to measure the contact resistance itself between the first electrode 31 and the contact layer 21 in the infrared LED element 1.

[0088] From the results of FIG. 5, it can be seen that as the Ga composition of the contact layer 21 decreases, the TLM contact resistance increases. This result means that in the infrared LED element 1, as the Ga composition of the contact layer 21 decreases, the combined resistance of the contact resistances between the plurality of first electrodes 31 and the contact layer 21 tends to increase. That is, when there is no problem with the variation in the contact resistance between each first electrode 31 and the contact layer 21, it can be seen that it is preferable to increase the Ga composition of the contact layer 21 from the viewpoint of reducing the forward voltage of the infrared LED element 1.

[0089] Note that in the results of FIG. 5, regardless of the value of the Ga composition of the contact layer 21, there is no significant difference in the degree of variation in the TLM contact resistance. This is presumably because the contact area between the contact layer 21 and the TLM electrode pattern is large, so even if there is variation in the contact resistance in the microscopic region, it hardly affects the resistance value in the contact region between the entire electrode pattern for TLM and the contact layer 21.

[0090] On the other hand, since the diameter of the first electrode 31 provided in the actual infrared LED element 1 is small as described above, the variation in the contact resistance in the microscopic region directly affects the contact resistance between the first electrode 31 and the contact layer 21. Explaining this in correspondence with the photograph of FIG. 4A, when the contact resistance between one first electrode 31b and the contact layer 21 is larger than the contact resistance between another first electrode 31a and the contact layer 21, a difference in the current density flowing depending on the location will occur.

[0091] In view of the results of FIG. 5, from the viewpoint of suppressing the variation in the contact resistance between each first electrode 31 and the contact layer 21 and reducing the forward voltage Vf, it can be seen that the Ga composition of the contact layer 21 is preferably greater than 0.13 and less than 0.33. Considering the results of FIG. 3 as well, it can be seen that the Ga composition of the contact layer 21 is preferably 0.14 or more and 0.31 or less.

[0092] By the way, when the Ga composition of the contact layer 21 is changed, the absorption edge wavelength λ0 (bandgap wavelength) of the contact layer 21 shifts. When the peak wavelength λ L of the infrared light L is close to the absorption edge wavelength λ0 of the contact layer 21, the contact layer 21 absorbs most of the infrared light L and the light extraction efficiency decreases. From this viewpoint, the Ga composition of the contact layer 21 is preferably set so that the absorption edge wavelength λ0 of the contact layer 21 is on the shorter wavelength side by 100 nm or more than the peak wavelength λ L of the infrared light L. FIGS. 6A and 6B are examples of the spectra of the infrared LED element 1 manufactured according to the above steps S1 to S9. Each infrared LED element 1 changes the peak wavelength λ L by varying the composition of the active layer 25.

[0093] As shown in FIG. 6A, in the case of the infrared LED element 1 with a peak wavelength λ L of 1050 nm, the Ga composition of the contact layer 21 is preferably set so that the absorption edge wavelength λ0 of the contact layer 21 is less than 950 nm. Further, as shown in FIG. 6B, in the case of the infrared LED element 1 with a peak wavelength λ L of 1200 nm, the Ga composition of the contact layer 21 is preferably set so that the absorption edge wavelength λ0 of the contact layer 21 is less than 1100 nm.

[0094] In other words, when the peak wavelength λ L is 1000 nm or more and less than 1200 nm, the Ga composition of the contact layer 21 is preferably less than 0.14. On the other hand, the peak wavelength λ LWhen it is 1200 nm or more and 2000 nm or less, the Ga composition of the contact layer 21 is preferably 0.14 or more and less than 0.33.

[0095] [Another Embodiment] In the above embodiment, the first conductivity type is p-type and the second conductivity type is n-type, but the conductivity types may be reversed. That is, in the infrared LED element 1 shown in FIG. 1, the contact layer 21 and the first clad layer 23 may be n-type and the second clad layer 27 may be p-type.

Explanation of Reference Numerals

[0096] 1: Infrared LED element 3: Growth substrate 11: Support substrate 13: Bonding layer 13a: Bonding layer 13b: Bonding layer 15: Reflective layer 17: Insulating layer 20: Semiconductor layer 21: Contact layer 23: First clad layer 25: Active layer 27: Second clad layer 27a: Concavo-convex portion 31, 31a, 31b: First electrode 32: Second electrode 33: Back electrode L, L1, L2: Infrared light

Claims

1. An infrared LED element having a peak wavelength of 1000 nm or more and 2000 nm or less, a supporting substrate that exhibits electrical conductivity; a reflective layer made of a metal material formed on the support substrate; an insulating layer formed on the reflective layer; A first conductivity type Ga formed on the insulating layer. x In 1-x As y P 1-y a contact layer consisting of (0≦x<0.33, 0≦y<0.70); a first clad layer of the first conductivity type formed on the contact layer; an active layer formed on the first cladding layer; a second clad layer of a second conductivity type different from the first conductivity type formed on the active layer; a first electrode formed at a plurality of locations within the insulating layer so as to penetrate the insulating layer in a first direction perpendicular to the main surface of the support substrate, the first electrode connecting the contact layer and the reflective layer; a second electrode formed on the second clad layer, The infrared LED element, wherein the first electrode is made of a metal material having a reflectivity for light emitted from the active layer lower than that of the reflective layer.

2. 2. The infrared LED element according to claim 1, wherein the total area of the region where the first electrodes are formed is 30% or less of the area of the active layer.

3. The peak wavelength is 1000 nm or more and less than 1200 nm, The contact layer is Ga x In 1-x As y P 1-y 3. The infrared LED element according to claim 1, wherein x is a number greater than or equal to 0.14, y is a number less than or equal to 0.

30.

4. The peak wavelength is 1200 nm or more and 2000 nm or less, The contact layer is Ga x In 1-x As y P 1-y 3. The infrared LED element according to claim 1, wherein x is a number between 0.14 and 0.33, and y is a number between 0.30 and 0.

70.

5. 5. The infrared LED element according to claim 1, wherein the wavelength of the absorption edge of the contact layer is shorter than the peak wavelength by 100 nm or more.

6. 6. The infrared LED element according to claim 1, wherein the first conductivity type is p-type and the second conductivity type is n-type.

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