JP6056249B2 - Photodetector, imaging device using the same, and method of manufacturing photodetector - Google Patents

Description

  The present invention relates to a photodetector, an imaging device using the same, and a method for manufacturing the photodetector.

  A quantum well infrared detector (QWIP) is a type of photodetector that detects light by capturing a current that flows when incident light is absorbed. In recent years, there has been an increasing demand for higher image quality of imaging elements (FPA: Focal Plane Array) using QWIP. Since the pixel area is reduced as the number of pixels is increased, improvement in sensitivity of the detector is required.

  As shown in FIG. 1, in GaAs / AlGaAs-based QWIP, AlGaAs acts as a potential barrier against carrier energy. GaAs acts as a potential well, and quantum levels are discretely formed inside the GaAs quantum well. This energy difference between the quantum levels corresponds to a detectable wavelength of light. When light is incident, carriers are excited and detected as a signal current.

  FIG. 2 is a cross-sectional view of a conventional QWIP 100. As shown in FIG. As the quantum well structure of the QWIP 100, a horizontal stack is generally used, and the barrier layer 103 and the quantum well layer 102 are formed horizontally with the surface of the substrate 106 (see, for example, Patent Document 1). A lower electrode layer 107a is formed on the substrate 106 via a buffer layer 108, and a barrier layer 102 and a quantum well layer 103 are alternately stacked on the lower electrode layer 107a to form a multiple quantum well 105. . On the multiple quantum well 105, an upper electrode layer 107b is formed, and an optical coupling structure 104 for irregularly reflecting incident infrared rays is formed on the outermost surface thereof. A voltage applying electrode 109 is formed on the upper electrode layer 107b and the lower electrode layer 107a.

  Infrared rays are incident perpendicular to the substrate. In the conventional infrared detector, the incident infrared ray has an electric field component only in the horizontal direction with respect to the quantum well, so that no infrared absorption occurs in the multiple quantum well 105. Incident infrared light passes through the substrate 106, the lower electrode layer 107a, the multiple quantum well 105, and the upper electrode layer 107b, and is irregularly reflected by the outermost optical coupling structure 104. The irregularly reflected infrared rays generate an electric field component in a direction perpendicular to the quantum well, and the reflected infrared rays are incident again on the multiple quantum well 105, so that the quantum well layer 103 absorbs the infrared rays. Carriers in the quantum well are excited and flow between the electrodes 107a and 107b as photocurrent. Infrared light can be detected by detecting this photocurrent.

  In the conventional infrared detector, infrared rays pass through the electrode layers 107a and 107b before entering the multiple quantum well 105, which is a light receiving layer. In the electrode layers 107a and 107b doped with impurities, part of infrared rays is absorbed by free carrier absorption (see, for example, Non-Patent Document 1). As a result, the intensity of infrared rays incident on the multiple quantum well 105 is reduced, and the flowing photocurrent is reduced.

JP 2008-198849 A

Physical Review, Volume 114, Number 1, pp.59-63 (1959)

  It is an object of the present invention to improve the sensitivity of a photodetector by preventing a reduction in the intensity of infrared rays incident on a multiple quantum well and increasing the photoelectric flow rate flowing with respect to the incident infrared rays as compared with the prior art.

According to one aspect of the invention, the photodetector is
A substrate not doped with impurities;
A quantum well structure including a quantum well layer and a barrier layer extending perpendicular to the substrate;
A pair of electrode layers sandwiching the quantum well structure from a direction horizontal to the substrate;
Have

  It is possible to increase the photocurrent by preventing the intensity of infrared rays incident on the multiple quantum well from being lowered, and to improve the sensitivity of the photodetector.

It is a schematic diagram which shows the excitation of the carrier in a quantum well, and generation | occurrence | production of a photocurrent. It is a figure which shows the conventional horizontal lamination type multiple quantum well structure. 1 is a schematic configuration diagram of a photodetector of Example 1. FIG. 6 is a manufacturing process diagram of the photodetector of Example 1. FIG. FIG. 5 is a manufacturing process diagram of the photodetector subsequent to the process of FIG. 4. FIG. 6 is a manufacturing process diagram of the photodetector subsequent to the process of FIG. 5. FIG. 6 is a schematic configuration diagram of a photodetector of Example 2. FIG. 10 is a manufacturing process diagram of the photodetector of Example 2. FIG. 9 is a manufacturing process diagram of the photodetector subsequent to the process of FIG. 8. FIG. 10 is a manufacturing process diagram of the photodetector subsequent to the process of FIG. 9. FIG. 11 is a manufacturing process diagram of the photodetector subsequent to the process of FIG. 10. FIG. 6 is a schematic configuration diagram of an imaging apparatus according to a third embodiment. FIG. 13 is a manufacturing process diagram of the imaging apparatus of FIG. 12. FIG. 14 is a manufacturing process diagram for an imaging device following the process in FIG. 13; FIG. 15 is a manufacturing process diagram for the imaging device, following the step in FIG. 14. FIG. 16 is a manufacturing process diagram for the imaging apparatus following the process in FIG. 15; FIG. 17 is a manufacturing process diagram for the imaging apparatus following the process in FIG. 16;

  Hereinafter, embodiments of the invention will be described with reference to the drawings. The photodetector of the embodiment and the imaging device using the same employ a vertical multiple quantum well structure in which a quantum well layer and a barrier layer are arranged perpendicular to the surface of the substrate. The electrode layer sandwiches the vertically arranged multiple quantum wells from the lateral direction, that is, from the horizontal direction to the substrate. With this configuration, light incident on the photodetector can be incident on the multiple quantum well without passing through the electrode layer doped with impurities. In addition, since it already has an electric field component in a direction perpendicular to the multiple quantum well when incident on the multiple quantum well, an optical coupling structure becomes unnecessary.

  FIG. 3 is a schematic cross-sectional view of the photodetector 10 according to the first embodiment. The photodetector 10 is an infrared detector 10 having an absorption peak with respect to infrared light having a specific wavelength.

  A lower barrier layer 22 is formed on the semiconductor substrate 16 via a buffer layer 18, and the multiple quantum well 15 is disposed on the lower barrier layer 22. In the multiple quantum well 15, the barrier layer 12 and the quantum well layer 13 are formed in a direction perpendicular to the substrate 16. The electrode layers 17a and 17b for taking out the photocurrent sandwich the multiple quantum well 15 from the lateral direction (direction parallel to the substrate 16). Ohmic electrodes 14a and 14b are formed on the electrode layers 17a and 17b, respectively. An upper barrier layer 23 is formed on the multiple quantum well 15, and a reflector 25 is formed on the outermost surface of the upper barrier layer 23. In Example 1, the reflector 25 is, for example, a metal reflective film 25 having a high reflectance.

  Infrared rays are perpendicularly incident on the substrate 16. In the configuration of FIG. 3, since the periodic pattern of the barrier layer 12 and the quantum well layer 13 is repeated in the direction horizontal to the substrate 16, the incident infrared ray has an electric field component in the direction perpendicular to the multiple quantum well 15. When an infrared ray is incident on the infrared detector 10 with a voltage applied between the electrode layers 17a and 17b, the infrared absorption occurs in the multiple quantum well 15, and the excited carriers travel and a photocurrent flows.

  The photocurrent Ip flowing through the infrared detector 10 is expressed by the formula (1).

ここで、ｅは素電荷、Φｓは入射する赤外線強度、ηは量子効率、ｇはゲインである。式（１）からわかるように、光電流は入射する赤外線の強度と比例関係にある。

Here, e is an elementary charge, Φs is an incident infrared ray intensity, η is a quantum efficiency, and g is a gain. As can be seen from equation (1), the photocurrent is proportional to the intensity of the incident infrared ray.

  In the configuration of FIG. 3, the electrode layers 17 a and 17 b doped with impurities are not located in the path until the infrared rays are incident on the multiple quantum well 15, so that absorption of infrared rays due to free carrier absorption can be prevented. The intensity of infrared light incident on the multiple quantum well 15 is higher than that of the conventional horizontal multiple quantum well, and the photocurrent is increased. Therefore, the sensitivity of the infrared detector 10 is improved.

  Further, since the infrared rays are reflected by the reflection film 25 formed on the upper barrier layer 23, the optical path length of the infrared rays passing through the multiple quantum well (light absorption layer) 15 is increased, and the sensitivity is further improved.

  The configuration of FIG. 3 is such that incident infrared light is directly incident on the multiple quantum well 15 without passing through an electrode layer, and infrared light can be detected without using an optical coupling structure. The effect is that the length can be increased.

  4 to 6 are manufacturing process diagrams of the infrared detector 10 of FIG. In the embodiment, the infrared detector 10 is manufactured by using, for example, molecular beam epitaxy (MBE).

  In FIG. 4A, the buffer layer 18 is formed on the semiconductor substrate 16. The semiconductor substrate 16 is a GaAs slightly inclined substrate, for example. The surface of the substrate 16 is inclined about 0.5 ° in the [0-11] direction, for example, from the (100) plane. Therefore, a fine step having a terrace width “w” of about 32 nm exists on the surface of the semiconductor substrate 16. The buffer layer 18 is made of, for example, intrinsic GaAs and has a thickness of about 100 nm. On the surface of the buffer layer 18, there is a step reflecting the step of the substrate 16.

In FIG. 4B, a lower barrier layer 22 of, eg, intrinsic Al _0.14 Ga _0.86 As is formed to 50 nm on the GaAs buffer layer 18. On the surface of the lower barrier layer 22, there are steps that reflect the steps of the substrate 16.

  Next, the multiple quantum well 15 is formed perpendicular to the substrate 16. The vertical multiple quantum well 15 is formed by repeatedly producing a fractional layer superlattice structure using a step flow growth mode. As a specific example, in FIG. 4C, Ga and As are supplied so that the intrinsic GaAs quantum well layer 13 grows from the end of the step by an amount corresponding to the width “w1” of 5 nm. Since the surface of the wafer has a step reflecting the step of the GaAs substrate 16, the supplied raw material sufficiently diffuses the wafer surface and is taken into the step edge. For this reason, the GaAs quantum well layer 13 is formed along the side surface of each step. The growth rate of GaAs is, for example, 0.3 μm / h, and the film formation temperature is 600 ° C.

Next, in FIG. 5A, an intrinsic AlGaAs barrier layer 12 is formed. For example, the raw material is supplied so that the genuine Al _0.14 Ga _0.86 As layer 12 is grown from the end of the GaAs quantum well layer 13 by an amount corresponding to the width “w2” of 27 nm. Similar to the quantum well layer 13, the supplied material sufficiently diffuses the wafer surface and is taken into the step edge. Therefore, a barrier layer 12 of Al _0.14 Ga _0.86 As is formed along the side surface of the quantum well layer 13.

  In FIG. 5B, using the step flow growth mode, fractional layer superlattices of GaAs and AlGaAs are repeatedly formed until the thickness of the multiple quantum well 15 reaches 2000 nm. One period of the fractional layer superlattice composed of the quantum well layer 13 and the barrier layer 12 is the same as the step width “w” existing on the surface of the GaAs substrate 16, and the multiple quantum well 15 is formed on the surface of the GaAs substrate 16. On the other hand, it is formed vertically.

Next, in FIG. 5C, for example, an upper barrier layer 23 of intrinsic Al _0.14 Ga _0.86 As is formed to 50 nm. A reflective film 25 having a high reflectance is formed on the upper barrier layer 23 by using, for example, Au. A resist mask 27 having an opening with a predetermined shape is formed on the reflective film 25.

In FIG. 6A, the reflective film 25 and a part of the AlGaAs barrier layer 23 are etched using the resist mask 27 (see FIG. 5C). After etching, for example, Si is implanted into the opening by ion implantation to form n-type electrode layers 17a and 17b having an electron concentration of 1 × 10 ¹⁸ cm ⁻³ in a direction perpendicular to the substrate 16. Thereafter, the resist mask 27 is removed.

  Next, in FIG. 6B, ohmic electrodes 14a and 14b made of, for example, AuGe / Ni / Au are formed on the n-type electrode layers 17a and 17b. Thereby, the infrared detector 10 can be obtained.

  According to the configuration of FIG. 3 and the manufacturing method of FIGS. 4 to 6, an effect can be expected as the infrared detector 10 having a sensitive peak wavelength of about 14 μm. In the conventional infrared detector 100 of FIG. 2, the infrared intensity Φ at the time when the scattered infrared light re-enters the multiple quantum well (light receiving layer) 105 can be estimated by Expression (2).

ここで、Φ_０は検出器に入射する赤外線強度、αは電極層における赤外線の吸収係数、Ｌは赤外線が電極層を透過する距離である。従来の赤外線検出器１００で、電極層１０７ａ、１０７ｂのキャリア濃度はｎ＝２×１０^１８ｃｍ^−３、αは５５０ｃｍ^−１、赤外線が透過する電極層１０７ａ、１０７ｂの厚さは約２μｍとすると、散乱された赤外線が多重量子井戸（受光層）１０５へ入射する時点での赤外線強度Φと、検出器１００に入射する赤外線強度Φ_０の比は、

Here, Φ ₀ is the intensity of infrared rays incident on the detector, α is the absorption coefficient of infrared rays in the electrode layer, and L is the distance that infrared rays pass through the electrode layer. In the conventional infrared detector 100, the carrier concentration of the electrode layers 107a and 107b is n = 2 × 10 ¹⁸ cm ⁻³ , α is 550 cm ⁻¹ , and the thickness of the electrode layers 107a and 107b that transmits infrared rays is about 2 μm. The ratio of the infrared intensity Φ when the scattered infrared light enters the multiple quantum well (light receiving layer) 105 and the infrared intensity Φ ₀ incident on the detector 100 is

となる。

It becomes.

  On the other hand, in the infrared detector 10 of the first embodiment, the intensity of incident infrared rays is not affected by free carrier absorption in the electrode layers 17a and 17b, so that the infrared intensity incident on the multiple quantum well 15 is the conventional configuration. About 10%. The photocurrent is also increased by 10%.

The present invention is not limited to the embodiments described above. The Al composition of the lower barrier layer 22 and the upper barrier layer 23 can be appropriately selected within the range of Al _x Ga _1-x As (0 <x ≦ 1). Further, when the quantum well layer 13 is formed, Si may be simultaneously supplied to form the n-type GaAs quantum well layer 13. Further, an InP substrate may be used as the semiconductor substrate 16, the quantum well layer 13 may be In _x Ga _1-x As (0 <x <1), and the barrier layer 12 may be InP. For the formation of each layer, metal-organic chemical vapor deposition (MOCVD) may be used instead of molecular beam epitaxy.

  The width (w1 + w2) of one period of the fractional layer superlattice may be 1 / n times the step width “w” of the substrate 16 (n = 1, 2,...). The degree of inclination of the semiconductor substrate 16 is not limited to 0.5 °. Further, it may be a semiconductor substrate inclined in the [0-1-1] direction when the (100) plane is used as a reference. The substrate may be inclined in the [110] direction from the (100) plane. It doesn't matter. The carriers do not have to be electrons, and holes may be used as carriers. In this case, Be or the like can be used as an impurity to be injected into the quantum well layer 13.

  FIG. 7 is a schematic cross-sectional view of the infrared detector 30 according to the second embodiment. In the second embodiment, a distributed Bragg reflector (DBR) 39 is disposed on the upper barrier layer 23 as a reflector. Also in the second embodiment, the quantum well layer 33 and the barrier layer 32 constituting the multiple quantum well 35 are formed in a direction perpendicular to the substrate 16.

  In the infrared detector 30, the lower barrier layer 22 is formed on the semiconductor substrate 16 via the buffer layer 18, and the multiple quantum well 35 is disposed on the lower barrier layer 22. In the multiple quantum well 35, the barrier layer 32 and the quantum well layer 33 are formed in a direction perpendicular to the substrate 16. Electrode layers 17a and 17b for taking out photocurrent sandwich the multiple quantum well 35 from the lateral direction (a direction parallel to the substrate 16). Ohmic electrodes 14a and 14b are formed on the electrode layers 17a and 17b, respectively. An upper barrier layer 23 is formed on the multiple quantum well 35, and a distributed Bragg reflector 39 is formed on the upper barrier layer 23.

  Infrared rays are perpendicularly incident on the substrate 16. In the configuration of FIG. 7, the sandwiching pattern of the barrier layer 32 and the quantum well layer 33 is repeated in a direction horizontal to the substrate 16, and incident infrared rays have an electric field component in a direction perpendicular to the quantum well 35. When an infrared ray is incident on the infrared detector 30 with a voltage applied between the electrode layers 17a and 17b, infrared absorption occurs in the multiple quantum well 35 without the optical coupling structure, and the excited carriers travel. As a result, photocurrent flows.

  Infrared light that has passed through the multiple quantum well 35 is reflected by the distributed Bragg reflector 39 with high reflectivity, and reenters the multiple quantum well 35. The re-incident infrared light has an electric field component perpendicular to the multiple quantum well 35, and further infrared absorption occurs in the multiple quantum well 35.

Since the absorption coefficient α of the sensitive peak wavelength in the multiple quantum well (light receiving layer) 105 of the conventional infrared detector 100 is about 1000 cm ⁻¹ , the thickness of the multiple quantum well 15 is obtained by using the distributed Bragg reflector 39. Can be halved. Further, since there is no electrode layer 17a, 17b in the path until the infrared ray enters the multiple quantum well 35, infrared absorption due to free carrier absorption does not occur in the electrode layer 17a, 17b. The infrared intensity incident on the multiple quantum well 35 increases as compared with the conventional configuration, and the photocurrent increases. As a result, the sensitivity of the infrared detector 30 is improved.

  8 to 12 are manufacturing process diagrams of the infrared detector 30 according to the second embodiment. The infrared detector 30 is manufactured using, for example, a molecular beam epitaxy (MBE) method. The processes of FIGS. 8A to 8C are the same as the processes of FIGS. 4A to 4C of the first embodiment. As the semiconductor substrate 16, for example, a GaAs slightly inclined substrate 16 is used. As shown in FIG. 8A, the surface of the substrate 16 is inclined about 0.5 ° in the [0-11] direction, for example, from the (100) plane. Therefore, a fine step having a terrace width “w” of about 32 nm exists on the surface of the semiconductor substrate 16.

  A buffer layer 18 is formed on the substrate 16. The buffer layer 18 is an intrinsic GaAs layer, for example, and has a thickness of about 100 nm. There are also steps on the surface of the buffer layer 18 that reflect the steps of the GaAs substrate 16.

In FIG. 8B, a barrier layer 22 of, eg, intrinsic Al _0.14 Ga _0.86 As is deposited on the buffer layer 18 to a thickness of 50 nm. There is a step on the surface of the barrier layer 22 that reflects the step of the semiconductor substrate.

  In FIG. 8C, a multiple quantum well structure is formed perpendicular to the substrate. The step-flow growth mode is used to form a fractional layer superlattice structure repeatedly. For example, the raw material is supplied so that the quantum well layer 33 made of intrinsic GaAs grows by an amount corresponding to the width “w1” of 5 nm from the end of the step. At this time, since the wafer surface has a step reflecting the step of the GaAs substrate 16, the supplied material is sufficiently diffused in the wafer surface and taken into the step edge. Thereby, the quantum well layer 33 made of GaAs is formed along the side surface of each step.

In FIG. 9A, for example, an intrinsic Al _0.14 Ga _0.86 As barrier layer 32 is supplied so as to grow from the step end of the GaAs quantum well layer 33 by an amount corresponding to a width “w2” of 27 nm. To do. Similar to the quantum well layer 33, the supplied material sufficiently diffuses on the substrate surface and is taken into the step edge. Therefore, a barrier layer 32 made of Al _0.14 Ga _0.86 As is formed along the side surface of the quantum well layer 33.

  In FIG. 9B, using the step flow growth mode, the formation of the fractional layer superlattice of GaAs and AlGaAs is repeated until the thickness “d” of the multiple quantum well 35 reaches 1000 nm. This thickness is about ½ of the thickness of the multiple quantum well having the conventional structure. One period (w1 + w2) of the fractional layer superlattice composed of the quantum well layer 33 and the barrier layer 32 is the same as the step width “w” existing on the surface of the GaAs substrate 16, and the quantum constituting the multiple quantum well 35. The well layer 33 and the barrier layer 32 are formed perpendicular to the surface of the GaAs substrate 16.

In FIG. 10A, the upper barrier layer 23 of, eg, intrinsic Al _0.14 Ga _0.86 As is formed to 50 nm.

  In FIG. 10B, the distributed Bragg reflector 39 is formed. When the sensitive wavelength is λ, for example, an AlAs layer having a film thickness of λ / 4 and a GaAs layer having a film thickness of λ / 4 are alternately stacked so that the optical length of one cycle is an integral multiple of λ / 2. . A resist mask 38 having a predetermined opening is formed on the distributed Bragg reflector 39.

In FIG. 11A, electrode layers 17a and 17b are formed. Using the resist mask 38, a part of the distributed Bragg reflector 39 and the upper AlGaAs barrier layer 23 is etched. Using ion implantation, for example, Si is implanted into the etched opening, and n-type electrode layers 17a and 17b having an electron concentration of 1 × 10 ¹⁸ cm ⁻³ are formed perpendicular to the substrate. Thereafter, the resist mask 38 is removed.

  In FIG. 11B, ohmic electrodes 14a and 14b made of, for example, AuGe / Ni / Au are formed on the n-type electrode layers 17a and 17b, respectively. Thereby, the infrared detector 30 can be obtained.

  The reflector formed on the upper barrier layer 23 is not limited to DBR, and may be an arbitrary reflection grating such as a blazed diffraction grating.

  In the third embodiment, an imaging apparatus using the infrared detector 10 of the first embodiment or the infrared detector 30 of the second embodiment is provided.

  FIG. 12 shows an imaging apparatus 50 using the infrared detector 30 of the second embodiment as an example. 12A is a schematic cross-sectional view of the imaging device 50, and FIG. 12B is a perspective view.

  A plurality of infrared detectors 30 are arranged in an array on the semiconductor substrate 16 via the buffer layer 18. The bump electrodes 40 formed on the ohmic electrodes 14a and 14b of each infrared detector 30 are bonded to a circuit board 51 on which a signal readout circuit is formed. That is, each infrared detector 30 is electrically connected to the signal readout circuit via the bump electrode 40. In FIG. 12A, the light incident surface is drawn on the lower side, and the circuit board 51 is drawn on the upper side. However, in mounting, as shown in FIG. 12B, imaging in which a plurality of infrared detectors 30 are arranged. The element array 45 may be flip-chip bonded to the circuit board 51 with the light incident surface facing upward.

  13 to 17 are manufacturing process diagrams of the imaging device 50. In FIG. 13A, an intrinsic GaAs buffer layer 18 is grown to 100 nm on a GaAs finely inclined substrate 16 by using, for example, molecular beam epitaxy. As described in the second embodiment, the surface of the substrate 16 is inclined by about 0.5 ° in the [0-11] direction from the (100) plane, for example, and has a fine step (not shown) having a terrace width of about 32 nm. Exists. A step (not shown) reflecting the step of the GaAs substrate 16 also exists on the surface of the buffer layer 18.

In FIG. 13B, an intrinsic Al _0.14 Ga _0.86 As barrier layer 22 is formed on the buffer layer 18 to a thickness of 50 nm. There are also steps (not shown) on the surface of the barrier layer 22 that reflect the steps of the wafer.

  In FIG. 13C, a multiple quantum well layer 46 is formed on the barrier layer 22. The quantum well layer 33 and the barrier layer 32 of the multiple quantum well layer 46 extend in a direction perpendicular to the surface of the substrate 16. As described in the second embodiment, the multi-quantum well layer 46 is formed to have a thickness of 1000 nm by repeatedly manufacturing the fractional layer superlattice structure using the step flow growth mode.

In FIG. 14A, an upper barrier layer 23 of intrinsic Al _0.14 Ga _0.86 As is grown by 50 nm.

  In FIG. 14B, a distributed Bragg reflection layer 49 is formed on the upper barrier layer 23. When the sensitive wavelength is λ, for example, AlAs layer thickness λ / 4 and GaAs layer thickness λ / 4 are alternately stacked so that the optical length of one cycle is an integral multiple of λ / 2. A resist mask 54 having a predetermined opening 57 is formed on the distributed Bragg reflection layer 49.

  In FIG. 15A, using the resist mask 54, the distributed Bragg reflection layer 49 and a part of the upper AlGaAs barrier layer 23 are etched. Next, for example, Si is implanted into the etching opening 58 by using an ion implantation method.

In FIG. 15B, an n-type electrode layer 47 having an electron concentration of 1 × 10 ¹⁸ cm ⁻³ is formed by Si implantation, and individual multiple quantum wells 35 are formed between the n-type electrode layers 47. Thereafter, the resist mask 54 is peeled off.

  In FIG. 16A, pixel separation is performed. Lattice-like separation grooves 55 are formed in the n-type electrode layer 47 by anisotropic dry etching to form pixels arranged two-dimensionally. By this pixel separation, a pair of electrode layers 17a and 17b sandwiching the multiple quantum well 35 from the side surfaces are formed.

  In FIG. 16B, AuGe / Ni / Au ohmic electrodes 14a and 14b, for example, are formed on the n-type electrode layers 17a and 17b.

  In FIG. 17, bumps 40 made of, for example, In are formed on the ohmic electrodes 14 a and 14 b and bonded to the circuit board 51. Thereby, the imaging device 50 can be obtained.

  The imaging device of Example 3 has a structure in which a quantum well layer and a barrier layer extending perpendicularly to a substrate are repeated in a horizontal direction, and the multiple quantum well is sandwiched between electrode layers from a horizontal direction (a direction parallel to the substrate). An infrared detector is used. Therefore, in each pixel, light absorption due to free carrier absorption can be prevented, and the intensity of light incident on the multiple quantum well can be kept high. As a result, the photocurrent can be increased and the sensitivity of the entire imaging apparatus can be improved. Moreover, infrared rays can be detected without using an optical coupling structure. Furthermore, when the photodetector 30 according to the second embodiment is used, the thickness of the multiple quantum well 30 can be reduced, so that a thin imaging element array 45 (see FIG. 12B) can be manufactured. it can.

For the above explanation, the following notes are presented.
(Appendix 1)
A substrate not doped with impurities;
A quantum well structure including a quantum well layer and a barrier layer extending perpendicular to the substrate;
A pair of electrode layers sandwiching the quantum well structure from a direction horizontal to the substrate;
A photodetector comprising:
(Appendix 2)
2. The photodetector according to claim 1, wherein the substrate is an inclined substrate that is inclined stepwise in a predetermined direction from a predetermined crystal plane.
(Appendix 3)
The quantum well structure is a multiple quantum well in which the quantum well layer and the barrier layer are periodically repeated in a direction horizontal to the substrate,
The photodetector according to claim 2, wherein the period of the multiple quantum well is 1 / n (n is a natural number) times the terrace width of the inclined substrate.
(Appendix 4)
The photodetector according to any one of appendices 1 to 3, wherein a reflector is disposed above the quantum well structure in a horizontal direction with respect to the substrate.
(Appendix 5)
The photodetector according to appendix 4, wherein the reflector is a distributed reflector.
(Appendix 6)
The photodetector according to any one of appendices 1 to 5, wherein the quantum well structure has an absorption peak wavelength in an infrared band.
(Appendix 7)
An image sensor array in which the photodetectors according to any one of appendices 1 to 6 are arranged in an array; a circuit board electrically connected to the image sensor array;
An imaging apparatus having
(Appendix 8)
On a substrate not doped with impurities, a multi-quantum well layer is formed in which a quantum well layer and a barrier layer extending in a direction perpendicular to the substrate are periodically repeated in a direction horizontal to the substrate,
Impurities are implanted into a predetermined portion of the multiple quantum well layer to form a pair of electrode layers adjacent to the multiple quantum well having a certain number of periods.
The manufacturing method of the photodetector characterized by including a process.
(Appendix 9)
The photodetector according to claim 8, wherein the multiple quantum well layer is formed in a direction perpendicular to the substrate by repeatedly forming a fractional layer superlattice structure using a step flow growth mode. Manufacturing method.

10, 30 Infrared detector (light detector)
16 Semiconductor substrate 18 Buffer layer 12, 32 Barrier layer 13, 33 Quantum well layer 15, 35 Multiple quantum well (quantum well structure)
17a, 17b Electrode layer 22 Lower barrier layer 23 Upper barrier layer 45 Imaging element array 50 Imaging device 51 Circuit board

Claims (7)

A substrate not doped with impurities;
A quantum well structure including a quantum well layer and a barrier layer extending perpendicular to the substrate;
A pair of electrode layers sandwiching the quantum well structure from a direction horizontal to the substrate;
A photodetector comprising:   The photodetector according to claim 1, wherein the substrate is an inclined substrate that is inclined stepwise in a certain direction from a predetermined crystal plane. The quantum well structure is a multiple quantum well in which the quantum well layer and the barrier layer are periodically repeated in a direction horizontal to the substrate,
The photodetector according to claim 2, wherein a period of the multiple quantum well is 1 / n (n is a natural number) times a terrace width of the inclined substrate. On top of the quantum well structure, a light detector according to any one of claims 1 to 3, characterized in that it is arranged horizontally reflector relative to the substrate. An image sensor array in which the photodetectors according to any one of claims 1 to 4 are arranged in an array,
A circuit board electrically connected to the imaging element array;
An imaging apparatus having On a substrate not doped with impurities, a multi-quantum well layer is formed in which a quantum well layer and a barrier layer extending in a direction perpendicular to the substrate are periodically repeated in a direction horizontal to the substrate,
Impurities are implanted into a predetermined portion of the multiple quantum well layer to form a pair of electrode layers adjacent to the multiple quantum well having a certain number of periods.
The manufacturing method of the photodetector characterized by including a process.   The optical detection according to claim 6, wherein the multiple quantum well layer is formed in a direction perpendicular to the substrate by repeatedly forming a fractional layer superlattice structure using a step flow growth mode. Manufacturing method.

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