JP2018200915A - Compound semiconductor device, infrared detector, and imaging device - Google Patents

Abstract

To provide a compound semiconductor device capable of improving the sensitivity of a pixel, an infrared detector, and an imaging device.SOLUTION: A compound semiconductor device 100 includes a substrate 101 and a plurality of pixels 1 two-dimensionally arranged on the surface of the substrate 101. The substrate 101 includes a photonic region 10 exhibiting a photonic effect on the light irradiated to the substrate 101.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a compound semiconductor device, an infrared detector, and an imaging device.

  The infrared imaging device includes an infrared detection element (light receiving element), a read out integrated circuit (ROIC), an optical system, and the like. The light receiving element is provided with a pixel array in which pixels that generate an electrical signal corresponding to the amount of incident infrared rays are two-dimensionally arranged. For example, a quantum well infrared sensor (Quantum Well Infrared Photodetector: QWIP) A quantum dot infrared sensor (Quantum Dot Infrared Photodetector: QDIP) is used. QWIP and QDIP have advantages in that they can be manufactured at a high yield and are advantageous for increasing the number of pixels, compared to bulk type light receiving elements.

  However, QWIP and QDIP have a problem that it is difficult to improve sensitivity as compared with a bulk type light receiving element.

Japanese Patent Laid-Open No. 2-241064 JP-A-5-315578 JP 2000-164918 A JP 2007-73571 A

  An object of the present invention is to provide a compound semiconductor device, an infrared detector, and an imaging device that can improve the sensitivity of a pixel.

  One embodiment of the compound semiconductor device includes a substrate and a plurality of pixels arranged two-dimensionally on the surface of the substrate. The substrate includes a photonic region that exhibits a photonic effect with respect to light irradiated on the substrate.

  One aspect of the infrared detector includes the above-described compound semiconductor device and a readout integrated circuit connected to the compound semiconductor device.

  One aspect of the imaging device includes the above-described infrared detector.

  In one embodiment of a method for manufacturing a compound semiconductor device, a plurality of pixels arranged two-dimensionally are formed on a surface of a substrate, and a photonic region that exhibits a photonic effect on light irradiated on the substrate is formed on the substrate To do.

  According to the above-described compound semiconductor device or the like, the appropriate photonic region is included in the substrate, so that the sensitivity of the pixel can be improved.

It is a figure which shows the structure of the infrared detector provided with the compound semiconductor device which concerns on 1st Embodiment. It is sectional drawing which shows the structure of an active layer. It is a figure which shows the structure of the photonic area | region in 1st Embodiment. It is a figure which shows the effect | action of a compound semiconductor device. It is sectional drawing which shows the manufacturing method of the compound semiconductor device which concerns on 1st Embodiment to process order. FIG. 5B is a cross-sectional view illustrating the method of manufacturing the compound semiconductor device in the order of steps, following FIG. 5A. It is sectional drawing which shows the method of forming a photonic area | region in order of a process. It is a figure which shows the structure of the photonic area | region in 2nd Embodiment. It is a figure which shows the structure of the photonic area | region in 3rd Embodiment. It is sectional drawing which shows the modification of 1st Embodiment. It is a figure which shows the imaging device which concerns on 4th Embodiment.

  The inventor of the present application has intensively studied to solve the above problems. As a result, the conventional light receiving elements using QWIP and QDIP use an antireflection film to increase the amount of incident light. However, the conventional antireflection film has a moderate wavelength dependence and is It became clear that it was not possible to capture only infrared rays of the wavelength. In addition, a reflection structure is provided in the light receiving element in order to increase the absorption efficiency of infrared light taken into the light receiving element, but it is also clear that the ratio of infrared light emitted from the light receiving element without being absorbed by QWIP or QDIP is high. Became. Furthermore, it has been found that these problems can be solved by providing a photonic region on the substrate.

  Hereinafter, embodiments will be described in detail with reference to the accompanying drawings.

(First embodiment)
First, the first embodiment will be described. The first embodiment relates to a compound semiconductor device used as a back-illuminated infrared detection element. FIG. 1 is a diagram illustrating a configuration of an infrared detector including the compound semiconductor device according to the first embodiment. FIG. 1A shows an overall image of an infrared detector, and FIG. 1B shows a configuration of a pixel.

  As shown in FIG. 1A, the infrared detector 300 includes a compound semiconductor device 100 and a readout integrated circuit (ROIC) 200 according to the first embodiment. The compound semiconductor device 100 includes a substrate 101 and a plurality of pixels (light receiving cells) 1. The pixels 1 are two-dimensionally arranged on the surface of the substrate 101. The ROIC 200 includes, for example, an element such as a silicon substrate and a transistor formed on the surface of the silicon substrate. The electrodes of the compound semiconductor device 100 are connected to the ROIC 200 via bumps. As the bump, for example, an indium or indium alloy bump is used. Copper or copper alloy bumps may be used.

As shown in FIG. 1B, a contact layer 102, an active layer 103, a contact layer 104, and a reflective layer 105 are formed on a substrate 101. A groove 109 is formed in the active layer 103, the contact layer 104, and the reflective layer 105 as an element isolation region that defines the pixel 1. The substrate 101 includes a photonic region 10 that exhibits a photonic effect on light irradiated on the substrate 101. The substrate 101 is, for example, a GaAs substrate having a surface mirror index of (100). The contact layers 102 and 104 are, for example, n-type GaAs layers having a thickness of 200 nm to 300 nm and an electron concentration of 0.5 × 10 ¹⁸ cm ^{−3 to} 1.5 × 10 ¹⁸ cm ⁻³ . The contact layers 102 and 104 are doped with, for example, Si. FIG. 2 is a cross-sectional view showing the configuration of the active layer. As shown in FIG. 2, the active layer 103 has, for example, a superlattice structure in which a GaAs barrier layer 111 and an InAs quantum dot layer 112 are repeatedly stacked about 10 to 20 times. For example, the density of InAs quantum dots included in the quantum dot layer 112 is 4.5 × 10 ¹⁰ cm ^{−2 to} 5.5 × 10 ¹⁰ cm ⁻² , the diameter is 15 nm to 25 nm, and the height is 3 nm to 7 nm. The reflective layer 105 includes, for example, a Ti film and an Au film thereon. For example, a GaAs layer having a thickness of 50 nm to 150 nm may be included as a buffer layer between the substrate 101 and the contact layer 102.

  FIG. 3 is a diagram illustrating a configuration of the photonic region in the first embodiment. As shown in FIG. 3, in the photonic region 10, a plurality of cylindrical holes 11 are periodically formed in the substrate 101. The hole 11 extends in a direction inclined from the thickness direction of the substrate 101. The angle θ between the direction in which the hole 11 extends, that is, the main axis of the hole 11 and the thickness direction of the substrate 101 is, for example, 45 ° to 60 °. In order to obtain an excellent photonic effect, the period f of the hole 11 is preferably 0.20 to 0.30 times the optical distance of the wavelength of light to be detected, and is 0.25 times (1/4 times). Is particularly preferred. Here, the period f of the holes 11 refers to the period of the plurality of holes 11 overlapping in plan view. For example, when the substrate 101 is a GaAs substrate, the wavelength of light to be detected is 10 μm, and the angle θ between the direction in which the hole 11 extends and the thickness direction of the substrate 101 is 45 °, the GaAs Since the refractive index is 3.3, the period f of the holes 11 is preferably (10 / 3.3) × 0.25 / 1.41 = 0.54 μm.

  An electrode 106 is formed on the contact layer 102, and an electrode 107 is formed on the reflective layer 105. The electrode 106 and the electrode 107 include, for example, an AuGe film and an Au film thereon.

  Next, the operation of the compound semiconductor device 100 will be described. FIG. 4 is a diagram illustrating the operation of the compound semiconductor device 100. In the compound semiconductor device 100, as shown in FIG. 4, the back surface 101a of the substrate 101 is irradiated with infrared rays. The infrared IR1 irradiated on the back surface of the substrate 101 includes various wavelength components as shown in FIG. 4B. As shown in FIG. 4C, the resonance conditions of the photonic region 10 are changed. Only infrared rays having a specific wavelength component to be filled are transmitted through the photonic region 10. That is, the photonic region 10 functions as a wavelength selection filter, and only the infrared ray IR2 having a specific wavelength that satisfies the resonance condition reaches the active layer 103. The active layer 103 absorbs infrared rays IR2 and generates charges. Part of the infrared IR2 is not absorbed by the active layer 103, reaches the reflective layer 105, and is reflected by the reflective layer 105. Part of the infrared IR2 reflected by the reflective layer 105 is absorbed by the active layer 103, and part of it reaches the photonic region 10. Since the surface of the reflective layer 105 on the active layer 103 side is not completely flat, the infrared IR2 reflected by the reflective layer 105 is often a little from the normal direction of the surface of the photonic region 10 on the active layer 103 side. Inclined. In addition, the photonic region 10 has a transmission characteristic having a strong angle dependency and transmits the infrared ray IR2 that is incident from the normal direction of the surface on the active layer 103 side, but is incident from a direction inclined from the normal direction. Infrared IR2 is reflected. For this reason, most of the infrared rays IR2 that have reached the photonic region 10 cannot be transmitted through the photonic region 10, but are reflected. Therefore, in the compound semiconductor device 100, the infrared IR2 is easily confined by the reflective layer 105 and the photonic region 10, and the amount of infrared IR2 absorbed by the active layer 103 is significantly improved.

  The electric charges generated in the active layer 103 are output as current to the ROIC 200 through bumps connected to the electrodes 106 and 107, and the output voltage corresponding to the current flowing between the electrodes 106 and 107 is measured by the ROIC 200.

  According to such a compound semiconductor device 100 according to the first embodiment, the wavelength selectivity of infrared rays reaching the active layer 103 is excellent, and the amount of infrared rays absorbed by the active layer 103 is large, so that infrared rays are detected with high sensitivity. can do.

  Next, a method for manufacturing the compound semiconductor device 100 according to the first embodiment will be described. 5A to 5B are cross-sectional views illustrating the method of manufacturing the compound semiconductor device 100 according to the first embodiment in the order of steps.

  First, as shown in FIG. 5A (a), a contact layer 102, an active layer 103, a contact layer 104, and a reflective layer 105 are formed on a substrate 101. The contact layer 102, the active layer 103, and the contact layer 104 can be formed by a crystal growth method such as a molecular beam epitaxy (MBE) method, for example. The reflective layer 105 can be formed by, for example, a vapor deposition method.

  Next, as shown in FIG. 5A (b), a trench 109 is formed as an element isolation region that defines the pixel 1. The groove 109 is formed so as to reach the contact layer 102.

  Thereafter, as shown in FIG. 5B (c), an electrode 106 is formed on the contact layer 102, and an electrode 107 is formed on the reflective layer 105. The electrodes 106 and 107 can be formed by vapor deposition, for example.

  Subsequently, as shown in FIG. 5B (d), the photonic region 10 is formed on the substrate 101. FIG. 6 is a cross-sectional view showing a method of forming a photonic region in the order of steps.

  First, as shown in FIG. 6A, a Si-containing resist 151 is formed on the back surface of the substrate 101. Next, as shown in FIG. 6B, circular openings 152 are formed in the Si-containing resist 151 at regular intervals using an electron beam exposure apparatus. Thereafter, the substrate 101 is etched using an anisotropic plasma etching apparatus. At this time, the substrate 101 is inclined with respect to the etching direction. As a result, as shown in FIG. 6C, a cylindrical hole 11 whose main axis is inclined from the thickness direction of the substrate 101 is formed.

  In this way, the compound semiconductor device 100 can be manufactured.

  For example, in the compound semiconductor device 100 in which the angle θ between the main axis of the hole 11 and the thickness direction of the substrate 101 is 45 ° and the thickness of the photonic region 10 is 1 μm, the photonic region 10 is not included. The S / N ratio is improved by about 50% as compared with the reference example in which the antireflection film is provided on the back surface of the substrate.

(Second Embodiment)
Next, a second embodiment will be described. The second embodiment is different from the first embodiment in the configuration of the photonic region. FIG. 7 is a diagram illustrating a configuration of a photonic region in the second embodiment.

  The substrate 101 of the compound semiconductor device according to the second embodiment includes a photonic region 20 including three sub-regions 20a, 20b, and 20c arranged in the thickness direction of the substrate 101, instead of the photonic region 10. It is. In the sub-region 20a, a plurality of cylindrical holes 21a are periodically formed in the GaAs film. The hole 21 a extends in a direction inclined from the thickness direction of the substrate 101. The angle θa formed by the direction in which the hole 21a extends, that is, the main axis of the hole 21a and the thickness direction of the substrate 101 is, for example, 45 ° to 60 °. In the sub-region 20b, a plurality of cylindrical holes 21b are periodically formed in the GaAs film. The hole 21 b extends in a direction inclined from the thickness direction of the substrate 101. The angle θb between the direction in which the hole 21b extends, that is, the main axis of the hole 21b and the thickness direction of the substrate 101 is, for example, 45 ° to 60 °. In the sub-region 20c, a plurality of cylindrical holes 21c are periodically formed in the GaAs film. The hole 21 c extends in a direction inclined from the thickness direction of the substrate 101. A direction θc between the direction in which the hole 21c extends, that is, the angle between the main axis of the hole 21c and the thickness direction of the substrate 101 is, for example, 45 ° to 60 °. In plan view, the direction in which the hole 21a extends is parallel to the direction in which the hole 21c extends, and the direction in which the hole 21b extends is orthogonal to these. As in the first embodiment, in order to obtain an excellent photonic effect, the period of the hole 21a, the period of the hole 21b, and the period of the hole 21c are 0.20 to 0 of the optical distance of the wavelength of the light to be detected. .30 times is preferable, and 0.25 times (1/4 times) is particularly preferable. Other configurations are the same as those of the first embodiment.

  The photonic region 20 of the second embodiment exhibits better selectivity of infrared rays to be transmitted and reflectivity to infrared rays transmitted through the active layer 103 than the photonic region 10. Therefore, the compound semiconductor device according to the second embodiment can detect infrared rays with higher sensitivity.

  The photonic region 20 can be formed as follows, for example. Similar to the first embodiment, the sub-region 20a is formed by forming the hole 21a in the GaAs substrate. Separately, the sub-region 20b is prepared by forming the hole 21b in the GaAs film, and the sub-region 20c is prepared by forming the hole 21c in the other GaAs film. Then, a sub-region 20b is provided on the sub-region 20a, and a sub-region 20c is provided on the sub-region 20b. In this way, a substrate including the photonic region 20 is obtained.

(Third embodiment)
Next, a third embodiment will be described. The third embodiment is different from the first embodiment in the configuration of the photonic region. FIG. 8 is a diagram illustrating a configuration of a photonic region in the third embodiment.

  The substrate 101 of the compound semiconductor device according to the third embodiment includes a photonic region 30 instead of the photonic region 10. In the photonic region 30, a plurality of cylindrical holes 31a and holes 31b are periodically formed in the GaAs film. The holes 31 a and 31 b extend in a direction inclined from the thickness direction of the substrate 101. The angle θa between the direction in which the hole 31a extends, that is, the main axis of the hole 31a and the thickness direction of the substrate 101 is, for example, 45 ° to 60 °, and the direction in which the hole 31b extends, ie, the main axis of the hole 31b and the substrate. An angle θb formed by the thickness direction of 101 is 45 ° to 60 °, for example. In a plan view, the direction in which the hole 31a extends and the direction in which the hole 31c extends are orthogonal to each other. As in the first embodiment, in order to obtain an excellent photonic effect, the period of the hole 31a, the period of the hole 31b, and the period of the hole 21c are 0.20 to 0 of the optical distance of the wavelength of the light to be detected. .30 times is preferable, and 0.25 times (1/4 times) is particularly preferable. Other configurations are the same as those of the first embodiment.

  The photonic region 30 of the third embodiment exhibits better selectivity of infrared rays to be transmitted and reflectivity to infrared rays transmitted through the active layer 103 than the photonic region 10. Therefore, the compound semiconductor device according to the third embodiment can detect infrared rays with higher sensitivity.

  The photonic region 30 can be obtained, for example, by forming the hole 31b before or after forming the hole 31a in the GaAs substrate.

  In the second embodiment and the third embodiment, the active layer 103 is configured so that two or three specific wavelengths can be detected, and the period is set between the holes 21a to 21c so as to correspond to these specific wavelengths. You may make it differ, and you may make a period differ between holes 31a-31b. In this case, multi-wavelength infrared can be detected.

  As shown in FIG. 9, it is preferable that an optical component 108, for example, a diffraction grating, which changes the traveling direction of light is provided between the active layer 103 and the reflective layer 105. This is because the light reflected by the reflective layer 105 and not completely absorbed by the active layer 103 does not easily pass through the photonic region. The second and third embodiments also preferably include an optical component 108 such as a diffraction grating.

  If the number of holes per unit area of the substrate surface is constant, the larger the angle formed between the main axis of the photonic region holes and the thickness direction of the substrate, the more the number of holes per unit thickness of the photonic region. Many. Therefore, when the thickness of the photonic region and the optical distance are constant, the larger the angle formed between the main axis of the hole and the thickness direction of the substrate, the smaller the number of holes. In this respect, the angle formed between the main axis of the hole and the thickness direction of the substrate is preferably 45 ° or more. On the other hand, if the angle between the main axis of the hole and the thickness direction of the substrate is too large, it may be difficult to form the hole. In this respect, the angle formed between the main axis of the hole and the thickness direction of the substrate is preferably 60 ° or less. Note that the photonic region may occupy a part of the substrate or the entire substrate. The hole period is preferably 10 μm or less, and more preferably 5 μm or less, although it depends on the specific wavelength and angle of the detection target.

  Examples of the substrate include an InP substrate, an InSb substrate, a GaSb substrate, a CdTe substrate, and a CdZnTe substrate in addition to a GaAs substrate.

(Fourth embodiment)
Next, a fourth embodiment will be described. The fourth embodiment relates to an imaging apparatus including a light receiving element. FIG. 10 is a diagram illustrating an imaging apparatus according to the fourth embodiment.

  As illustrated in FIG. 10, the imaging apparatus 400 according to the fourth embodiment includes a substantially cylindrical container 413, and a cooling head 411 is disposed in the container 413. An infrared detector 403 including a light receiving element 401 and a ROIC 402 is mounted on the cooling head 411. Any of the compound semiconductor devices of the first to third embodiments is used for the light receiving element 401, and the electrodes of the light receiving element 401 are connected to the ROIC 402 through bumps. The cooling head 411 is thermally connected to a cooling device such as a refrigerator or a Peltier element via a cold finger 412 and is cooled by the cooling device. An infrared transmission window 414 is provided at the end of the container 413, and infrared light enters the container 413 through the infrared transmission window 414 and is received by the light receiving element 401. The surface of the cooling head 411 on which the infrared detector 403 is mounted is covered with a cold shield 415. The imaging device 400 is used by being arranged behind the lens 421. As the bump, for example, an indium or indium alloy bump is used. Copper or copper alloy bumps may be used.

  In the present embodiment, infrared rays that have passed through the lens 421 and the infrared transmission window 414 and entered the light receiving element 401 are sufficiently absorbed by the active layer 103 of the light receiving element 401. Therefore, a clear infrared image with high sensitivity can be obtained.

  Hereinafter, various aspects of the present invention will be collectively described as supplementary notes.

(Appendix 1)
A substrate,
A plurality of pixels arranged two-dimensionally on the surface of the substrate;
Have
The compound semiconductor device, wherein the substrate has a photonic region exhibiting a photonic effect with respect to light irradiated on the substrate.

(Appendix 2)
The photonic region has a plurality of holes extending in a direction inclined from the thickness direction of the substrate,
The compound semiconductor device according to appendix 1, wherein the holes are periodically arranged.

(Appendix 3)
The compound semiconductor device according to appendix 2, wherein a direction in which the hole extends is 2 or more.

(Appendix 4)
4. The compound semiconductor device according to appendix 2 or 3, wherein an angle between the direction in which the hole extends and the thickness direction of the substrate is 45 ° or more.

(Appendix 5)
The pixel is
An active layer that absorbs light and generates charge in response to the absorbed light;
A reflective layer that reflects light transmitted through the active layer toward the active layer;
5. The compound semiconductor device according to any one of appendices 1 to 4, wherein:

(Appendix 6)
6. The compound semiconductor device according to appendix 5, wherein the pixel includes an optical component that is provided between the active layer and the reflective layer and changes a traveling direction of light transmitted through the active layer.

(Appendix 7)
7. The compound semiconductor device according to any one of appendices 1 to 6, wherein the substrate is a GaAs substrate, InP substrate, InSb substrate, GaSb substrate, CdTe substrate, or CdZnTe substrate.

(Appendix 8)
The compound semiconductor device according to any one of appendices 1 to 7,
A readout integrated circuit connected to the compound semiconductor device;
An infrared detector characterized by comprising:

(Appendix 9)
An imaging apparatus comprising the infrared detector according to appendix 8.

(Appendix 10)
Forming a plurality of pixels arranged two-dimensionally on the surface of the substrate;
Forming a photonic region that exhibits a photonic effect on the light applied to the substrate on the substrate;
A method for producing a compound semiconductor device, comprising:

1: Pixel 10, 20, 30: Photonic region 11, 21a, 21b, 21c, 31a, 31b: Hole 100: Compound semiconductor device 101: Substrate 103: Active layer 105: Reflective layer 108: Optical component 200: ROIC
300: Infrared detector 400: Imaging device 401: Light receiving element (compound semiconductor device)
402: ROIC
403: Infrared detector

Claims (8)

A substrate,
A plurality of pixels arranged two-dimensionally on the surface of the substrate;
Have
The compound semiconductor device, wherein the substrate has a photonic region exhibiting a photonic effect with respect to light irradiated on the substrate. The photonic region has a plurality of holes extending in a direction inclined from the thickness direction of the substrate,
The compound semiconductor device according to claim 1, wherein the holes are periodically arranged.   The compound semiconductor device according to claim 2, wherein a direction in which the hole extends is 2 or more. The pixel is
An active layer that absorbs light and generates charge in response to the absorbed light;
A reflective layer that reflects light transmitted through the active layer toward the active layer;
The compound semiconductor device according to claim 1, comprising:   The compound semiconductor device according to claim 4, wherein the pixel includes an optical component that is provided between the active layer and the reflective layer and changes a traveling direction of light transmitted through the active layer. A compound semiconductor device according to any one of claims 1 to 5,
A readout integrated circuit connected to the compound semiconductor device;
An infrared detector characterized by comprising:   An imaging apparatus comprising the infrared detector according to claim 6. Forming a plurality of pixels arranged two-dimensionally on the surface of the substrate;
Forming a photonic region that exhibits a photonic effect on the light applied to the substrate on the substrate;
A method for producing a compound semiconductor device, comprising:

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