Photodiode and photosensitive device

Abstract

To suppress a reduction in light-receiving sensitivity of infrared light.SOLUTION: A photodiode 1 is configured to include: a p+ type semiconductor layer 13 with a first surface 13a in contact with a first electrode 11 and a surface protection film 12 located at a peripheral edge part of the first electrode 11; an n type semiconductor layer 14 in contact with a second surface 13b of the p+ type semiconductor layer 13 that is opposed to the first surface 13a; an n+ type semiconductor layer 15 in contact with a third surface 14b of the n type semiconductor layer 14 that is opposed to the surface in contact with the second surface 13b; and a second electrode 16 in contact with a fourth surface 15b of the n+ type semiconductor layer 15 that is opposed to the surface in contact with the third surface 14b. The p+ type semiconductor layer 13, the n type semiconductor layer 14, and the n+ type semiconductor layer 15 contain Mg2Si. The fourth surface 15b of the n+ type semiconductor layer 15 has a portion not in contact with the second electrode 16.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to photodiodes and light sensitive devices. [Background technology]

[0002] Patent Document 1 discloses a PN junction photodiode that uses Mg2Si. The PN junction photodiode is formed by depositing and heat-treating Mg2Si with Ag as a dopant impurity, thereby forming a local p-type layer deep in the direction of infrared light incidence. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2019 / 187222 Summary of the Invention [Problem to be solved by the invention]

[0004] In a PN junction photodiode such as the technology described in Patent Document 1, Ag is used as a dopant impurity, which can cause infrared light to be absorbed before it reaches the PN junction, resulting in a decrease in light-receiving sensitivity. [Means for solving the problem]

[0005] A photodiode according to one embodiment includes a p+ type semiconductor layer having a first surface in contact with a first electrode and a surface protective film located on the periphery of the first electrode, an n-type semiconductor layer in contact with a second surface of the p+ type semiconductor layer opposite the first surface, an n+ type semiconductor layer in contact with a third surface of the n-type semiconductor layer opposite the surface in contact with the second surface, and a second electrode in contact with a fourth surface of the n+ type semiconductor layer opposite the surface in contact with the third surface, wherein the p+ type semiconductor layer, the n-type semiconductor layer, and the n+ type semiconductor layer contain Mg2Si, and the fourth surface of the n+ type semiconductor layer has a portion that does not contact the second electrode.

[0006] One aspect of the photosensitive device includes the above-mentioned photodiode.

Advantages of the Invention

[0007] According to one aspect of the present disclosure, it is possible to suppress a reduction in the light reception sensitivity to infrared light.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0009] The photodiode and the photosensitive device according to the embodiment will be described below.

[0010] [First Embodiment] (Photodiode) FIG. 1 is a schematic cross-sectional view for explaining a photodiode according to the first embodiment. In FIG. 1, the lower side is the anode and the upper side is the cathode. The photodiode 1 is a PIN photodiode. The photodiode 1 does not require an epitaxial layer and has a Mg2Si single crystal as a substrate. The photodiode 1 irradiates infrared light IR from the cathode side and reflects it.

[0011] The infrared light IR has a wavelength of 0.8 μm or more and 3.0 μm or less.

[0012] As shown in FIG. 1, the photodiode 1 according to the embodiment includes a first electrode 11, a surface protection film 12, a p+-type semiconductor layer 13, an n-type semiconductor layer 14, an n+-type semiconductor layer 15, and a second electrode 16.

[0013] The first electrode 11 is disposed on the anode side of the photodiode 1. The first electrode 11 contains, for example, NiAu. The first electrode 11 is disposed at the central portion of the photodiode 1. The first electrode 11 is disposed inside the surface protection film 12. The first electrode 11 has a thickness of about 0.5 μm, for example. The surface of the first electrode 11 that contacts the first surface 13a of the p+-type semiconductor layer 13 is the infrared light IR reflection surface 11b.

[0014] The surface protection film 12 is a protective layer that protects the surface of the photodiode 1. The surface protection film 12 contains, for example, SiO2 or MgO. The surface protection film 12 is disposed at the peripheral portion of the first electrode 11. The surface protection film 12 has a thickness of, for example, 0.1 μm or more and 10 μm or less.

[0015] The p+-type semiconductor layer 13 is a p+-type semiconductor layer. The p+-type semiconductor layer 13 contains Mg2Si. The p+-type semiconductor layer 13 is doped with Ag. The p+-type semiconductor layer 13 has a thickness of, for example, 1 μm or more and 100 μm or less. The p+-type semiconductor layer 13 has a first surface 13a facing the anode side and a second surface 13b facing the first surface 13a. The second surface 13b faces the cathode side.

[0016] The n-type semiconductor layer 14 is in contact with the second surface 13b of the p+-type semiconductor layer 13. The n-type semiconductor layer 14 is an I layer. The n-type semiconductor layer 14 is an n-type semiconductor layer. The n-type semiconductor layer 14 contains Mg2Si. The n-type semiconductor layer 14 has a thickness of, for example, 1 μm or more and 1000 μm or less. Also, the n-type semiconductor layer 14 may have a thickness of, for example, 1 μm or more and 100 μm or less. The n-type semiconductor layer 14 has a third surface 14b facing the surface in contact with the second surface 13b of the p+-type semiconductor layer 13. The third surface 14b faces the cathode side.

[0017] The n+-type semiconductor layer 15 is in contact with the third surface 14b of the n-type semiconductor layer 14. The n+-type semiconductor layer 15 is an n+-type semiconductor layer. The n+-type semiconductor layer 15 contains Mg2Si. The n+-type semiconductor layer 15 is doped with, for example, Al, boron (B), or phosphorus (P). The n+-type semiconductor layer 15 has a thickness of, for example, 0.1 μm or more and 10 μm or less. The thinner the thickness of the n+-type semiconductor layer 15, the more preferable. The n+-type semiconductor layer 15 has a fourth surface 15b facing the surface in contact with the third surface 14b of the n-type semiconductor layer 14. The fourth surface 15b is an incident surface on which infrared light IR is incident. The fourth surface 15b has a portion that does not contact the second electrode 16.

[0018] The second electrode 16 is in contact with the fourth surface 15b of the n+-type semiconductor layer 15. The second electrode 16 is disposed on the cathode side of the photodiode 1. The second electrode 16 contains, for example, Cr, Ti, or Au. The second electrode 16 is disposed, for example, annularly at the peripheral portion of the photodiode 1. The second electrode 16 has a thickness of, for example, about 0.5 μm.

[0019] In the photodiode 1 configured as described above, infrared light IR is incident from the n-type layer opposite to the p-type layer. Infrared light IR is incident on the back surface of the photodiode 1.

[0020] (Photosensitive device) By arranging the photodiodes 1 configured as described above in an array, they can be used as photosensitive devices such as, for example, photodetectors and imaging devices.

[0021] (Function) The reflection of infrared light IR in the photodiode 1 will be described. Infrared light IR is incident from the fourth surface 15b of the n+-type semiconductor layer 15. Infrared light IR is incident from the cathode side, in other words, from the back surface. The infrared light IR incident from the fourth surface 15b passes through the n+-type semiconductor layer 15, the n-type semiconductor layer 14, and the p+-type semiconductor layer 13, and is reflected by the reflection surface 11b of the first electrode 11. The return light of the infrared light IR reflected by the reflection surface 11b of the first electrode 11 returns to the n-type semiconductor layer 14 side.

[0022] Since the photodiode 1 is a PIN photodiode, the n-type semiconductor layer 14, which is the I layer, is depleted. Also, since the infrared light IR is incident from the back surface, it reaches the n-type semiconductor layer 14, which is the I layer, without passing through the p+-type semiconductor layer 13. As a result, the infrared light IR reaches the n-type semiconductor layer 14 without being significantly absorbed. Moreover, the light reception sensitivity is further improved by the return light of the infrared light IR reflected by the reflecting surface 11b of the first electrode 11.

[0023] (Effect) In the present embodiment, since it is a PIN photodiode, the n-type semiconductor layer 14, which is the I layer, can be depleted. In the present embodiment, since the infrared light IR is incident from the back surface, the infrared light IR can reach the n-type semiconductor layer 14, which is the I layer, without being significantly absorbed. In the present embodiment, the light reception sensitivity can be further improved by the return light of the infrared light IR reflected by the reflecting surface 11b of the first electrode 11.

[0024] On the other hand, conventionally, when the infrared light IR is incident from the front surface, it is absorbed in the p+-type semiconductor layer 13 doped with Ag before reaching the PN junction. As a result, the light reception sensitivity is lowered.

[0025] In the present embodiment, when it is necessary to reduce the thickness in order to deplete the entire n-type semiconductor layer 14, which is the I layer, absorption can be promoted by the reflected light of the infrared light IR while keeping the thickness reduced.

[0026] [Second Embodiment] Referring to FIG. 2, the second embodiment will be described. FIG. 2 is a cross-sectional schematic diagram for explaining the photodiode according to the second embodiment.

[0027] The fourth surface 15b of the n+-type semiconductor layer 15 has a first portion 15b2 in contact with the second electrode 16. The opposing surface of the first portion 15b2 of the fourth surface 15b is the second portion 15a2.

[0028] The third surface 14b of the n-type semiconductor layer 14 has a third portion 14b2 that contacts the second portion 15a2 of the n+-type semiconductor layer 15. A non-through groove 141 is formed in the third portion 14b2.

[0029] The non-through groove 141 is formed on the anode side with respect to the second electrode 16. The non-through groove 141 is formed, for example, in an annular shape. The cylindrical portion 151 of the n+-type semiconductor layer 15 is located in the non-through groove 141. The cylindrical portion 151 is annularly arranged at the peripheral portion of the photodiode 1. The tip portion 141a on the anode side of the non-through groove 141 is preferably located on the anode side of the second surface 13b of the p+-type semiconductor layer 13. The tip portion 141a on the anode side of the non-through groove 141 does not reach the surface protective film 12.

[0030] In this embodiment, a non-through groove 141 is formed in the third portion 14b2 of the third surface 14b of the n-type semiconductor layer 14. In this embodiment, the non-through groove 141 is formed from the fourth surface 15b side, which is the incident surface, for each pixel unit. In this embodiment, since the grooves partition the pixels, it is possible to achieve isolation of the photocurrent. Since this embodiment has the non-through groove 141, it is possible to suppress the leakage current.

[0031] With such a configuration, when forming a photodiode array using the configuration of this embodiment, interference between pixels can be reduced. Since the leakage current is suppressed in this embodiment, the dark current of adjacent pixels can be suppressed.

[0032] The embodiments disclosed in this application can be modified without departing from the gist and scope of the invention. Furthermore, the embodiments disclosed in this application and their modified examples can be appropriately combined.

[0033] Descriptions have been made regarding the characteristic embodiments in order to fully and clearly disclose the technology according to the appended claims. However, the appended claims should not be limited to the above embodiments, but should be configured to embody all modified examples and alternative configurations that can be created by those skilled in the art within the scope of the basic matters shown in this specification.

[0034] (Modified Example) In the above description, the non-through groove 141 has been described as being annular, but it is not limited to this. The non-through groove 141 may have a part of its circumferential direction interrupted. Also, in the above description, the n+-type semiconductor layer 15 had the cylindrical portion 151 located in the non-through groove 141. However, the n+-type semiconductor layer 15 may not have the cylindrical portion 151. In this case, the material forming the n+-type semiconductor layer 15 and the material forming the cylindrical portion corresponding to the cylindrical portion 151 located in the non-through groove 141 may be different. And, for example, a layer containing SiO2, MgO or MgSiO x may be formed on the cylindrical portion. Also, an air layer may be formed on the cylindrical portion corresponding to the cylindrical portion 151 located in the non-through groove 141.

Explanation of Reference Numerals

[0035] 1 Photodiode 11 First Electrode 12 Surface Protection Film 13 p+-type Semiconductor Layer 13a First Surface 13b Second Surface 14 n-type Semiconductor Layer 14b Third Surface 15 n+-type Semiconductor Layer 15b Fourth Surface 16 Second Electrode

Claims

1. a p+-type semiconductor layer having a first surface that contacts a first electrode and a surface protection film located at a peripheral portion of the first electrode; an n-type semiconductor layer that contacts a second surface of the p+-type semiconductor layer facing the first surface; an n+-type semiconductor layer that contacts a third surface of the n-type semiconductor layer facing a surface in contact with the second surface; a second electrode that contacts a fourth surface of the n+-type semiconductor layer facing a surface in contact with the third surface; characterized by comprising; The p+-type semiconductor layer, the n-type semiconductor layer, and the n+-type semiconductor layer contain Mg ２ Si, the fourth surface of the n+-type semiconductor layer has a portion that does not contact the second electrode; a photodiode.

2. the first electrode contains NiAu; infrared light is incident from a portion of the fourth surface of the n+-type semiconductor layer that does not contact the second electrode; the first electrode reflects the infrared light at a portion that contacts the first surface of the p+-type semiconductor layer; the photodiode according to Claim 1.

3. the p+-type semiconductor layer is doped with Ag; the photodiode according to Claim 1 or 2.

4. the n+-type semiconductor layer is doped with Al, boron, or phosphorus; the photodiode according to any one of Claims 1 to 3.

5. the fourth surface of the n+-type semiconductor layer has a first portion that contacts the second electrode; a non-through groove is formed in a third portion of the third surface of the n-type semiconductor layer that contacts a second portion that is an opposing surface of the first portion of the n+-type semiconductor layer; the photodiode according to any one of Claims 1 to 4.

6. The non-through groove forms an n+ semiconductor layer containing Mg ２ Si the photodiode according to Claim 5.

7. The non-through groove forms a layer containing SiO ２ , MgO or MgSiO ｘ , or an air layer. the photodiode according to Claim 5.

8. an optical sensing device comprising the photodiode according to any one of Claims 1 to 7.

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