Light receiving element

Abstract

To provide a light receiving element with high light receiving sensitivity.SOLUTION: A light receiving element includes a semiconductor substrate, and a light-receiving film provided on the semiconductor substrate and having a narrower bandgap than the semiconductor substrate. The semiconductor substrate has a first polarity layer of a first conductivity type provided at a position exposed on the upper surface. The light-receiving film includes a second polar layer of a second conductivity type different from the first conductivity type, and a boundary layer provided at a position in contact with the first polar layer of the semiconductor substrate, disposed between the second polar layer and the first polar layer of the semiconductor substrate, and containing impurities of a first conductivity type.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The technology disclosed in this specification relates to a light receiving element. [Background technology]

[0002] Patent Document 1 discloses a photodetector comprising a semiconductor substrate made of n-type silicon and a photodetector film made of p-type germanium provided on the semiconductor substrate. In this photodetector, a depletion layer is formed at the pn junction between the semiconductor substrate and the photodetector film. When light is irradiated onto the depletion layer, photoexcited electrons and holes are generated. The generated electrons and holes are separated by an electric field applied to the depletion layer and extracted to an external circuit as photocurrent. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-22619 Summary of the Invention [Problem to be solved by the invention]

[0004] The semiconductor substrate and the light-receiving film are made of different materials. Therefore, the light-receiving film side of the pn junction between the semiconductor substrate and the light-receiving film contains a large number of crystal defects due to lattice mismatch. These crystal defects can act as acceptors. Therefore, a P-type region with a high carrier concentration is formed in the light-receiving film at the pn junction. Such a P-type region with a high carrier concentration in the light-receiving film suppresses the expansion of the depletion layer into the light-receiving film, causing a decrease in light-receiving sensitivity. The present specification aims to provide a light-receiving element with high light-receiving sensitivity. [Means for solving the problem]

[0005] The photodetector disclosed herein may include a semiconductor substrate and a photodetector film disposed on the semiconductor substrate and having a narrower bandgap than the semiconductor substrate. The semiconductor substrate includes a first polarity layer of a first conductivity type disposed at a position exposed on the upper surface. The photodetector film includes a second polarity layer of a second conductivity type different from the first polarity type, and a boundary layer containing first-conductivity impurities disposed in contact with the first polarity layer of the semiconductor substrate and disposed between the second polarity layer and the first polarity layer of the semiconductor substrate. In this photodetector, the first-conductivity impurities contained in the boundary layer can reduce carrier concentration increases due to crystal defects in the photodetector film. This allows the depletion layer to extend widely in the photodetector film, improving photodetector sensitivity.

[0006] The density of crystal defects contained in the boundary layer may decrease from a position in contact with the first polarity layer of the semiconductor substrate toward the second polarity layer. In other words, the boundary layer is provided in a range of the light-receiving film where the density of crystal defects changes, i.e., in a range where the density of crystal defects is high. By providing the boundary layer in such a position, it is possible to reduce the carrier concentration that increases due to crystal defects in the light-receiving film. Furthermore, the concentration of the first conductivity type impurity contained in the boundary layer may decrease from a position in contact with the first polarity layer of the semiconductor substrate toward the second polarity layer. This light-receiving element can prevent the first conductivity type impurity from being excessively introduced into the boundary layer.

[0007] The boundary layer may be of the first conductivity type. When the boundary layer is of the first conductivity type, a depletion layer is formed at the interface between the boundary layer and the second polarity layer in the light-receiving film. Therefore, in this light-receiving element, the depletion layer is formed in an area with few crystal defects, which suppresses recombination of photoexcited electrons and holes and extends the lifetime of the electrons and holes.

[0008] The first conductivity type may be n-type. The second conductivity type may be i-type or p-type. The semiconductor substrate may be a silicon substrate. The light-receiving film may be composed of a germanium film, a germanium tin film, or a multilayer film combining these. Furthermore, the first conductivity type impurity contained in the boundary layer may be phosphorus, arsenic, antimony, or a combination thereof. [Brief explanation of the drawings]

[0009] [Figure 1] (A) is a plan view of the light receiving element, (B) is a cross-sectional view corresponding to the line BB in (A). [Figure 2] 1A and 1B are enlarged views of the main part of the portion where the cathode layer, the boundary layer, and the anode layer are stacked, and a diagram showing the distribution of the density of crystal defects contained in the boundary layer and the anode layer. [Figure 3] 3A to 3C are diagrams illustrating a first manufacturing process of the light-receiving element. [Figure 4] 3A to 3C are diagrams illustrating a first manufacturing process of the light-receiving element. [Figure 5] 3A to 3C are diagrams illustrating a first manufacturing process of the light-receiving element. [Figure 6] 3A to 3C are diagrams illustrating a first manufacturing process of the light-receiving element. [Figure 7] 10A to 10C are diagrams illustrating a second manufacturing process of the light-receiving element. [Figure 8] 10A to 10C are diagrams illustrating a second manufacturing process of the light-receiving element. [Figure 9] 10A to 10C are diagrams illustrating a second manufacturing process of the light-receiving element. [Figure 10] 10A to 10C are diagrams illustrating a second manufacturing process of the light-receiving element. DETAILED DESCRIPTION OF THE INVENTION

[0010] As shown in FIG. 1, the light-receiving element 1 includes a semiconductor substrate 10, an insulating layer 20, a light-receiving film 30, an anode electrode 40, and a cathode electrode 50.

[0011] The semiconductor substrate 10 is not particularly limited, but may be, for example, a silicon substrate. The semiconductor substrate 10 includes an N-type cathode layer 12 and an N + The cathode layer 12 has a P-type contact region 14 and a P-type connection region 16. The cathode layer 12 is an example of a first polarity layer.

[0012] The cathode layer 12 is the portion of the semiconductor substrate 10 excluding the contact region 14 and the connection region 16. The N-type impurity contained in the cathode layer 12 is not particularly limited, but may be, for example, phosphorus. The cathode layer 12 has a portion exposed on the upper surface of the semiconductor substrate 10, and this portion is in contact with the light-receiving film 30.

[0013] The contact region 14 is provided at a position exposed on the upper surface of the semiconductor substrate 10, is in contact with the cathode layer 12, and is a region having a higher concentration of N-type impurities than the cathode layer 12. The impurities contained in the contact region 14 are not particularly limited, but may be, for example, phosphorus or arsenic. The contact region 14 is in contact with the cathode electrode 50.

[0014] The connection region 16 is provided at a position exposed on the upper surface of the semiconductor substrate 10, and is arranged so as to surround the portion of the cathode layer 12 that contacts the light-receiving film 30. In the plan view of FIG. 1(A), the position of the side surface of the connection region 16 is indicated by a dashed line. In plan view, the connection region 16 has a roughly fan-shaped outer shape, and a portion of the circular cathode layer 12 is arranged inside the connection region 16. The impurity contained in the connection region 16 is not particularly limited, but may be, for example, boron. The connection region 16 contacts both the light-receiving film 30 and the anode electrode 40, electrically connecting them.

[0015] The insulating layer 20 is provided to cover the upper surface of the semiconductor substrate 10. The insulating layer 20 has a plurality of openings 21, 22, 23, and 24 formed therein. In the plan view of FIG. 1A, the side surfaces of the first opening 21 and the second opening 22 are indicated by dashed lines, and the areas of the first opening 21 and the second opening 22 are indicated by gray. The first opening 21 is formed to coincide with the center of the light-receiving film 30 in plan view. The cathode layer 12 is exposed through the first opening 21. The second opening 22 is formed to extend along the side surface of the light-receiving film 30, slightly inward from the side surface of the light-receiving film 30. The connection region 16 is exposed through the second opening 22. The insulating layer 20 is not particularly limited, and may be, for example, silicon oxide.

[0016] The light-receiving film 30 is provided on the semiconductor substrate 10 via the insulating layer 20. In plan view, the light-receiving film 30 is disposed between the anode electrode 40 and the cathode electrode 50, and is spaced apart from the anode electrode 40 and the cathode electrode 50. In plan view, the light-receiving film 30 has a circular shape centered on the first opening 21 of the insulating layer 20. The light-receiving film 30 is made of a material with a band gap narrower than that of the semiconductor substrate 10. The material is not particularly limited, and may be, for example, a germanium (Ge) film. Alternatively, the light-receiving film 30 may be made of a germanium tin (GeSn) film, or may be a multilayer film combining a germanium film and a germanium tin film. When the light-receiving film 30 is made of such a narrow band gap semiconductor, it can be sensitive to light in the eye-safe band (light of 1300 nm to 1600 nm).

[0017] The light-receiving film 30 has an anode layer 32 and a boundary layer 34. The anode layer 32 is the portion of the light-receiving film 30 excluding the boundary layer 34, and is either i-type or p-type. The anode layer 32 contacts the connection region 16 of the semiconductor substrate 10 through the second opening 22 of the insulating layer 20. This electrically connects the anode layer 32 and the connection region 16. The anode layer 32 is an example of a second polarity layer.

[0018] The boundary layer 34 is a portion of the light-receiving film 30 into which N-type impurities have been selectively introduced, and is provided at a position in contact with the cathode layer 12 of the semiconductor substrate 10, and is disposed between the anode layer 32 and the cathode layer 12 of the semiconductor substrate 10. The boundary layer 34 is selectively provided within the first opening 21 of the insulating layer 20. The concentration profile of the N-type impurities introduced into the boundary layer 34 may be constant in the thickness direction, or may vary in the thickness direction, as will be described later.

[0019] 2 shows an enlarged view of a main portion of the laminated portion of the cathode layer 12 of the semiconductor substrate 10, the boundary layer 34 of the light-receiving film 30, and the anode layer 32. Furthermore, FIG. 2 also shows the distribution of the density of crystal defects in the boundary layer 34 of the light-receiving film 30 and the anode layer 32 in the thickness direction.

[0020] As will be described later, the light-receiving film 30 is formed on the upper surface of the semiconductor substrate 10 using a deposition technique. As a result, a large number of lattice defects are formed on the light-receiving film 30 side of the junction between the semiconductor substrate 10 and the light-receiving film 30 due to a lattice mismatch between silicon, which is the material of the semiconductor substrate 10, and germanium, which is the material of the light-receiving film 30. The defect density in the light-receiving film 30 is highest at the position in contact with the semiconductor substrate 10 and decreases with increasing distance from the semiconductor substrate 10. At a sufficient distance from the semiconductor substrate 10, the defect density in the light-receiving film 30 is roughly constant. The boundary layer 34 is arranged to include at least a portion of the range where the defect density changes, i.e., the range where crystal defects increase due to the lattice mismatch.

[0021] The lattice defects contained in the boundary layer 34 can act as acceptors. Therefore, for example, if the boundary layer 34 is not provided, the P-type carrier concentration will be high in the portion of the light-receiving film 30 in contact with the semiconductor substrate 10 due to an increase in the acceptor concentration caused by the lattice defects. On the other hand, in the light-receiving element 1, the boundary layer 34 is provided in an area with a high defect density. The boundary layer 34 is doped with N-type impurities such as phosphorus, arsenic, antimony, or a combination thereof. Therefore, the boundary layer 34 can reduce the carrier concentration that increases due to lattice defects. The boundary layer 34 may be N-type or P-type depending on the concentration of the N-type impurities doped. In this example, the boundary layer 34 is P-type.

[0022] Returning to FIG. 1 , the anode electrode 40 is provided on the insulating layer 20, including the anode electrode opening 23 in the insulating layer 20, and is in contact with the connection region 16 through the anode electrode opening 23. In this manner, the anode electrode 40 is electrically connected to the anode layer 32 of the light-receiving film 30 through the connection region 16. The anode electrode 40 is not particularly limited, but may be made of aluminum, for example.

[0023] The cathode electrode 50 is provided on the insulating layer 20, including the cathode electrode opening 24 in the insulating layer 20, and is in contact with the contact region 14 through the cathode electrode opening 24. In this manner, the cathode electrode 50 is electrically connected to the cathode layer 12 through the contact region 14. The cathode electrode 50 is not particularly limited, and may be made of aluminum, for example.

[0024] (Operation when light is received by light receiving element 1) When a voltage is applied between the anode electrode 40 and the cathode electrode 50 such that the cathode electrode 50 is more positive than the anode electrode 40, the pn junction between the cathode layer 12 of the semiconductor substrate 10 and the boundary layer 34 of the light-receiving film 30 is reverse-biased, causing a depletion layer to expand between them. When eye-safe light (e.g., 1550 nm, energy: 0.8 eV) is incident on the upper surface of the light-receiving film 30 and is absorbed by the depletion layer extending in the light-receiving film 30, electrons and holes are generated by photoexcitation. Due to the internal electric field of the depletion layer, the generated holes flow to the anode electrode 40 via the anode layer 32 and the connection region 16, and the generated electrons flow to the cathode electrode 50 via the cathode layer 12 and the contact region 14. In this way, in the light-receiving element 1, a photocurrent flows from the cathode electrode 50 to the anode electrode 40 based on the incident light. The light-receiving element 1 can measure the incident light based on this photocurrent.

[0025] As described above, the provision of the boundary layer 34 in the light-receiving element 1 reduces the carrier concentration that increases due to lattice defects. This allows the depletion layer to expand significantly within the light-receiving film 30 at the pn junction between the cathode layer 12 of the semiconductor substrate 10 and the boundary layer 34 of the light-receiving film 30. The expanded depletion layer within the light-receiving film 30 increases the effective light-receiving area, thereby improving the light-receiving sensitivity of the light-receiving element 1.

[0026] In the photodetector 1, the conductivity type of the boundary layer 34 may be inverted to N type by increasing the amount of N-type impurities introduced into the boundary layer 34. In this case, a depletion layer is formed at the interface between the anode layer 32 and the boundary layer 34. In this photodetector 1, the depletion layer is formed in an area with few crystal defects, which suppresses the recombination of photoexcited electrons and holes and extends the lifetime of the electrons and holes.

[0027] The density of crystal defects contained in the boundary layer 34 decreases from the position where the boundary layer 34 contacts the cathode layer 12 of the semiconductor substrate 10 toward the anode layer 32 (see FIG. 2). In the light-receiving element 1, the concentration of N-type impurities contained in the boundary layer 34 decreases from the position where the boundary layer 34 contacts the cathode layer 12 of the semiconductor substrate 10 toward the anode layer 32. That is, the profile of the N-type impurity concentration in the thickness direction is adjusted to match the profile of the crystal defect density in the thickness direction. For example, if excessive N-type impurities are introduced into the boundary layer 34 and the N-type carrier concentration in the boundary layer 34, which has been inverted to N-type, becomes too high, the depletion layer will not extend as much, resulting in a decrease in light-receiving sensitivity. On the other hand, if the profile of the crystal defect density and the profile of the N-type impurity concentration match, the introduction of excessive N-type impurities into the boundary layer 34 is suppressed. As a result, the depletion layer can expand significantly within the light-receiving film 30, improving the light-receiving sensitivity of the light-receiving element 1. The concentration of the N-type impurity contained in the boundary layer 34 may decrease continuously or in multiple steps from the position in contact with the cathode layer 12 of the semiconductor substrate 10 toward the anode layer 32.

[0028] (First manufacturing method of light receiving element 1) 3, a semiconductor substrate 10 is prepared on which a cathode layer 12, a contact region 14, and a connection region 16 are formed. An insulating layer 20 is formed on the upper surface of the semiconductor substrate 10. Next, a mask (not shown) having openings in regions corresponding to the plurality of openings 21, 22, 23, and 24 is patterned on the insulating layer 20, and the plurality of openings 21, 22, 23, and 24 are formed using an etching technique.

[0029] Next, as shown in FIG. 4 , a deposition technique is used to fill the openings 21, 22, 23, and 24 and deposit an N-type germanium film 130 on the insulating layer 20. The deposition method is not particularly limited, but may be, for example, a sputtering method, an MBE method, or a CVD method. At this time, due to a lattice mismatch between silicon, which is the material of the semiconductor substrate 10, and germanium, which is the material of the germanium film 130, a large number of lattice defects are formed on the germanium film 130 side of the junction between the semiconductor substrate 10 and the germanium film 130. The lattice defects can act as acceptors. However, since the germanium film 130 is deposited containing N-type impurities, the germanium film 130 at the junction is P-type or N-type with a low acceptor concentration. Note that an N-type germanium tin film may be deposited instead of the N-type germanium film 130.

[0030] 5, the germanium film 130 is processed using an etching technique so as to selectively leave a portion of the germanium film 130 in the first opening 21. The portion of the germanium film 130 remaining in the first opening 21 becomes the boundary layer 34.

[0031] 6, a deposition technique is used to fill the openings 21, 22, 23, and 24 and deposit an i-type or p-type germanium film 132 on the insulating layer 20. The deposition method is not particularly limited, but may be, for example, a sputtering method, an MBE method, or a CVD method. Note that instead of the i-type or p-type germanium film 132, an i-type or p-type germanium tin film may be deposited.

[0032] Thereafter, the germanium film 132 is processed using an etching technique to form the anode layer 32, and then the anode electrode 40 and the cathode electrode 50 are provided, thereby completing the light-receiving element 1.

[0033] (Second manufacturing method of light receiving element 1) First, the semiconductor substrate 10 and insulating layer 20 shown in Fig. 3 are prepared, and then, as shown in Fig. 7, a deposition technique is used to fill the openings 21, 22, 23, and 24 and to deposit an i-type or p-type germanium film 134 on the insulating layer 20. The deposition method is not particularly limited, but may be, for example, a sputtering method, an MBE method, or a CVD method. Note that, instead of the i-type or p-type germanium film 134, an i-type or p-type germanium tin film may be deposited.

[0034] Next, as shown in FIG. 8, the germanium film 134 is processed using an etching technique so that parts of the germanium film 134 are selectively left in the plurality of openings 21, 22, 23, and 24.

[0035] 9, a mask 62 is formed to expose the first opening 21 and the cathode electrode opening 24, and then, using an ion implantation technique, N-type impurities are introduced into a portion of the germanium film 134 remaining in the first opening 21 and the cathode electrode opening 24, thereby inverting the portion of the germanium film 134 to N-type. The portion of the germanium film 134 remaining in the first opening 21 becomes the boundary layer 34. After the ion implantation is completed, the mask 62 is removed.

[0036] 10, a deposition technique is used to fill the openings 21, 22, 23, and 24 and deposit an i-type or p-type germanium film 136 on the insulating layer 20. The deposition method is not particularly limited, but may be, for example, a sputtering method, an MBE method, or a CVD method. Note that instead of the i-type or p-type germanium film 136, an i-type or p-type germanium tin film may be deposited.

[0037] Thereafter, the germanium film 136 is processed using an etching technique to form the anode layer 32, and then the anode electrode 40 and the cathode electrode 50 are disposed, thereby completing the light-receiving element 1. In this manufacturing method, the i-type or P-type germanium film 134 remains in the second opening 22 and the anode electrode opening 23, and the i-type or P-type germanium film 134 inverted to N-type remains in the cathode electrode opening 24. However, the germanium film 134 remaining in the second opening 22 and the anode electrode opening 23 has the same conductivity type as the connection region 16 and can be connected to the connection region 16 with low contact resistance. The germanium film 134 remaining in the cathode electrode opening 24 has the same conductivity type as the contact region 14 and can be connected to the contact region 14 with low contact resistance.

[0038] Although specific examples of the present invention have been described in detail above, these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and variations of the specific examples exemplified above. Furthermore, the technical elements described in this specification or drawings exhibit technical utility alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. Furthermore, the technology exemplified in this specification or drawings can achieve multiple objectives simultaneously, and achieving one of these objectives itself has technical utility. [Explanation of symbols]

[0039] 1: Light receiving element, 10: Semiconductor substrate, 12: Cathode layer, 14: Contact region, 16: Connection region, 20: Insulating layer, 30: Light receiving film, 32: Anode layer, 34: Boundary layer, 40: Anode electrode, 50: Cathode electrode

Claims

1. a semiconductor substrate; a light receiving film provided on the semiconductor substrate and having a band gap narrower than that of the semiconductor substrate, The semiconductor substrate is a first polarity layer of a first conductivity type provided at a position exposed on the upper surface, The light receiving film is a second polarity layer of a second conductivity type different from the first conductivity type; a boundary layer provided in a position in contact with the first polarity layer of the semiconductor substrate, disposed between the second polarity layer and the first polarity layer of the semiconductor substrate, and containing impurities of a first conductivity type; a density of crystal defects contained in the boundary layer decreases from a position of the semiconductor substrate in contact with the first polarity layer toward the second polarity layer, a concentration of the first conductivity type impurity contained in the boundary layer decreases from a position of the semiconductor substrate in contact with the first polarity layer toward the second polarity layer;

2. 2. The light-receiving element according to claim 1, wherein the boundary layer is of the first conductivity type.

3. the first conductivity type is n-type, the second conductivity type is i-type or p-type, the semiconductor substrate is a silicon substrate, 3. The light-receiving element according to claim 1, wherein the light-receiving film is made of a germanium film, a germanium tin film, or a multilayer film of a combination of these.

4. 4. The light-receiving element according to claim 3, wherein the impurity of the first conductivity type contained in the boundary layer is phosphorus, arsenic, antimony, or a combination thereof.

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