Light-receiving element and method for manufacturing the same

Abstract

The present invention provides a photodetector capable of reducing dark current and surface leakage current, and a method for manufacturing the same. [Solution] A photodetector comprising a first semiconductor layer having a first conductivity type, a second semiconductor layer having a second conductivity type, a light absorption layer, and a first passivation film, wherein the first semiconductor layer, the light absorption layer, and the second semiconductor layer are stacked in this order to form a mesa, and the first passivation film covers the mesa and is made of an antimony semiconductor.

Description

[Technical Field]

[0001] This disclosure relates to a photodetector and a method for manufacturing the same. [Background technology]

[0002] A passivation film is provided on the surface of the photodetector. For example, the passivation film is an indium phosphate film and a silicon nitride film (Patent Documents 1 and 2). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2012-248649 [Patent Document 2] International Publication No. 2009 / 081585 [Overview of the project] [Problems that the invention aims to solve]

[0004] However, because indium phosphide has a small band gap, electrons are easily excited in the indium phosphide passivation film. This excitation of electrons may lead to an increase in dark current. On the other hand, interface states are generated at the interface between the silicon nitride passivation film and the semiconductor layer, which may lead to an increase in surface leakage current. Therefore, the objective is to provide a photodetector and a method for manufacturing the same that can reduce both dark current and surface leakage current. [Means for solving the problem]

[0005] The photodetector according to this disclosure comprises a first semiconductor layer having a first conductivity type, a second semiconductor layer having a second conductivity type, a light absorption layer, and a first passivation film, wherein the first semiconductor layer, the light absorption layer, and the second semiconductor layer are stacked in this order to form a mesa, and the first passivation film covers the mesa and is made of an antimony semiconductor.

Advantages of the Invention

[0006] According to the present disclosure, it is possible to provide a light-receiving element capable of reducing dark current and surface leakage current and a method for manufacturing the same.

Brief Description of the Drawings

[0007] [Figure 1] FIG. 1 is a plan view illustrating a light-receiving element according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view illustrating a light-receiving element. [Figure 3A] FIG. 3A is a cross-sectional view illustrating a method for manufacturing a light-receiving element. [Figure 3B] FIG. 3B is a cross-sectional view illustrating a method for manufacturing a light-receiving element. [Figure 3C] FIG. 3C is a cross-sectional view illustrating a method for manufacturing a light-receiving element. [Figure 4A] FIG. 4A is a cross-sectional view illustrating a method for manufacturing a light-receiving element. [Figure 4B] FIG. 4B is a cross-sectional view illustrating a method for manufacturing a light-receiving element. [Figure 4C] FIG. 4C is a cross-sectional view illustrating a method for manufacturing a light-receiving element. [Figure 5] FIG. 5 is a cross-sectional view illustrating a light-receiving element according to a second embodiment. [[ID=3S]] [Figure 6A] FIG. 6A is a cross-sectional view illustrating a method for manufacturing a light-receiving element. [Figure 6B] FIG. 6B is a cross-sectional view illustrating a method for manufacturing a light-receiving element. [Figure 6C] FIG. 6C is a cross-sectional view illustrating a method for manufacturing a light-receiving element.

Modes for Carrying Out the Invention

[0008] [Description of Embodiments of the Present Disclosure] First, the contents of the embodiments of the present disclosure will be listed and described.

[0009] One embodiment of the present disclosure includes: (1) a first semiconductor layer having a first conductivity type, a second semiconductor layer having a second conductivity type, a light absorption layer, and a first passivation film. The first semiconductor layer, the light absorption layer, and the second semiconductor layer are stacked in this order to form a mesa. The first passivation film covers the mesa and is a light-receiving element formed of an antimony-based semiconductor. Compared with indium phosphide and the like, the antimony-based passivation film has a large bandgap. The dark current can be reduced. Interface levels are less likely to occur at the interface between the antimony-based passivation film and the mesa, and the surface leakage current can be reduced. (2) In the above (1), the first passivation film may be formed of aluminum gallium arsenide antimony. Since the bandgap of the first passivation film is large, the dark current can be reduced. (3) In the above (1) or (2), the light absorption layer may be formed of an antimony-based semiconductor. Both the passivation film and the light absorption layer are antimony-based semiconductors, and interface levels are less likely to occur at their interfaces, and the surface leakage current can be reduced. (4) In any one of the above (1) to (3), the light-receiving element may be an avalanche photodiode. By reducing the dark current and the surface leakage current, the light-receiving sensitivity can be increased. (5) In the above (4), a multiplication layer laminated on the light absorption layer and included in the mesa may be provided, and the multiplication layer may be formed of an antimony-based semiconductor. Interface levels are less likely to occur, and the surface leakage current can be reduced. (6) In any one of the above (1) to (5), the first semiconductor layer and the second semiconductor layer may include a semiconductor layer formed of an antimony-based semiconductor. Interface levels are less likely to occur, and the surface leakage current can be reduced. (7) In any one of the above (1) to (6), a second passivation film covering the first passivation film may be provided. The light-receiving element can be effectively protected by the two passivation films. (8) A method for manufacturing a photodetector, comprising the steps of: stacking a first semiconductor layer having a first conductivity type, a light absorption layer, and a second semiconductor layer having a second conductivity type in this order; forming a mesa including the first semiconductor layer, the light absorption layer, and the second semiconductor layer; and forming a passivation film made of an antimony semiconductor to cover the mesa. Compared to indium phosphide and the like, the antimony passivation film has a large band gap. Dark current can be reduced. Interface states are less likely to occur at the interface between the antimony passivation film and the mesa, and surface leakage current can be reduced. (9) In (8) above, the step of forming the passivation film may be a step of forming the passivation film by metal-organic vapor deposition or molecular beam epitaxy. The adhesion of the passivation film to the mesa is improved.

[0010] [Details of the embodiments of this disclosure] Specific examples of light-receiving elements and methods for manufacturing the same according to embodiments of this disclosure will be described below with reference to the drawings. However, this disclosure is not limited to these examples and is intended to include all modifications within the meaning and scope of the claims as indicated by the claims.

[0011] <First Embodiment> Figure 1 is a plan view illustrating a photodetector 100 according to an embodiment. Figure 2 is a cross-sectional view illustrating the photodetector 100, showing a cross-section along line AA in Figure 1. The photodetector 100 is formed of a III-V compound semiconductor and is an avalanche photodiode (APD), used, for example, for detecting near-infrared light. The top surface of the photodetector 100 is parallel to the XY plane. Two sides of the photodetector 100 are parallel to the X axis. The other two sides are parallel to the Y axis. The Z axis is in the thickness direction. The X, Y, and Z axes are orthogonal to each other.

[0012] As shown in Figures 1 and 2, the photodetector 100 has a mesa 10, an electrode 12, an electrode 14, and a terrace 16. The mesa 10 is, for example, frustoconical in shape and is located in the center of the photodetector 100. The diameter D1 of the upper surface of the mesa 10 is, for example, 50 μm or more and 500 μm or less. The terrace 16 is located outside the mesa 10. The terrace 16 is a planar portion and is parallel to the XY plane.

[0013] In Figure 1, electrodes 12 and 14 are indicated by diagonal lines. Electrode 12 has a square ring shape and is provided on the terrace 16, surrounding the mesa 10. Electrode 14 has an arc shape (C-shape) and is provided on the mesa 10. The central part of the upper surface of the mesa 10 is not covered by electrode 14 and functions as a light-receiving area 11.

[0014] As shown in Figure 2, the photodetector 100 includes a substrate 20, a buffer layer 22 (first semiconductor layer), a light absorption layer 24, a semiconductor layer 26, a multiplier layer 28, a semiconductor layer 30 (second semiconductor layer), and a contact layer 32 (second semiconductor layer). The outer periphery of the buffer layer 22 in the XY plane is included in the terrace 16. The central part of the buffer layer 22 protrudes in the Z-axis direction from the outer periphery of the buffer layer 22. The light absorption layer 24, semiconductor layer 26, multiplier layer 28, and semiconductor layer 30 are stacked in this order on the protruding part of the buffer layer 22. An arc-shaped contact layer 32 is stacked on the semiconductor layer 30.

[0015] The mesa 10 includes a light-absorbing layer 24, a semiconductor layer 26, a multiplier layer 28, a semiconductor layer 30, and a contact layer 32. The mesa 10 protrudes further in the Z-axis direction than the terrace 16 and has a forward mesa shape. The sides of the mesa 10 are formed by the light-absorbing layer 24, the semiconductor layer 26, the multiplier layer 28, and the semiconductor layer 30. The sides of the mesa 10 are inclined with respect to the Z-axis direction. The top surface of the mesa 10 is formed by the semiconductor layer 30.

[0016] The passivation film 34 (first passivation film) covers the surface of the terrace 16, covers the side and upper surfaces of the mesa 10, contacts the surface of the terrace 16, and contacts the side and upper surfaces of the mesa 10. The passivation film 34 has an opening on the terrace 16 and also has an opening on the mesa 10. The electrode 12 is provided on the terrace 16 and is electrically connected to the buffer layer 22 through the opening of the passivation film 34. The electrode 14 is provided on the mesa 10 and is electrically connected to the contact layer 32 through the opening of the passivation film 34.

[0017] The substrate 20 is a semi-insulating semiconductor substrate and is formed of, for example, gallium antimonide (GaSb) or indium phosphide (InP). The buffer layer 22 is formed of, for example, n+-type (first conductivity type) gallium antimonide ((n+)-GaSb) or n+-type indium gallium arsenide ((n+)-InGaAs). The thickness of the central portion of the buffer layer 22 is, for example, 1000 nm or more and 2000 nm or less. The buffer layer 22 is doped with impurities such as silicon (Si). The impurity concentration is, for example, 1×10 19 cm -3 or more and 3×10 19 cm -3 or less.

[0018] The light absorption layer 24 is a bulk semiconductor and is formed of, for example, undoped gallium arsenide antimonide (i-GaAsSb) or indium gallium arsenide (i-InGaAs). The thickness of the light absorption layer 24 is, for example, 100 nm or more and 3000 nm or less.

[0019] The multiplication layer 28 is formed of, for example, undoped Al x Ga 1-x As y Sb 1-y To be lattice-matched with the substrate 20 and the like, the composition ratio x of Al and the composition ratio y of As are determined. For example, x is 0.4 or more and 1 or less. An example of the multiplication layer 28 is Al 0·85 Ga 0.15 As 0.56 Sb 0.44The thickness of the multiplier layer 28 is, for example, 50 nm or more and 1500 nm or less.

[0020] The semiconductor layers 26 and 30 are formed of, for example, p-type (second conductivity type) AlGaAsSb. The thickness of each of the semiconductor layers 26 and 30 is, for example, 100 nm or more and 500 nm or less. The contact layer 32 is formed of, for example, p+-type GaSb or indium gallium arsenide (InGaAs). The thickness of the contact layer 32 is, for example, 10 nm or more and 100 nm or less.

[0021] The passivation film 34 is formed of an antimony-based (Sb-based) III-V compound semiconductor. An Sb-based semiconductor is a semiconductor containing antimony (Sb). For example, the passivation film 34 is i-Al x Ga 1-x As y S 1-y It is formed of Al. The composition ratio x of Al and the composition ratio y of As are determined to match the lattice with the substrate 20, etc. For example, x is between 0.4 and 1. The passivation film 34 is made of Al, for example. 0·85 Ga 0.15 As 0.56 S 0.44 The thickness of the passivation film 34 is, for example, 50 nm or more and 1000 nm or less. The band gap of the passivation film 34 is, for example, 1.59 eV.

[0022] Electrodes 12 and 14 are made of metal. Electrode 12 is made by laminating a titanium (Ti) layer, a platinum (Pt) layer, and a gold (Au) layer, for example, from the side closest to the buffer layer 22. Electrode 14 is made by laminating a Ti layer, a Pt layer, and an Au layer, for example, from the side closest to the contact layer 32. Electrodes 12 and 14 may also be laminates of Ti and Au layers.

[0023] Mesa 10 has an n-type buffer layer 22, a light absorption layer 24, a p-type semiconductor layer 26, a semiconductor layer 30, and a contact layer 32 stacked on top of each other. A PIN (positive-intrinsic-negative) junction is formed from top to bottom in Figure 1.

[0024] The photodetector 100 is a top-incident type photodiode and detects light incident on the light-receiving region 11 from above as shown in Figure 2. The light to be detected is, for example, near-infrared light. When in use, a reverse bias voltage is applied to the photodetector 100. A positive voltage is applied to electrode 12 and a negative voltage is applied to electrode 14. A depletion region is generated in the mesa 10. The light-absorbing layer 24 absorbs, for example, near-infrared light and generates carriers (electron-hole pairs). The carriers move due to the electric field in the depletion region. Electrons collide with atoms in the multiplier layer 28, electrons are emitted from the atoms, and the number of electrons increases. The amplified carriers are output as a photocurrent.

[0025] (Manufacturing method) Figures 3A to 4C are cross-sectional views illustrating a method for manufacturing the photodetector 100. As shown in Figure 3A, for example, a buffer layer 22, a light absorption layer 24, a semiconductor layer 26, a multiplier layer 28, a semiconductor layer 30, and a contact layer 32 are epitaxially grown on one surface of the substrate 20 in this order, using methods such as metal-organic chemical vapor deposition (MOCVD) or molecular beam epitaxy (MBE).

[0026] As shown in Figure 3B, the contact layer 32 is formed into an arc shape by wet etching or dry etching. As shown in Figure 3C, wet etching or dry etching is performed from the semiconductor layer 30 to a portion of the buffer layer 22 to form the mesa 10 and terrace 16.

[0027] As shown in Figure 4A, a passivation film 34 is formed, for example, by MOCVD or MBE.

[0028] As shown in Figure 4B, openings are formed in the portion of the passivation film 34 above the terrace 16 by wet etching or dry etching, and openings are also formed in the portion of the passivation film 34 above the mesa 10. As shown in Figure 4C, electrodes 12 and 14 are formed by vacuum deposition and lift-off. The photodetector 100 is then formed.

[0029] According to the first embodiment, the buffer layer 22, the light absorption layer 24, the semiconductor layer 26, the multiplier layer 28, the semiconductor layer 30, and the contact layer 32 form the mesa 10. The passivation film 34 covers the sides and top surface of the mesa 10 and covers the surface of the terrace 16. The passivation film 34 is made of an antimony semiconductor. The band gap of the passivation film 34 is larger than the band gap of the InP film (1.35 eV). Because the passivation film 34 has a large band gap, carriers are less likely to be generated from the passivation film 34, and dark current can be reduced.

[0030] The Sb-based semiconductor passivation film 34 covers the mesa 10 and is in contact with the side and top surfaces of the mesa 10. Compared to the interface between SiN and the mesa 10, interface states are less likely to occur at the interface between the Sb-based passivation film 34 and the mesa 10. Surface leakage current can be reduced.

[0031] As shown in Figure 4A, after the formation of the mesa 10, a passivation film 34 is deposited, for example, by MOCVD or MBE. Due to the surfactant effect, the Sb-based semiconductor passivation film 34 adheres well to the semiconductor of the photodetector 100. The adhesion of the passivation film 34 is improved, and the photodetector 100 can be protected by the passivation film 34.

[0032] The passivation film 34 is formed from an Sb-based semiconductor, for example, AlGaAsSb. The bandgap of the AlGaAsSb passivation film 34 is 1.59 eV, which is larger than the bandgap of InP (1.35 eV). Dark current can be effectively reduced.

[0033] The mesa 10 may include an Sb-based semiconductor layer. The light absorption layer 24 may be formed of an Sb-based semiconductor such as GaAsSb or InGaAsSb. The passivation film 34 covers the light absorption layer 24. Interface states are less likely to occur at the interface between Sb-based semiconductors, and surface leakage current can be reduced. The adhesion of the passivation film 34 is improved.

[0034] The photodetector 100 is an avalanche photodiode, and high light-receiving sensitivity is required. By using an Sb-based semiconductor passivation film 34, it is possible to reduce the dark current and surface leakage current and improve light-receiving sensitivity.

[0035] The multiplier layer 28 may be formed of an Sb-based semiconductor such as AlGaAsSb. Interface states are less likely to occur at the interface between Sb-based semiconductors, and surface leakage current can be reduced. The multiplier layer 28 may be provided between the light absorption layer 24 and the contact layer 32, or between the light absorption layer 24 and the buffer layer 22.

[0036] A p-type semiconductor layer 30 and a contact layer 32 are stacked on the multiplier layer 28. A p-type semiconductor layer 26 is stacked between the multiplier layer 28 and the light absorption layer 24. A high electric field is applied to the multiplier layer 28. Carriers are accelerated by the high electric field and collide with atoms in the multiplier layer 28. The carriers are multiplied, and the sensitivity is improved.

[0037] The buffer layer 22, semiconductor layer 26, semiconductor layer 30, and contact layer 32 may be formed from Sb-based semiconductors. Since interface states are less likely to occur at the interface with the passivation film 34, surface leakage current can be reduced. The adhesion of the passivation film 34 is improved.

[0038] By stacking Sb-based semiconductors, a lattice-matched semiconductor layer can be formed. The characteristics of the photodetector 100 become stable. The buffer layer 22, light absorption layer 24, semiconductor layer 26, multiplier layer 28, semiconductor layer 30, and contact layer 32 may be formed from compound semiconductors other than Sb-based semiconductors. The photodetector 100 may also be a photodiode other than an avalanche photodiode.

[0039] In the example above, a pin junction is formed from top to bottom in Figure 1. A nip junction may also be formed from top to bottom. The contact layer 32, semiconductor layer 30, and semiconductor layer 26 are n-type. The buffer layer 22 is p-type.

[0040] The first embodiment may also be applied to an array-type photodetector. In an array-type photodetector, multiple mesas are arranged, for example, in a two-dimensional grid. Each mesa 10 functions as a single photodiode. The photodiodes are separated by recesses between adjacent mesas 10. Multiple mesas 10 are covered with an Sb-based passivation film 34.

[0041] <Second Embodiment> Figure 5 is a cross-sectional view illustrating a light-receiving element 200 according to the second embodiment. The same configuration as in the first embodiment will not be described.

[0042] As shown in Figure 5, the photodetector 200 has a passivation film 34 (first passivation film) and a passivation film 36 (second passivation film). The passivation film 34 is formed of an Sb-based semiconductor such as AlGaAsSb and is in contact with the side and top surfaces of the mesa 10. The passivation film 36 is formed of an insulator such as silicon nitride (SiN) or silicon oxide (SiO2). The passivation film 36 covers the passivation film 34.

[0043] Figures 6A to 6C are cross-sectional views illustrating a method for manufacturing the photodetector 200. The steps from Figures 3A to 4A are also performed in the second embodiment. As shown in Figure 6A, for example, a passivation film 36 is formed on the surface of the passivation film 34 by plasma CVD (PECVD).

[0044] As shown in Figure 6B, openings are formed in the passivation films 36 and 34 on the terrace 16 by wet etching or dry etching, and also in the portion above the mesa 10. As shown in Figure 6C, electrodes 12 and 14 are formed by vacuum deposition and lift-off. The photodetector 200 is then formed.

[0045] According to the second embodiment, the passivation film 34 and the passivation film 36 are deposited in this order. The passivation film 34 is provided between the passivation film 36 and the mesa 10. The passivation film 36 does not come into contact with the mesa 10. Interface states are less likely to occur between the Sb-based passivation film 34 and the mesa 10. Surface leakage current can be reduced. Because the passivation film is doubled, the photodetector 200 can be effectively protected from moisture and the like.

[0046] Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to these specific embodiments, and various modifications and changes are possible within the scope of the gist of this disclosure as described in the claims. [Explanation of Symbols]

[0047] 10 Mesa 11 Light receiving area 12, 14 electrodes 20 circuit boards 22 Buffer Layers 24 Light-absorbing layer 26, 30 Semiconductor layer 28 Multiplier Layers 32 Contact Layers 34, 36 Passivation membrane 100, 200 photodetectors

Claims

1. A first semiconductor layer having a first conductivity type, A second semiconductor layer having a second conductivity type, Light-absorbing layer, A first passivation membrane is provided, The first semiconductor layer, the light-absorbing layer, and the second semiconductor layer are stacked in this order to form a mesa. The first passivation film covers the mesa and is a photodetector made of an antimony semiconductor.

2. The photodetector according to claim 1, wherein the first passivation film is formed of aluminum gallium arsenide antimony.

3. The photodetector according to claim 1 or claim 2, wherein the light-absorbing layer is formed of an antimony semiconductor.

4. The light-receiving element according to claim 1 or claim 2, wherein the light-receiving element is an avalanche photodiode.

5. The light-absorbing layer is laminated and comprises a multiplier layer contained in the mesa, The photodetector according to claim 4, wherein the multiplier layer is formed of an antimony semiconductor.

6. The photodetector according to claim 1 or claim 2, wherein the first semiconductor layer and the second semiconductor layer include semiconductor layers formed of an antimony semiconductor.

7. The photodetector according to claim 1 or claim 2, further comprising a second passivation film covering the first passivation film.

8. A step of stacking a first semiconductor layer having a first conductivity type, a light absorption layer, and a second semiconductor layer having a second conductivity type in this order, A step of forming a mesa including the first semiconductor layer, the light-absorbing layer, and the second semiconductor layer, A method for manufacturing a photodetector, comprising the step of covering the mesa and forming a passivation film made of an antimony semiconductor.

9. The method for manufacturing a photodetector according to claim 8, wherein the step of forming the passivation film is a step of forming the passivation film by metal-organic vapor deposition or molecular beam epitaxy.

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