Infrared detection element, manufacturing method thereof, and infrared detection device

Abstract

To provide a highly-sensitive infrared detection element which is inexpensive and which has little dark current.SOLUTION: A first electrode layer, a first semiconductor layer, a buffer layer, a second semiconductor layer, and a second electrode are sequentially stacked. A band gap of the first semiconductor layer is wider than that of the second semiconductor layer. The buffer layer has a grating constant within the range of 99% of a grating constant of the first semiconductor layer and 101% of a grating constant of the second semiconductor layer, and is a layer for buffering 80% or more of a grating mismatch of the grating constant of the first semiconductor layer and the second semiconductor layer. Conductive types of the first and second semiconductor layers are similar, and the second semiconductor includes InX (X is an element of group 5).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an infrared detection element, a manufacturing method thereof, and an infrared detection device. [Background technology]

[0002] Infrared detection devices are used in gas sensors, human sensors, heat source monitoring sensors, night vision cameras, etc., and demand for them is expected to continue to increase in the future.

[0003] Current infrared detection devices mainly use semiconductors such as InAs that have a narrow band gap suitable for infrared light and absorb light in that wavelength range, and form a pn junction in the semiconductor to extract electricity through photoelectric conversion. However, cost is an issue that prevents further widespread use of these devices. One of the main reasons for this is that in order to suppress dark current and perform photoelectric conversion efficiently, a high-quality semiconductor substrate such as InAs with few defects is required.

[0004] For this reason, Patent Document 1, for example, discloses a method for reducing the cost of substrates by using a general-purpose substrate such as GaAs and forming a buffer layer such as lattice-relaxed In(Ga)As on it to create a pseudo-substrate, and then forming an InAs pn junction. However, as disclosed in Non-Patent Document 1, this method has the problem that the dark current tends to increase due to the formation of defects associated with lattice relaxation. Furthermore, a method of growing a thick film on the order of microns to reduce the defect density is disclosed in, for example, Non-Patent Document 2, but this thick film formation method has the problem of increasing costs. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-16280 [Non-patent literature]

[0006] [Non-Patent Document 1] Optimized InAlAs graded buffer and tensile-strained dislocation filter layer for high quality InAs photodetector grown on Si, Appl. Phys. Lett., 117, 262106(2020). [Non-patent document 2] Extended wavelength InGaAs on GaAs using InAlAs buffer for back-side-illuminated short-wave infrared detectors, Appl. Phys. Lett.,82,2838(2003). Summary of the Invention [Problem to be solved by the invention]

[0007] An object of the present invention is to provide an infrared detection element and an infrared detection device that are inexpensive, have a small dark current, and have high sensitivity. [Means for solving the problem]

[0008] The configuration of the present invention to solve the problems is shown below. (Configuration 1) a first electrode layer, a first semiconductor layer, a buffer layer, a second semiconductor layer, and a second electrode layer are sequentially stacked; the band gap of the first semiconductor layer is wider than the band gap of the second semiconductor layer; the buffer layer has a lattice constant in the range of 99% of the lattice constant of the first semiconductor layer and 101% of the lattice constant of the second semiconductor layer, and is a layer that alleviates 80% or more of the lattice mismatch between the lattice constant of the first semiconductor layer and the lattice constant of the second semiconductor layer; the first semiconductor layer and the second semiconductor layer have the same conductivity type; The infrared detection element, wherein the second semiconductor layer contains InX (X is an element of Group 5). (Configuration 2) 2. The infrared detection element according to claim 1, wherein the first semiconductor layer is GaAs or Si. (Configuration 3) 3. The infrared detection element according to claim 2, wherein the first semiconductor layer is GaAs(111). (Configuration 4) 3. The infrared detection element according to claim 2, wherein the first semiconductor layer is GaAs(100). (Configuration 5) 5. The infrared detection element according to any one of configurations 1 to 4, wherein X is at least one selected from the group consisting of As and Sb. (Configuration 6) 6. The infrared detection element according to any one of configurations 1 to 5, wherein the buffer layer is made of the same material as the second semiconductor layer. (Configuration 7) 2. The infrared detection element according to claim 1, wherein the first semiconductor layer is made of GaAs(100), the buffer layer is made of GaSb, and the second semiconductor layer is made of InAs. (Configuration 8) 8. The infrared detection element of any one of configurations 1 to 7, wherein the first semiconductor layer and the second semiconductor layer contain a dopant. (Configuration 9) 9. The infrared detection element according to configuration 8, wherein the dopant of the first semiconductor layer is one or more selected from the group consisting of Si, S, As, and P when the first semiconductor layer is n-type. (Configuration 10) 9. The infrared detection element according to configuration 8, wherein the dopant of the first semiconductor layer is one or more selected from the group consisting of Zn, Be, C, B, and Al when the first semiconductor layer is p-type. (Configuration 11) 9. The infrared detection element according to configuration 8, wherein the dopant of the second semiconductor layer is one or more selected from the group consisting of Si, S, Te, and C when the first semiconductor layer is n-type. (Configuration 12) 9. The infrared detection element according to configuration 8, wherein the dopant of the second semiconductor layer is one or more selected from the group consisting of Zn, Be, C, and Ge when the first semiconductor layer is p-type. (Configuration 13) The amount of dopant in the first semiconductor layer and the second semiconductor layer is 2×10 16 / cm 3 More than 1×10 19 / cm 3 13. The infrared detection element according to any one of configurations 8 to 12, wherein: (Configuration 14) 14. The infrared detection element according to any one of configurations 1 to 13, wherein the second semiconductor layer has a thickness of 50 nm or more and 10 μm or less. (Configuration 15) 15. The infrared detection element according to any one of configurations 1 to 14, wherein the buffer layer has a thickness of 0.2 nm to 50 nm. (Configuration 16) 16. The infrared detection element of any one of structures 1 to 15, wherein the first electrode layer and the second electrode layer are made of one or more metals selected from the group consisting of Al, Ti, W, Pt, Au, Ag, Cu, Ru, Rh, Pd, Ni, Sn, Zn, Ge, and In, an alloy containing the metal, a compound containing the metal, poly-Si, or graphite. (Configuration 17) Providing a first semiconductor layer; forming a buffer layer on a first main surface of the first semiconductor layer by MBE or MOCVD; forming a second semiconductor layer on the buffer layer by MBE or MOCVD; forming an electrode layer on at least a portion of a second main surface of the first electrode layer; forming a second electrode layer on at least a portion of the second semiconductor layer; the band gap of the first semiconductor layer is wider than the band gap of the second semiconductor layer; the first semiconductor layer and the second semiconductor layer have the same conductivity type; the buffer layer has a lattice constant in the range of 99% of the lattice constant of the first semiconductor layer and 101% of the lattice constant of the second semiconductor layer, and alleviates 80% or more of the lattice mismatch between the lattice constant of the first semiconductor layer and the lattice constant of the second semiconductor layer; The method for manufacturing an infrared detection element, wherein the second semiconductor layer contains InX (X is an element of Group 5). (Configuration 18) 17. An infrared detection device comprising the infrared detection element according to any one of configurations 1 to 16, and having a circuit in which a DC power supply and an ammeter are electrically connected in series between the first electrode layer and the second electrode layer. [Effects of the Invention]

[0009] According to the present invention, it is possible to provide an infrared detection element and an infrared detection device that are inexpensive, have a small dark current, and have high sensitivity. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a cross-sectional view showing a main structure of an infrared detection element of the present invention. [Figure 2] 1 is an explanatory diagram illustrating a configuration of an infrared detection element of the present invention. [Figure 3] FIG. 2 is a characteristic diagram showing an energy band state of the infrared detection element of the present invention. [Figure 4] FIG. 2 is a flowchart showing the manufacturing process of the infrared detection element of the present invention. [Figure 5] FIG. 1 is an explanatory diagram illustrating a configuration of an infrared detection element according to a first embodiment. [Figure 6] 1 is a cross-sectional TEM photograph of a first semiconductor layer, a buffer layer, and a second semiconductor layer portion of Example 1. [Figure 7] 1 is an optical microscope photograph showing the appearance of the infrared detection element produced in Example 1. [Figure 8] FIG. 2 is a characteristic diagram showing the current-voltage characteristics at 77 K of the infrared detection element fabricated in Example 1. [Figure 9] FIG. 2 is a characteristic diagram showing the temperature dependence of the infrared detection element produced in Example 1. [Figure 10]FIG. 2 is a characteristic diagram showing the spectral sensitivity characteristics of the infrared detection element fabricated in Example 1. [Figure 11] FIG. 2 is a characteristic diagram showing the infrared detection characteristics of the infrared detection element fabricated in Example 1. [Figure 12] FIG. 10 is an explanatory diagram showing the configuration of an infrared detection element according to a second embodiment. [Figure 13] FIG. 10 is a characteristic diagram showing the temperature dependence of the infrared detection element produced in Example 2. [Figure 14] FIG. 10 is an explanatory diagram showing the configuration of an infrared detection element according to a third embodiment. [Figure 15] FIG. 10 is a characteristic diagram showing the spectral sensitivity characteristics at room temperature of the infrared detection element fabricated in Example 3. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] <Structure and Operation> The infrared detection element of the present invention is an element in which an inexpensive and versatile GaAs or Si substrate is used as a first semiconductor layer, and a buffer layer made of InAs or the like that is substantially lattice-relaxed at the interface with the first semiconductor layer is disposed thereon, and a second semiconductor layer made of a narrow-gap semiconductor that corresponds to the infrared absorption band and that is made of InAs or the like is disposed on top of the buffer layer. The buffer layer is a thin, inexpensive film that tolerates defects and utilizes them. The buffer layer on the second semiconductor layer side can easily be made low in lattice defects, so the second semiconductor layer formed on top of it can also easily be made low in defects. By utilizing the large band gap offset between the first and second semiconductor layers, it is possible to provide an inexpensive infrared detector with low dark current and high sensitivity, as described in detail below. The wavelength band of infrared light that is the subject of the present invention is from 1 μm to 6 μm.

[0013] As shown in FIG. 1, the infrared detection element 101 of the present invention includes a first electrode layer 11, a first semiconductor layer 12, a buffer layer 13, a second semiconductor layer 14, and a second electrode layer 15.

[0014] The first electrode layer 11 may be made of any material with high conductivity, preferably one that can form ohmic contact with the first semiconductor layer 12. Examples of materials include one or more metals selected from the group consisting of aluminum (Al), titanium (Ti), tungsten (W), platinum (Pt), gold (Au), silver (Ag), copper (Cu), ruthenium (Ru), rhodium (Rh), palladium (Pd), nickel (Ni), tin (Sn), zinc (Zn), germanium (Ge), and indium (In), alloys containing these metals, compounds containing these metals, polysilicon, and graphite. The first electrode layer 11 may be a single-layer or multilayer film made of these materials. For example, an Au / Ti film is preferably used, in which Ti, acting as an adhesive layer, is in contact with the first semiconductor layer 12. The thickness of the first electrode layer 11 is not particularly limited, but may be, for example, 50 nm to 1 μm.

[0015] The first semiconductor layer 12 is made of a semiconductor whose band gap is wider than the band gap of the second semiconductor layer 14 that absorbs infrared light in the target wavelength band and generates electricity through photoelectric conversion. Furthermore, the first semiconductor layer is preferably inexpensive, has few defects, and is of high quality, so gallium arsenide (GaAs) and silicon (Si) are preferred. GaAs substrates and Si substrates (wafers) are particularly preferred because they have little in-plane and lot-to-lot quality variation, are versatile, and are low cost. A single-crystal semiconductor is preferably used as the first semiconductor layer 12. By using a single-crystal first semiconductor layer 12, the crystallinity of the second semiconductor layer 14 is improved, the infrared detection sensitivity is improved, and dark current can also be reduced.

[0016] The crystal plane orientation of the first semiconductor layer 12 is preferably (111) or (100), for example, GaAs(111) or GaAs(100). Specific examples include: (1) a combination of GaAs(111)A as the first semiconductor layer 12, InSb as the buffer layer 13, and InAs as the second semiconductor layer 14; (2) a combination of Si(111) as the first semiconductor layer 12, InAs as the buffer layer 13, and InAs as the second semiconductor layer 14; and (3) a combination of GaAs(100) as the first semiconductor layer 12, GaAs as the buffer layer 13, and InAs as the second semiconductor layer 14. These combinations enable the infrared detection element 101 to achieve high detection sensitivity while suppressing dark current.

[0017] When a GaAs substrate or a Si substrate is used as the first semiconductor layer, it is preferable to use a low-resistance substrate with low electrical resistance. By using a low-resistance substrate, the internal resistance of the infrared detection element 101 is reduced, and the output of infrared detection can be increased. The substrate resistance should be a sheet resistance of 1×10 -4 ohm cm or more 1×10 -1 A value of ohm·cm or less is preferred. The thickness of the first semiconductor layer 12 is not particularly limited, but can be, for example, 50 nm or more and 1 μm or less.

[0018] The buffer layer 13 has a lattice constant in the range of 99% of the lattice constant of the first semiconductor layer 12 and 101% of the lattice constant of the second semiconductor layer 14, and is a layer that alleviates 80% or more of the lattice mismatch between the lattice constant of the first semiconductor layer 12 and the lattice constant of the second semiconductor layer 14. Here, it is also preferable that buffer layer 13 is made of the same material as second semiconductor layer 14. For example, when indium arsenide (InAs) is used as second semiconductor layer 14, it is preferable that buffer layer 13 is also made of InAs. Using the same material improves manufacturing efficiency and enables cost reduction, and also makes second semiconductor layer 14 disposed on buffer layer 13 a high-quality layer with few defects, thereby improving infrared detection sensitivity and detection stability. The buffer layer 13 may be a single layer film or a laminated film made up of multiple layers. Gallium antimonide (GaSb) can also be used for the buffer layer 13. For example, by using GaAs(111) for the first semiconductor layer 12, GaSb for the buffer layer 13, and InAs for the second semiconductor layer 14, the infrared detection element 101 can achieve high detection sensitivity while suppressing dark current. Note that the lattice constant of InAs is 6.0583, and the lattice constant of GaSb is 6.09593.

[0019] In the buffer layer 13 having this configuration, defects in the buffer layer 13 are concentrated near the interface with the first semiconductor layer 12, and by making the thickness of the buffer layer 13 0.2 nm or more, the lattice defects at the interface on the side in contact with the second semiconductor layer 14 are reduced to a negligible level. This makes it possible to make the second semiconductor layer 14 formed on the buffer layer 13 a high-quality semiconductor with few defects. Although there is no particular upper limit to the thickness of the buffer layer 13, it is preferable to set it to 50 nm or less from the viewpoint of reducing the film formation time and costs.

[0020] The second semiconductor layer 14 is a layer that absorbs infrared rays, causes photoelectric conversion, and generates electromotive force. It is a high-quality semiconductor layer with few defects that has a narrow band gap corresponding to the target infrared wavelength band, and is made of a semiconductor containing InX (X is a group 5 element). In particular, the semiconductor material is InAs, indium antimony (InSb), or a mixed crystal thereof, indium antimony arsenide (InAs 1-α Sb α (α is 0 or more and 1 or less) is preferably used. Therefore, the target Group 5 element (X) can be one or more elements selected from the group consisting of arsenic (As) and antimony (Sb). Here, the band gap of InAs is 0.35 eV (room temperature), which is suitable for the infrared wavelength range of 1 μm to 3.0 μm, and the band gap of InSb is 0.18 eV (room temperature), which is suitable for the infrared wavelength range of 1 μm to 6.0 μm. InAs 1-α Sb α is suitable for the infrared wavelength range with a lower limit of 1 μm and an upper limit of 3.0 μm to 6.0 μm. As described above, the second semiconductor layer 14 is formed in contact with the buffer layer 13, so that the second semiconductor layer 14 can easily become a high-quality semiconductor with few defects.

[0021] What is essential for the infrared detection element 101 of the present invention is that the first semiconductor layer 12 and the second semiconductor layer 14 have the same conductivity type. Here, the same conductivity type means that when the first semiconductor layer 12 is n-type, the second semiconductor layer 14 is also n-type, and when the first semiconductor layer 12 is p-type, the second semiconductor layer 14 is also p-type. The conductivity type is adjusted by incorporating dopants into the semiconductor layer, preferably introduced during the growth of the semiconductor layer.

[0022] The dopant of the first semiconductor layer 12 can be one or more selected from the group consisting of Si, sulfur (S), As, and phosphorus (P) when the first semiconductor layer 12 is n-type, or one or more selected from the group consisting of Zn, beryllium (Be), carbon (C), boron (B), and Al when the first semiconductor layer 12 is p-type. The dopant of the second semiconductor layer 14 can be one or more selected from the group consisting of Si, S, tellurium (Te), and C when the first semiconductor layer 12 is n-type, or one or more selected from the group consisting of Zn, Be, C, and germanium (Ge) when the first semiconductor layer 12 is p-type. The dopant concentration in the first semiconductor layer 12 and the second semiconductor layer 14 is 2×10 16 / cm 3 More than 1×10 19 / cm 3 The following can be mentioned: By satisfying these dopant conditions, the infrared detection element 101 becomes an element that can suppress dark current and obtain high detection sensitivity.

[0023] The thickness of the second semiconductor layer 14 is preferably 50 nm or more and 10 μm or less. When the thickness of the second semiconductor layer 14 is 50 nm or more, infrared rays are sufficiently absorbed, making it possible to obtain high detection sensitivity. There is no particular upper limit to the thickness of the second semiconductor layer 14, but from the viewpoint of reducing the film formation time and cost, it is preferably 10 μm or less.

[0024] The second electrode layer 15 may be made of any material with high conductivity, preferably one that can form ohmic contact with the second semiconductor layer 14. Examples of suitable materials include one or more metals selected from the group consisting of Al, Ti, W, Pt, Au, Ag, Cu, Ru, Rh, Pd, Ni, Sn, Zn, Ge, and In, alloys containing such metals, compounds containing such metals, poly-Si, and graphite. The second electrode layer 15 may be a single-layer or multilayer film made of such materials. For example, an Au / Ti film is preferred, in which Ti, acting as an adhesive layer, is formed in contact with the second semiconductor layer 14. The thickness of the second electrode layer 15 is not particularly limited, but may be, for example, 50 nm or more and 1 μm or less. The second electrode layer 15 preferably has an opening through which infrared light entering the infrared detection element 101 passes.

[0025] The configuration of the main part of the infrared detection device 102 is shown in FIG. Infrared detection device 102 is configured such that an ammeter 21 and a voltage source (DC power supply) 22 are connected in series between first electrode layer 11 and second electrode layer 15 of infrared detection element 101, which includes first electrode layer 11, first semiconductor layer 12, buffer layer 13, second semiconductor layer 14, and second electrode layer 15, by electrical wiring 23, and a bias is applied between first semiconductor layer 12 and second semiconductor layer 14 by voltage source (DC power supply) 22. Here, the ammeter may be replaced with a current output terminal, and the output may be monitored according to the magnitude of the current extracted from there, or devices, equipment, components, etc. electrically connected to infrared detection device 102 may be controlled. Here, ammeter 21 refers to a component or device that reacts according to the current flowing through ammeter 21, and is not limited to a simple ammeter.

[0026] The operating principle of the infrared output device 102 of the present invention will be described with reference to the energy state diagram of FIG. 3. Here, FIG. 3(a) shows an example in which the conductivity type of the first semiconductor layer 12 and the second semiconductor layer 14 is n-type, specifically, n-GaAs is used as the first semiconductor layer 12, InAs is used as the buffer layer 13 disposed near the location indicated as the interface, and n-InAs is used as the second semiconductor layer 14. Also, FIG. 3(b) shows an example in which the conductivity type of the first semiconductor layer 12 and the second semiconductor layer 14 is p-type, specifically, p-GaAs is used as the first semiconductor layer 12, InAs is used as the buffer layer 13 disposed near the location indicated as the interface, and p-InAs is used as the second semiconductor layer 14.

[0027] First, the case where the conductivity type is n-type will be explained with reference to FIG. The band gap g of the n-GaAs of the first semiconductor layer 12 n1 is the band gap g of the n-InAs second semiconductor layer 14. n2 The band gap g is larger than the band gap g n2 is the band gap g n1 That is, the conduction band level of the n-GaAs first semiconductor layer 12 is lower than that of the n-InAs second semiconductor layer 14. n3 The valence band level of the first semiconductor layer 12 is located at a higher position than that of the second semiconductor layer 14 .

[0028] When a forward bias is applied between the first electrode layer 11 and the second electrode layer 15, the band bending of n-GaAs and n-InAs acts as a barrier to the conduction band, so that almost no current flows until a high voltage is applied, thereby significantly suppressing dark current. When infrared light is irradiated while a voltage is applied, the light absorbed in the n-InAs generates electron-hole pairs, and the electric field causes the electrons to move toward the n-InAs surface and the holes to move toward the n-GaAs interface. Because there is also a large barrier in the valence band, the holes accumulate on the n-InAs side near the interface. This pushes the band near the interface downward, effectively lowering the barrier and allowing electrons to move from the n-GaAs to the n-InAs. The electrons injected into the n-InAs side recombine with the holes there and disappear, resulting in current flow.

[0029] Based on the above operating principle, the infrared output device 102 of the present invention has a large band bending of a wide-gap semiconductor compared to a pn junction of a general narrow-gap semiconductor, and functions as a large barrier, making it possible to realize an element with low dark current. Furthermore, since the infrared output device 102 of the present invention is a device composed only of n-type semiconductors, even if defects are formed in the InAs light absorption layer, this does not lead to a significant increase in dark current as occurs in a normal pn junction. Furthermore, electrons tunneling through the barrier on the conduction band side are trapped by defects formed in the band bending region, i.e., trapped in the level formed by the defects, and consumed by recombination, thereby suppressing dark current.

[0030] From the above, an infrared detection device 102 is provided which has an inexpensive structure including a first semiconductor layer 12 which is made of a general-purpose, inexpensive material but which has high quality in terms of defects, a buffer layer 13 which can be easily and inexpensively formed with a thin film thickness by concentrating defects in the vicinity of the first semiconductor layer 12, and a first semiconductor layer 14 which can be easily and inexpensively formed on the buffer layer 13, and which has low dark current and high sensitivity. If the energy state of the material itself places the conduction band level of the first semiconductor layer 12 at a higher position than that of the second semiconductor layer 14, it is not necessarily necessary to apply a bias, and therefore it is possible to provide a low-cost infrared detection device by omitting the DC power supply 22. Even in this case, however, being able to apply a bias has the advantage of making it easier to adjust the infrared detection sensitivity.

[0031] Next, the case where the conductivity type is p-type will be explained with reference to FIG. The band gap g of the p-GaAs of the first semiconductor layer 12 p1 is the band gap g of the p-InAs second semiconductor layer 14. p2 The band gap g is larger than the band gap g p2 is the band gap g p1 That is, the conduction band level of the p-GaAs first semiconductor layer 12 is positioned higher than that of the p-InAs second semiconductor layer 14, and the valence band level of the first semiconductor layer 12 is positioned lower than that of the second semiconductor layer 14 (although they appear to be at the same level in the figure, they are actually slightly lower). Band bending occurs near the boundary between the first semiconductor layer 12 and the second semiconductor layer 14, which is shown as the interface, forming a barrier, but holes generated in the second semiconductor layer 14 by photoelectric conversion when infrared light is incident overcome the barrier and a flow of holes occurs.

[0032] From the above, an infrared detection device 102 is provided which has an inexpensive structure including a first semiconductor layer 12 which is made of a general-purpose, inexpensive material but which has high quality in terms of defects, a buffer layer 13 which can be easily and inexpensively formed with a thin film thickness by concentrating defects in the vicinity of the first semiconductor layer 12, and a first semiconductor layer 14 which can be easily and inexpensively formed on the buffer layer 13, and which has low dark current and high sensitivity.

[0033] <Manufacturing method> A method for manufacturing the infrared detection element 101 will be described with reference to the flowchart of FIG.

[0034] First, the first semiconductor layer 12 is prepared (step S11). Here, a GaAs substrate or a Si substrate can be preferably used as the first semiconductor layer 12. In addition, to reduce the resistance of the first semiconductor layer 12, it is preferable to use a substrate doped with a dopant such as Si. The first electrode layer 11 can be preferably formed by a physical deposition method such as sputtering or evaporation, a CVD (Chemical Vapor Deposition) method, a coating method, or the like.

[0035] Next, a buffer layer 13 is formed on the first main surface (surface) of the first semiconductor layer 12 by MBE (Molecular Beam Epitaxy) or MOCVD (Metal Organic Chemical Vapor Deposition) so that the buffer layer 13 has a lattice constant in the range of 99% of the lattice constant of the first semiconductor layer 12 and 101% of the lattice constant of the second semiconductor layer 14, and alleviates 80% or more of the lattice mismatch between the lattice constants of the first semiconductor layer 12 and the second semiconductor layer 14 (step S12). Here, the buffer layer 13 is preferably made of an intrinsic material that does not contain a dopant. By using an undoped material, it is possible to suppress the dark current of the infrared detection element 101.

[0036] Thereafter, a second semiconductor layer 14 is formed on the buffer layer 13 by MBE or MOCVD (step S13). Here, the second semiconductor layer 14 is InX (X is a group 5 element), the band gap of the first semiconductor layer 12 is wider than the band gap of the second semiconductor layer 14, and the conduction types of the first semiconductor layer 12 and the second semiconductor layer 14 are made the same by doping. As or Sb can be preferably used as X.

[0037] Thereafter, a first electrode layer 11 is formed on the second main surface (rear surface) of the first semiconductor layer 12 (step S14). The first electrode layer 11 can be formed by a physical deposition method such as sputtering or vapor deposition, a CVD method, or a coating method. After depositing the first electrode layer 11 on the second main surface (rear surface) of the first semiconductor layer 12, it is preferable to perform a heat treatment for the purposes of improving adhesion, reducing contact resistance, and improving reliability. This heat treatment is performed at a temperature that does not damage the first semiconductor layer 12, the second semiconductor layer 14, and the first electrode layer 11, for example, 300°C or higher and 450°C or lower. Finally, the second electrode layer 15 is formed on the second semiconductor layer 14 (step S15) to manufacture the infrared detection element 101. The second electrode layer 15 can be preferably formed by a physical deposition method such as a sputtering method or a vapor deposition method, a CVD method, a coating method, or the like.

[0038] In the method for manufacturing the infrared detection element 101 of the present invention, it is not necessary to use an expensive substrate such as InAs or GaSb, and a general-purpose semiconductor with a large band gap such as GaAs can be used, resulting in low costs. Furthermore, the lattice-relaxed structure created by dislocations at the interface can be used, eliminating the need for a thick buffer layer as in the past, which simplifies the device structure and reduces costs. Therefore, the infrared detection element 101 manufactured by the above process is characterized by being inexpensive, having a small dark current, and having high infrared detection sensitivity. [Example]

[0039] Example 1 In Example 1, an infrared detection element having the structure shown in FIG. 5 was fabricated and its characteristics were evaluated.

[0040] <Sample preparation> As shown in FIG. 5, an n-type GaAs (111) A substrate was prepared as the first semiconductor layer 12, and a 1×10 18 / cm 3 Silicon-doped n-type GaAs was grown.

[0041] Next, a 10-nm thick first buffer layer consisting of undoped GaAs was grown, and then the substrate temperature was lowered to 460°C, and a 5-atom-equivalent undoped InAs second buffer layer was grown. It was confirmed that the dark current was reduced by using undoped first and second buffer layers. Continued, 5×10 17 / cm 3 An n-type InAs light absorption layer doped with Si was grown to a thickness of 300 nm to form the second semiconductor layer 14. Here, the lattice mismatch between the lattice constant of the first semiconductor layer and the lattice constant of the second semiconductor layer was alleviated by 90% by the first and second buffer layers. Then 2 x 10 18 / cm 3 A 20 nm Si-doped n-type InAs layer was grown as a contact layer. The growth rate of the InAs crystal was 1 atomic layer / second, and the arsenic molecular beam intensity was approximately 3 × 10 5 It's Torr. The method for forming the first semiconductor layer b through the contact layer was the MBE method, and the Compact21T (manufactured by Liber) was used as the apparatus.

[0042] Next, a first electrode layer 11 made of AuGe / Ni / Au was formed as a lower electrode on the bottom of the n-type GaAs (111)A substrate. After heat treatment at 420°C for 1.5 minutes, a second electrode layer 15 made of patterned Ti / Pt / Au was subsequently formed as an upper electrode on the contact layer. The first electrode layer 11 and the second electrode layer 15 were fabricated by sputtering using an ES-350SU (manufactured by Eiko). The thickness of the first electrode layer 11 was 220 nm, and the thickness of the second electrode layer 15 was 140 nm. In order to specify the size of the second semiconductor layer and evaluate its characteristics, after forming the second electrode layer 15, dry etching was performed from the contact layer to a part of the first semiconductor layer b to create a mesa structure, thereby obtaining the infrared detection element 101. Here, the mesa size was 500 × 800 μm 2 is. Thereafter, the manufactured infrared detection element 101 was mounted on a base, and wiring was formed on the first electrode layer 11 and the second electrode layer 15 to form an infrared detection device 103.

[0043] <Characteristics evaluation> For the sample before the formation of the first electrode layer 11, the region including the first and second buffer layers from the n-type GaAs(111)A substrate to the doped n-type InAs layer was observed using a cross-sectional transmission electron microscope (TEM). The results are shown in Figure 6. Here, the TEM used was an H-9500 (manufactured by Hitachi High-Technologies Corporation), and measurements were taken at an accelerating voltage of 200 kV. These results indicate that a high density of dislocations is formed at the interface, and that most of the lattice mismatch between InAs and GaAs is alleviated by the formation of a dislocation network at the interface, resulting in a low dislocation density in the InAs layer.

[0044] An optical microscope photograph of the fabricated device (infrared detector 103) is shown in Figure 7. The mesa size is 500 x 800 μm. 2 The second electrode layer 15 is made of a 0.3 × 0.3 mm 2 An opening of a size of

[0045] First, the dark current characteristics at 77 K were measured in complete darkness using the fabricated infrared detector 103. The results are shown in Figure 8. It was demonstrated that the dark current value was extremely low.

[0046] Next, the temperature characteristics of the fabricated infrared detector 103 were investigated. The results are shown in Figure 9. Here, "dark" refers to complete darkness, and the infrared radiation is emitted from a ceramic heater light source through a filter that transmits wavelengths longer than 1.5 μm. Therefore, the wavelength band of the infrared radiation is 1.5 μm or longer. As a result, it can be seen that a low dark current is maintained up to 150K (black line), and a clear signal is detected when infrared light is irradiated (gray line).

[0047] FIG. 10 shows the applied voltage dependence of the spectral sensitivity characteristics at 77K. It can be seen that the sensitivity is up to wavelengths of 2.75 μm or more, corresponding to the band gap of InAs. It can also be seen that sensitivity is present even at 0 V, and that the sensitivity becomes even higher as the voltage is increased.

[0048] Figure 11 shows the results of an evaluation of the linearity of the sensitivity characteristics with respect to the incident light intensity at 77 K. A 1.55 μm laser was used as the infrared light source. As a result, it was confirmed that the fabricated infrared detector 103 has good characteristics, in that linearity with respect to the incident light intensity is maintained even when the applied voltage is changed.

[0049] Example 3 In Example 3, we investigated the effect of increasing the thickness of the undoped GaAs layer, which is the first buffer layer, from 10 nm in Example 1 to 40 nm. As shown in Fig. 12, the infrared detector 104 conforms to Example 1 except for the thickness of the first buffer layer.

[0050] 13, by thickening the undoped GaAs layer serving as the first buffer layer, the number of electrons injected from the n-GaAs layer serving as the second semiconductor layer 14 is reduced, and dark current is suppressed up to a relatively high temperature of 200 K. Also, it can be seen that while the infrared detection sensitivity is lower than that of Example 1 using a thin film in the low temperature range of 150 K or less, good sensitivity is achieved even at 200 K.

[0051] Example 3 In Example 3, the undoped GaAs layer serving as the first buffer layer was thickened from 10 nm in Example 1 to 20 nm so that infrared detection was possible even at room temperature, and the n-InAs layer serving as the second semiconductor layer 14 was also thickened from 300 nm to 500 nm to investigate the effects thereof. Here, as shown in Fig. 14, the infrared detection device 105 conforms to Example 1 except for the thickness of the first buffer layer.

[0052] The spectral sensitivity characteristics of the infrared detector 105 at room temperature (298K) are shown in FIG. These results show that infrared detection is possible up to wavelengths exceeding 3000 nm even at room temperature. [Industrial Applicability]

[0053] As described above, the present invention provides an infrared detection device that is inexpensive, has low dark current, and is highly sensitive. Infrared detection devices are widely used in both consumer and industrial applications, such as gas sensors, motion sensors, heat source monitoring sensors, and night vision cameras. For this reason, it is believed that the infrared detection device of the present invention will greatly contribute to the development of industry. [Explanation of symbols]

[0054] 11: First electrode layer 12: First semiconductor layer, GaAs 13:Buffer layer 14: Second semiconductor layer, InAs 15: Second electrode layer 21:Ammeter 22: DC power supply, voltage source 23: Wiring 101: Infrared detector 102: Infrared detector 103: Infrared detector 104: Infrared detector 105: Infrared detector

Claims

1. a first electrode layer, a first semiconductor layer, a first buffer layer, a second buffer layer, a second semiconductor layer, and a second electrode layer are sequentially stacked; the band gap of the first semiconductor layer is wider than the band gap of the second semiconductor layer; the first buffer layer is an undoped layer made of the same material as the first semiconductor layer, the second buffer layer is an undoped layer made of the same material as the second semiconductor layer, the first semiconductor layer and the second semiconductor layer have the same conductivity type; The infrared detection element, wherein the second semiconductor layer contains InX (X is an element of Group 5).

2. 2. The infrared detection element according to claim 1, wherein said first semiconductor layer is made of GaAs or Si.

3. 3. The infrared detector according to claim 2, wherein said first semiconductor layer is GaAs(111).

4. 3. The infrared detector according to claim 2, wherein said first semiconductor layer is GaAs(100).

5. 5. The infrared detection element according to claim 1, wherein said X is at least one selected from the group consisting of As and Sb.

6. 6. The infrared detection element according to claim 1, wherein the first semiconductor layer and the second semiconductor layer contain a dopant.

7. 7. The infrared detection element according to claim 6, wherein the dopant of said first semiconductor layer is one or more selected from the group consisting of Si, S, As and P when said first semiconductor layer is of n-type.

8. 7. The infrared detection element according to claim 6, wherein the dopant of said first semiconductor layer is one or more selected from the group consisting of Zn, Be, C, B and Al when said first semiconductor layer is p-type.

9. 8. The infrared detection element according to claim 7, wherein the dopant of said second semiconductor layer is one or more selected from the group consisting of Si, S, Te and C when said first semiconductor layer is of n-type.

10. 9. The infrared detection element according to claim 8, wherein the dopant of said second semiconductor layer is one or more selected from the group consisting of Zn, Be, C, and Ge when said first semiconductor layer is p-type.

11. The amount of dopant in the first semiconductor layer and the second semiconductor layer is 2×10 １６ / cm ３ 1x10 or more １９ / cm ３ 11. The infrared detection element according to claim 6, wherein:

12. 12. The infrared detection element according to claim 1, wherein the second semiconductor layer has a thickness of 50 nm to 10 [mu]m.

13. 13. The infrared detection element according to claim 1, wherein the total thickness of the first and second buffer layers is 0.2 nm to 50 nm.

14. 14. The infrared detection element according to claim 1, wherein the first electrode layer and the second electrode layer are made of one or more metals selected from the group consisting of Al, Ti, W, Pt, Au, Ag, Cu, Ru, Rh, Pd, Ni, Sn, Zn, Ge, and In, an alloy containing the metal, a compound containing the metal, poly-Si, or graphite.

15. Providing a first semiconductor layer; forming a first buffer layer on a first main surface of the first semiconductor layer by MBE or MOCVD; forming a second buffer layer on the first main surface of the first buffer layer by MBE or MOCVD; forming a second semiconductor layer on the second buffer layer by MBE or MOCVD; forming an electrode layer on at least a portion of a second main surface of the first electrode layer; forming a second electrode layer on at least a portion of the second semiconductor layer; the band gap of the first semiconductor layer is wider than the band gap of the second semiconductor layer; the first semiconductor layer and the second semiconductor layer have the same conductivity type; the first buffer layer is an undoped layer made of the same material as the first semiconductor layer, the second buffer layer is an undoped layer made of the same material as the second semiconductor layer, The method for manufacturing an infrared detection element, wherein the second semiconductor layer contains InX (X is an element of Group 5).

16. 15. An infrared detection device comprising the infrared detection element according to claim 1, and a circuit in which a DC power supply and an ammeter are electrically connected in series between the first electrode layer and the second electrode layer.

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