Photoelectric conversion element

Abstract

A photoelectric conversion element (100) according to the present embodiment comprises a first laminate (10) and a first optical waveguide (20). The first laminate (10) includes: a first impurity semiconductor provided in an upper section in the lamination direction; a second impurity semiconductor that has a conductivity type which is different from that of the first impurity semiconductor and that is provided in a lower section in the lamination direction; and a first intrinsic semiconductor sandwiched between the first impurity semiconductor and the second impurity semiconductor in the lamination direction. When viewed from the lamination direction, the length of a first side (S1) of the first intrinsic semiconductor of the first laminate (10) is longer than the length of a second side (S2) that intersects the first side. The first optical waveguide (20) is connected to a first lateral surface to which the first side (S1) of the first laminate (10) belongs.

Description

photoelectric conversion element

[0001] This application claims priority to Japanese Patent Application No. 2024-012111, filed on January 30, 2024, the contents of which are incorporated herein by reference.

[0002] Advances in communications technology have created a demand for high-speed, highly efficient data transmission and reception, drawing increasing attention to silicon photonics, a technology that uses microfabrication techniques to integrate elements such as light-emitting elements, light-receiving elements, and optical modulators on a silicon substrate.

[0003] Germanium photodiodes are known as photoelectric conversion elements used in silicon photonics circuits, but they have the problem of being difficult to obtain high output due to saturation.

[0004] For example, Non-Patent Documents 1 to 3 disclose various methods for realizing a high-output photodiode. Non-Patent Document 1 discloses an example in which multiple photodiodes are used. Non-Patent Document 2 discloses an example in which a high-concentration P-type doped layer is used as an underlying layer for a germanium layer. Non-Patent Document 3 discloses an example in which a special waveguide shape is used to cause evanescent light to be incident on germanium.

[0005] Ta-Ching Tzu et al., “Foundry-Enabled High-Power Photodetectors for Microwave Photonics,” IEEE Journal of Selected Topics in Quantum Electronics 25, 3800111 (2019). Zhibin Jiang et al., “High-power Si-Ge photodiode assisted by doping regulation,” Optics Express 29, 7389 (2021). Xiao Hu et al. al., “High-speed and high-power germanium photodetector with a lateral silicon nitride waveguide,” Photonics Research 9, 749 (2021).

[0006] The method described in Non-Patent Document 1 requires an increased number of photodiodes and has low integration, while the methods described in Non-Patent Documents 2 and 3 require special techniques and lack versatility.

[0007] The present invention has been made in view of the above problems, and has an object to provide a high-output photoelectric conversion element.

[0008] In order to solve the above problems, the present invention provides the following means.

[0009] A photoelectric conversion element according to a first aspect includes a first stacked body and a first optical waveguide. The first stacked body includes a first impurity semiconductor arranged at an upper portion in a stacking direction, a second impurity semiconductor having a conductivity type different from that of the first impurity semiconductor and arranged at an upper portion in the stacking direction, and a first intrinsic semiconductor sandwiched between the first impurity semiconductor and the second impurity semiconductor in the stacking direction. The first intrinsic semiconductor of the first stacked body has a first side longer than a second side intersecting with the first side when viewed from the stacking direction. The first optical waveguide is connected to a first side surface to which the first side of the first stacked body belongs.

[0010] The photoelectric conversion element according to this embodiment is less susceptible to saturation and has high output.

[0011] FIG. 1 is a plan view of a photoelectric conversion element according to the first embodiment. FIG. 2 is a cross-sectional view of a photoelectric conversion element according to the first embodiment. FIG. 3 is a plan view of a photoelectric conversion element according to the second embodiment. FIG. 4 is a cross-sectional view of a photoelectric conversion element according to the third embodiment. FIG. 5 is a plan view of another example of a photoelectric conversion element according to the third embodiment. FIG. 6 is a plan view of a photoelectric conversion element according to the fourth embodiment. FIG. 7 is a cross-sectional view of a photoelectric conversion element according to the fifth embodiment. FIG. 8 is a cross-sectional view of a photoelectric conversion element according to the sixth embodiment. FIG. 9 is a cross-sectional view of a photoelectric conversion element according to the seventh embodiment. FIG. 10 is a cross-sectional view of a photoelectric conversion element according to the seventh embodiment. FIG. 11 shows output characteristics of a photoelectric conversion element according to Example 1. FIG. 12 is a plan view of a photoelectric conversion element according to Comparative Example 1. FIG. 13 is a cross-sectional view of a photoelectric conversion element according to Comparative Example 1. FIG. 14 shows output characteristics of a photoelectric conversion element according to Comparative Example 1.

[0012] The present embodiment will be described in detail below. The following description is an example of the present invention, and the present invention is not limited thereto, and can be implemented with appropriate modifications within the scope of the present invention.

[0013] First, the directions will be defined. The direction in which the first laminate is stacked is defined as the Z direction. The first direction perpendicular to the Z direction is defined as the X direction. The direction perpendicular to the Z direction and the X direction is defined as the Y direction. In this specification, the +Z direction may be expressed as "up" and the -Z direction as "down", but these expressions are used for convenience and do not define the direction of gravity.

[0014] "First embodiment" Fig. 1 is a plan view of a photoelectric conversion element 100 according to the first embodiment. Fig. 2 is a cross-sectional view of the photoelectric conversion element 100 according to the first embodiment. Fig. 2 is an xz cross-sectional view passing through the first stack 10. The photoelectric conversion element 100 is a light-receiving element that receives light and generates electrical energy. The photoelectric conversion element 100 is a waveguide-type light-receiving element.

[0015] The photoelectric conversion element 100 according to the first embodiment has a first laminate 10, a first optical waveguide 20, a protective layer 30, a first electrode E1, and a second electrode E2.

[0016] The shape of the first stacked body 10 when viewed from the Z direction is, for example, rectangular. The shape of the first stacked body 10 when viewed from the Z direction is not limited to this example as long as it has long sides and short sides.

[0017] The first stacked body 10 includes a first impurity semiconductor 11, a second impurity semiconductor 12, and a first intrinsic semiconductor 13. The first impurity semiconductor 11 and the second impurity semiconductor 12 sandwich the first intrinsic semiconductor 13 in the Z direction. The first impurity semiconductor 11 is located at the top of the first stacked body 10 in the Z direction, and the second impurity semiconductor 12 is located at the bottom of the first stacked body 10 in the Z direction. The first impurity semiconductor 11 and the second impurity semiconductor 12 have different conductivity types. For example, the first impurity semiconductor 11 may be an n-type semiconductor and the second impurity semiconductor 12 may be a p-type semiconductor, or the first impurity semiconductor 11 may be a p-type semiconductor and the second impurity semiconductor 12 may be an n-type semiconductor. The first stacked body 10 is a PIN photodiode.

[0018] The first impurity semiconductor 11 is in contact with the first intrinsic semiconductor 13. The first impurity semiconductor 11 is located above the first intrinsic semiconductor 13 in the Z direction. The first impurity semiconductor 11 is obtained, for example, by injecting a dopant into a part of the first intrinsic semiconductor 13. The first impurity semiconductor 11 is, for example, an n-type semiconductor. The first impurity semiconductor 11 is, for example, germanium doped with nitrogen, phosphorus, arsenic, or antimony.

[0019] The first impurity semiconductor 11 is not limited to the example shown in FIG. 2 . For example, the first impurity semiconductor 11 may be formed on a semiconductor cap layer formed on the first intrinsic semiconductor 13. The cap layer is, for example, silicon, SiGe, or the like. The first impurity semiconductor 11 is formed by adding a dopant to a part of the cap layer. The first impurity semiconductor 11 may be, for example, silicon or SiGe doped with any of nitrogen, phosphorus, arsenic, and antimony.

[0020] The second impurity semiconductor 12 is in contact with the first intrinsic semiconductor 13. The second impurity semiconductor 12 is located below the first intrinsic semiconductor 13 in the Z direction. The second impurity semiconductor 12 has a conductivity type different from that of the first impurity semiconductor 11. The second impurity semiconductor 12 is, for example, a p-type semiconductor. The second impurity semiconductor 12 is, for example, silicon doped with boron, aluminum, gallium, or indium. The second impurity semiconductor 12 may have a low-concentration region 12A and a high-concentration region 12B. The low-concentration region 12A has a lower impurity concentration than the high-concentration region 12B. The low-concentration region 12A may have, for example, a p-type semiconductor. ＋ The high concentration region 12B is a semiconductor, for example, p ＋＋ It is a semiconductor.

[0021] The first intrinsic semiconductor 13 is sandwiched between the first impurity semiconductor 11 and the second impurity semiconductor 12. The first intrinsic semiconductor 13 is also called an i-type semiconductor. The first intrinsic semiconductor 13 is, for example, germanium. The first impurity semiconductor 11 and the first intrinsic semiconductor 13 may be compound semiconductors.

[0022] When viewed from the Z direction, the first intrinsic semiconductor 13 has, for example, a first side S1 and a second side S2. The second side S2 intersects with the first side S1. The first side S1 is, for example, a long side of the rectangular first intrinsic semiconductor 13. The second side S2 is, for example, a short side of the rectangular first intrinsic semiconductor 13. The length of the first side S1 is longer than the length of the second side S2.

[0023] The length of the first side S1 relative to the length of the second side S2 is defined as the aspect ratio. The aspect ratio of the first intrinsic semiconductor 13 is preferably 5 or greater, more preferably 10 or greater, and even more preferably 20 or greater. If the aspect ratio of the first intrinsic semiconductor 13 is large, the light-receiving area can be increased even if the first intrinsic semiconductor 13 has a small area.

[0024] The length of the first side S1 is preferably 25 μm or more, more preferably 50 μm or more, even more preferably 100 μm or more, and even more preferably 200 μm or more. The longer the length of the first side S1, the wider the light receiving surface of the first stack 10. The length of the first side S1 may be 1000 μm or less.

[0025] The length of the second side S2 is preferably 20 μm or less, more preferably 10 μm or less, and even more preferably 8 μm or less. The length of the second side S2 may be 1 μm or more.

[0026] The thickness of the first intrinsic semiconductor 13 in the Z direction is, for example, 100 nm to 5 μm, preferably 200 nm to 2 μm, and more preferably 400 nm to 1 μm.

[0027] The first optical waveguide 20 is a path for light to propagate to the first laminate 10. The first optical waveguide 20 is connected to a first side surface to which the first edge S1 of the first laminate 10 belongs. When light is irradiated onto the first side surface of the first laminate 10, the direction in which the first laminate 10 absorbs light and the direction in which carriers travel within the first laminate 10 are perpendicular to each other, and the light receiving sensitivity and response speed of the photoelectric conversion element 100 can be individually designed.

[0028] The first optical waveguide 20 may be connected to, for example, the second impurity semiconductor 12 of the first stack 10, or may be connected to the first intrinsic semiconductor 13. Even when the first optical waveguide 20 is connected to the second impurity semiconductor 12 of the first stack 10, light can propagate to the first intrinsic semiconductor 13 via the second impurity semiconductor 12.

[0029] The first optical waveguide 20 includes, for example, an optical waveguide section 20 A and a light irradiation section 20 B. The light irradiation section 20 B connects a first end of the optical waveguide section 20 A and a first side surface of the first laminate 10 .

[0030] The material forming the optical waveguide 20A may be silicon or a material other than silicon. Examples of the material forming the optical waveguide 20A other than silicon include SiN, SiON, and SiO ｘ , amorphous silicon. The optical waveguide 20A has a narrow linewidth and often propagates high-energy light. Even when propagating high-energy light, the optical waveguide 20A preferably includes SiN, which has smaller absorption loss than silicon.

[0031] The material constituting the light irradiating portion 20B is preferably silicon. The light irradiating portion 20B may be formed in the same layer as the second impurity semiconductor 12. If the light irradiating portion 20B is silicon, processing such as forming the second impurity semiconductor 12 becomes easier.

[0032] The width of the light irradiation unit 20B in the Y direction increases as it approaches the first laminate 10. The light that reaches the light irradiation unit 20B is spread by the light irradiation unit 20B and reaches the first side surface of the first laminate 10. By spreading the light by the light irradiation unit 20B, it is possible to prevent the light from being irradiated only at a predetermined position on the first laminate 10, and it is possible to suppress saturation of the output from the first laminate 10.

[0033] The relationship between the optical waveguide 20A and the light irradiation unit 20B shown in Fig. 1 is an example, and this relationship is not limited to this example. For example, at the connection position between the optical waveguide 20A and the light irradiation unit 20B, the widths of the respective units may be continuously connected as shown in Fig. 1, or may be discontinuously connected. When the widths of the optical waveguide 20A and the light irradiation unit 20B are discontinuously connected, the width of the optical waveguide 20A and the width of the light irradiation unit 20B differ at the connection interface between the optical waveguide 20A and the light irradiation unit 20B.

[0034] 1 is also an example and is not limited to this example. For example, the width of the light irradiation unit 20B in the Y direction may become narrower as it approaches the first stack 10, or the width in the Y direction may remain constant.

[0035] The first electrode E1 is connected to the first impurity semiconductor 11. The second electrode E2 is connected to the second impurity semiconductor 12. The first electrode E1 and the second electrode E2 are terminals for outputting the power generated by photoelectric conversion to the outside. The photoelectric conversion element 100 according to the first embodiment is a two-terminal element. There is no particular restriction on the first electrode E1 and the second electrode E2 as long as they are conductive.

[0036] The protective layer 30 covers the first stacked body 10 and the first optical waveguide 20. The protective layer 30 protects the first stacked body 10 and the first optical waveguide 20 from external factors. The protective layer 30 is, for example, silicon oxide.

[0037] The photoelectric conversion element 100 according to this embodiment can be fabricated using a general semiconductor process. Each layer can be formed using a chemical vapor deposition (CVD) method, a sputtering method, a vapor deposition method, or the like. Impurities can be implanted into the semiconductor by, for example, an ion implantation method, an in situ doping method, a thermal diffusion method, or the like. Each member can be processed using, for example, a photolithography method, an electron beam lithography method, or the like.

[0038] The photoelectric conversion element 100 according to this embodiment converts light into electricity. Light propagating through the first optical waveguide 20 is irradiated onto the first stacked body 10. When light is irradiated onto the PIN junction of the first stacked body 10, electrons and holes are generated. The generated electrons and holes move to the first electrode E1 and the second electrode E2, respectively, thereby generating a photocurrent.

[0039] In the photoelectric conversion element 100 according to this embodiment, the first optical waveguide 20 is connected to the long side of the first stack 10. The photoelectric conversion element 100 according to this embodiment has a wide light-receiving surface and absorbs light over a wide area, so that the saturation phenomenon in which the output (photocurrent) is saturated is unlikely to occur. In other words, the photoelectric conversion element 100 according to this embodiment can achieve high output.

[0040] 3 is a plan view of a photoelectric conversion element 101 according to a second embodiment. The photoelectric conversion element 101 according to the second embodiment has a first stacked body 10, a first optical waveguide 21, a protective layer 30, a first electrode E1, and a second electrode E2.

[0041] The photoelectric conversion element 101 according to the second embodiment differs from the photoelectric conversion element 100 according to the first embodiment in the shape of the first optical waveguide 21. In the photoelectric conversion element 101 according to the second embodiment, the same components as those in the photoelectric conversion element 100 according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0042] The first optical waveguide 21 is a path through which light propagates to the first laminate 10. The first optical waveguide 21 is connected to a first side surface to which the first edge S1 of the first laminate 10 belongs. The first optical waveguide 21 may be connected to, for example, the second impurity semiconductor 12 or the first intrinsic semiconductor 13 of the first laminate 10.

[0043] The first optical waveguide 21 is connected obliquely to the first side surface of the first laminate 10. The incident direction of light from the first optical waveguide 21 to the first laminate 10 is oblique to the first side surface. The incident direction of light from the first optical waveguide 21 to the first laminate 10 is inclined with respect to, for example, the X direction and the Y direction.

[0044] The first optical waveguide 21 may have an optical waveguide section 21 A and a light irradiation section 21 B. The optical waveguide section 21 A is similar to the optical waveguide section 20 A. The light irradiation section 21 B is similar to the light irradiation section 20 B.

[0045] The photoelectric conversion element 101 according to the second embodiment has the same effects as the photoelectric conversion element 100 according to the first embodiment. Furthermore, the photoelectric conversion element 101 according to the second embodiment can suppress the generation of returned light because light is irradiated from an oblique direction onto the first side surface of the first laminate 10. Returned light is light that is generated when a portion of the light irradiated from the first optical waveguide 21 onto the first laminate 10 is reflected and returns to the first optical waveguide 21. Returned light reduces the performance of the light source.

[0046] 4 is a plan view of a photoelectric conversion element 102 according to a third embodiment. The photoelectric conversion element 102 according to the third embodiment has a first stacked body 10, a first optical waveguide 22, a protective layer 30, a first electrode E1, and a second electrode E2.

[0047] The photoelectric conversion element 102 according to the third embodiment is different from the photoelectric conversion element 100 according to the first embodiment in the shape of the first optical waveguide 22. In the photoelectric conversion element 102 according to the third embodiment, the same components as those in the photoelectric conversion element 100 according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0048] The first optical waveguide 22 is a path through which light propagates to the first laminate 10. The first optical waveguide 22 is connected to a first side surface to which the first edge S1 of the first laminate 10 belongs. The first optical waveguide 22 may be connected to, for example, the second impurity semiconductor 12 or the first intrinsic semiconductor 13 of the first laminate 10.

[0049] The first optical waveguide 22 has an optical waveguide section 22A, one or more optical branching sections 22C, and a plurality of light emitting sections 22B. The optical waveguide section 22A is similar to the optical waveguide section 20A.

[0050] The optical branching section 22C branches a part of the light propagating through the optical waveguide section 22A and distributes the light to each of the plurality of light emitting sections 22B. The optical branching section 22C is, for example, a directional coupler.

[0051] Each of the plurality of light irradiating sections 22B is similar to the light irradiating section 20B. By dividing the light into the plurality of light irradiating sections 22B, the light can be uniformly incident on the first stacked body 10.

[0052] The photoelectric conversion element 102 according to the third embodiment has the same effects as the photoelectric conversion element 100 according to the first embodiment. Furthermore, the photoelectric conversion element 102 according to the third embodiment can increase the homogeneity of the light incident on the first stack 10 by dividing the light, and therefore can further prevent the output from saturating.

[0053] Furthermore, the optical branching structure is not limited to the structure shown in Fig. 4. For example, Fig. 5 is a plan view of another example of a photoelectric conversion element 102A according to the third embodiment. The photoelectric conversion element 102A uses a first optical waveguide 22' instead of the first optical waveguide 22 of the photoelectric conversion element 102. The first optical waveguide 22' has an optical waveguide section 22A', one or more optical branching sections 22C', and a plurality of light irradiation sections 22B'. The photoelectric conversion element 102A has a tree-shaped optical branching structure.

[0054] Alternatively, the optical branching structure may be a multi-port MMI (Multi-Mode Interference), a multi-port directional coupler, or a 1×N star coupler.

[0055] 6 is a plan view of a photoelectric conversion element 103 according to a fourth embodiment. The photoelectric conversion element 103 according to the fourth embodiment has a first stacked body 10, a first optical waveguide 23, a protective layer 30, a first electrode E1, and a second electrode E2.

[0056] The photoelectric conversion element 103 according to the fourth embodiment differs from the photoelectric conversion element 100 according to the first embodiment in the shape of the first optical waveguide 23. In the photoelectric conversion element 103 according to the fourth embodiment, the same components as those in the photoelectric conversion element 100 according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0057] The first optical waveguide 23 is a path for propagating light to the first laminate 10. The first optical waveguide 23 is connected to a first side surface to which the first edge S1 of the first laminate 10 belongs. The first optical waveguide 23 may be connected to, for example, the second impurity semiconductor 12 or the first intrinsic semiconductor 13 of the first laminate 10.

[0058] The first optical waveguide 23 has a plurality of optical waveguide sections 23A and a light irradiation section 23B. Each of the optical waveguide sections 23A is similar to the optical waveguide section 20A. The light irradiation section 23B is similar to the light irradiation section 20B. There are a plurality of optical waveguide sections 23A, which are branched before reaching the light irradiation section 23B. Light incident from each of the optical waveguide sections 23A interferes at the light irradiation section 23B and reaches the first stack 10.

[0059] The photoelectric conversion element 103 according to the fourth embodiment has the same effects as the photoelectric conversion element 100 according to the first embodiment.

[0060] 7 is a plan view of a photoelectric conversion element 104 according to a fifth embodiment. The photoelectric conversion element 104 according to the fifth embodiment has a first stacked body 10, a first optical waveguide 20, a protective layer 30, a first electrode E1, a second electrode E2, a third electrode E3, a first resistor element 41, and a second resistor element 42.

[0061] The photoelectric conversion element 104 according to the fifth embodiment differs from the photoelectric conversion element 100 according to the first embodiment in that it has a third electrode E3, a first resistor element 41, and a second resistor element 42. In the photoelectric conversion element 104 according to the fifth embodiment, the same components as those in the photoelectric conversion element 100 according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0062] The third electrode E3 is electrically parallel to the first electrode E1. The third electrode E3 is connected to the first impurity semiconductor 11. The first electrode E1, the second electrode E2, and the third electrode E3 are terminals for outputting the power generated by photoelectric conversion to the outside. The photoelectric conversion element 104 according to the fifth embodiment is a three-terminal element. The third electrode E3 may be any electrode as long as it is conductive.

[0063] The first resistor element 41 is located between the first stack 10 and the third electrode E3. The second resistor element 42 is located between the first stack 10 and the first electrode E1.

[0064] The resistance value of the first resistor element 41 is greater than the combined resistance of the third electrode E3 and the wiring connected thereto. The resistance value of the second resistor element 42 is greater than the combined resistance of the first electrode E1 and the wiring connected thereto. The resistance values ​​of the first resistor element 41 and the second resistor element 42 are approximately equal.

[0065] The photoelectric conversion element 104 according to the fifth embodiment has the same effects as the photoelectric conversion element 100 according to the first embodiment. The photoelectric conversion element 104 according to the fifth embodiment is a three-terminal element, and the first resistor element 41 and the second resistor element 42 can make the amount of current flowing through the first electrode E1 and the third electrode E3 approximately equal, thereby reducing high-frequency loss of the electrical signal. Note that if the amount of current flowing through the first electrode E1 and the third electrode E3 can be made approximately equal without the first resistor element 41 and the second resistor element 42, the first resistor element 41 and the second resistor element 42 may be omitted.

[0066] Sixth Embodiment Fig. 8 is a cross-sectional view of a photoelectric conversion element 105 according to a sixth embodiment. Fig. 8 is an xz cross-sectional view passing through a first stacked body 10'. The photoelectric conversion element 105 according to the sixth embodiment has a first stacked body 10', a first optical waveguide 20, a protective layer 30, a first electrode E1, and a second electrode E2.

[0067] The photoelectric conversion element 105 according to the sixth embodiment differs from the photoelectric conversion element 100 according to the first embodiment in the shape of the first intrinsic semiconductor 13′ of the first stack 10′. In the photoelectric conversion element 105 according to the sixth embodiment, the same components as those in the photoelectric conversion element 100 according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0068] A bottom surface B1 of the first intrinsic semiconductor 13' is located below a top surface A1 of the first optical waveguide 20 at the connection point with the first side surface. In the Z direction, a part of the first intrinsic semiconductor 13' is located at the same height as the light irradiated portion 20B of the first optical waveguide 20. A part of the second impurity semiconductor 12 is recessed downward at a position overlapping with the first intrinsic semiconductor 13'.

[0069] The photoelectric conversion element 105 according to the sixth embodiment has the same effects as the photoelectric conversion element 100 according to the first embodiment. Furthermore, the photoelectric conversion element 105 according to the sixth embodiment directly inputs light that has propagated through the first optical waveguide 20 into the first intrinsic semiconductor 13′, thereby shortening the absorption length of the light.

[0070] Seventh Embodiment Fig. 9 is a plan view of a photoelectric conversion element 106 according to a seventh embodiment. Fig. 10 is a cross-sectional view of the photoelectric conversion element 106 according to the seventh embodiment. Fig. 10 is an xz cross-sectional view passing through the first stacked body 10. The photoelectric conversion element 106 according to the seventh embodiment has a first stacked body 10, a first optical waveguide 20, a protective layer 30, a second stacked body 50, a second optical waveguide 60, a fourth electrode E4, a fifth electrode E5, and a sixth electrode E6.

[0071] The photoelectric conversion element 106 according to the seventh embodiment differs from the photoelectric conversion element 100 according to the first embodiment in that it has a second stacked body 50 and a second optical waveguide 60, and has a fourth electrode E4, a fifth electrode E5, and a sixth electrode E6 instead of the first electrode E1 and the second electrode E2. In the photoelectric conversion element 106 according to the seventh embodiment, the same components as those in the photoelectric conversion element 100 according to the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

[0072] The shape of the second stack 50 when viewed from the Z direction is, for example, rectangular. The shape of the second stack 50 when viewed from the Z direction is not limited to this example as long as it has long sides and short sides.

[0073] The second stack 50 includes a third impurity semiconductor 51, a fourth impurity semiconductor 52, and a second intrinsic semiconductor 53. The third impurity semiconductor 51 and the fourth impurity semiconductor 52 sandwich the second intrinsic semiconductor 53 in the Z direction. The third impurity semiconductor 51 is located at the top of the second stack 50 in the Z direction, and the fourth impurity semiconductor 52 is located at the bottom of the second stack 50 in the Z direction. The third impurity semiconductor 51 and the fourth impurity semiconductor 52 have different conductivity types. The third impurity semiconductor 51 has the same conductivity type as the first impurity semiconductor 11 of the first stack 10. The fourth impurity semiconductor 52 has the same conductivity type as the second impurity semiconductor 12 of the first stack 10. The second stack 50 is a PIN type photodiode.

[0074] The third impurity semiconductor 51 is in contact with the second intrinsic semiconductor 53. The third impurity semiconductor 51 is located on top of the second intrinsic semiconductor 53. The third impurity semiconductor 51 is obtained, for example, by injecting a dopant into a part of the second intrinsic semiconductor 53. The third impurity semiconductor 51 is, for example, an n-type semiconductor. The third impurity semiconductor 51 is, for example, germanium doped with nitrogen, phosphorus, arsenic, or antimony. The third impurity semiconductor 51 may be formed in a cap layer, similar to the first impurity semiconductor 11.

[0075] The fourth impurity semiconductor 52 is in contact with the second intrinsic semiconductor 53. The fourth impurity semiconductor 52 is located below the second intrinsic semiconductor 53 in the Z direction. The fourth impurity semiconductor 52 is, for example, a p-type semiconductor. The fourth impurity semiconductor 52 is, for example, silicon doped with boron, aluminum, gallium, or indium. The fourth impurity semiconductor 52 may have a low-concentration region 52A and a high-concentration region 52B. The low-concentration region 52A has a lower impurity concentration than the high-concentration region 52B. The low-concentration region 52A is, for example, a p-type semiconductor. ＋ The high concentration region 52B is a semiconductor, for example, p ＋＋ The high concentration region 52B may be a semiconductor.

[0076] The second intrinsic semiconductor 53 is sandwiched between the third impurity semiconductor 51 and the fourth impurity semiconductor 52. The second intrinsic semiconductor 53 is also called an i-type semiconductor. The second intrinsic semiconductor 53 is, for example, germanium. The third impurity semiconductor 51 and the second intrinsic semiconductor 53 may be compound semiconductors.

[0077] When viewed from the Z direction, the second intrinsic semiconductor 53 has, for example, a third side S3 and a fourth side S4. The fourth side S4 intersects with the third side S3. The third side S3 is, for example, a long side of the rectangular second intrinsic semiconductor 53. The fourth side S4 is, for example, a short side of the rectangular second intrinsic semiconductor 53. The length of the third side S3 is longer than the length of the fourth side S4.

[0078] The aspect ratio between the third side S3 and the fourth side S4 (the length of the third side S3 relative to the length of the fourth side S4) is equal to the aspect ratio between the first side S1 and the second side S2. The length of the third side S3 is equal to the length of the first side S1. The length of the fourth side S4 is equal to the length of the second side S2. It is preferable that the shapes of the first stack 10 and the second stack 50 are approximately equal.

[0079] The second optical waveguide 60 is a path for propagating light to the second laminate 50. The second optical waveguide 60 is connected to the second side surface to which the third side S3 of the second laminate 50 belongs. The first optical waveguide 20 and the second optical waveguide 60 are branched from the same optical waveguide, and light of approximately the same intensity propagates through them.

[0080] The second optical waveguide 60 may be connected to, for example, the fourth impurity semiconductor 52 of the second stacked body 50, or may be connected to the second intrinsic semiconductor 53. Even when the second optical waveguide 60 is connected to the fourth impurity semiconductor 52 of the second stacked body 50, light can propagate to the second intrinsic semiconductor 53 via the fourth impurity semiconductor 52.

[0081] The second optical waveguide 60 has, for example, an optical waveguide portion 60A and a light irradiation portion 60B. The light irradiation portion 60B connects a first end of the optical waveguide portion 60A and a second side surface of the second laminate 50. The second optical waveguide 60 has a configuration similar to that of the first optical waveguide 20. The second optical waveguide 60 can have the same modified examples as the first optical waveguide 20.

[0082] The fourth electrode E4 is connected to the first impurity semiconductor 11 of the first stack 10. The fifth electrode E5 is connected to the third impurity semiconductor 51 of the second stack 50. The sixth electrode E6 is connected to the second impurity semiconductor 12 of the first stack 10 and the fourth impurity semiconductor 52 of the second stack 50. The fourth electrode E4, the fifth electrode E5, and the sixth electrode E6 are terminals for outputting power generated by photoelectric conversion to the outside. The photoelectric conversion element 106 according to the seventh embodiment is a three-terminal element. The fourth electrode E4, the fifth electrode E5, and the sixth electrode E6 may be any electrode as long as they are conductive. The fourth electrode E4 is electrically parallel to the fifth electrode E5.

[0083] The photoelectric conversion element 106 according to the seventh embodiment has the same effects as the photoelectric conversion element 100 according to the first embodiment. The photoelectric conversion element 106 according to the seventh embodiment is a three-terminal element, and the amount of current flowing through the fourth electrode E4 and the fifth electrode E5 can be made approximately equal, thereby reducing high-frequency loss in the electrical signal. Furthermore, in the photoelectric conversion element 106 according to the seventh embodiment, the first stacked body 10 and the second stacked body 50 each perform photoelectric conversion, so that a saturated output that is twice that of the photoelectric conversion element 100 can be obtained.

[0084] Although the preferred embodiments of the present invention have been described in detail above, the present invention is not limited to the specific embodiments, and various modifications and changes are possible within the scope of the gist of the present invention as set forth in the claims.

[0085] Example 1 In Example 1, the photoelectric conversion element 100 shown in FIG. 1 was fabricated. The length of the first side S1 of the first stack 10 was 200 μm, and the length of the second side S2 was 8 μm. Light having a wavelength of 1550 nm was irradiated onto the first intrinsic semiconductor 13 made of germanium. FIG. 11 shows the output characteristics of the photoelectric conversion element 100 according to Example 1. The horizontal axis of FIG. 11 represents the intensity of light irradiated onto the first intrinsic semiconductor 13, and the vertical axis represents the photocurrent flowing between the first electrode E1 and the second electrode E2.

[0086] 11 , in the photoelectric conversion element 100 of Example 1, the output (photocurrent flowing between the first electrode E1 and the second electrode E2) increased linearly as the intensity of light irradiated on the first intrinsic semiconductor 13 increased. The output from the photoelectric conversion element 100 of Example 1 did not saturate even when the output exceeded 20 mA, and increased linearly. The photoelectric conversion efficiency of the photoelectric conversion element 100 of Example 1 was 0.93 A / W.

[0087] Comparative Example 1 In Comparative Example 1, a photoelectric conversion element 110 shown in Fig. 12 was fabricated. Fig. 12 is a plan view of the photoelectric conversion element 110 according to Comparative Example 1. Fig. 13 is a cross-sectional view of the photoelectric conversion element 110 according to Comparative Example 1.

[0088] The photoelectric conversion element 110 according to Comparative Example 1 has a first stacked body 10, a first optical waveguide 20, a protective layer 30, a first electrode E1, a second electrode E2, and a seventh electrode E7. The photoelectric conversion element 110 according to Comparative Example 1 differs from the photoelectric conversion element 100 according to the first embodiment in that the connection point between the first stacked body 10 and the first optical waveguide 20 is different and that the photoelectric conversion element 110 according to Comparative Example 1 has a seventh electrode E7. In the photoelectric conversion element 110 according to Comparative Example 1, the same components as those in the photoelectric conversion element 100 according to the first embodiment are denoted by the same reference numerals.

[0089] The photoelectric conversion element 110 according to Comparative Example 1 is a three-terminal element. The seventh electrode E7 is electrically parallel to the second electrode E2. The seventh electrode E7 is connected to the second impurity semiconductor 12 of the first stacked body 10. The first optical waveguide 20 is connected to the second side S2 of the first stacked body 10. The length of the second side S2 is 8 μm. The length of the first side S1 is 100 μm. The length of the second side S2 is shorter than the length of the first side S1.

[0090] Light having a wavelength of 1550 nm was irradiated onto the first intrinsic semiconductor 13 made of germanium of the photoelectric conversion element 110 according to Comparative Example 1. Fig. 14 shows the output characteristics of the photoelectric conversion element 110 according to Comparative Example 1. The horizontal axis of Fig. 14 represents the intensity of light irradiated onto the first intrinsic semiconductor 13, and the vertical axis represents the photocurrent flowing between the first electrode E1 and the second electrode E2 and the seventh electrode E7.

[0091] 14 , in the photoelectric conversion element 110 of Comparative Example 1, the output (photocurrent flowing between the first electrode E1, the second electrode E2, and the seventh electrode E7) increased as the intensity of light irradiated on the first intrinsic semiconductor 13 increased. On the other hand, the output of the photoelectric conversion element 110 of Comparative Example 1 saturated at about 10 mA. The photoelectric conversion efficiency of the photoelectric conversion element 100 of Comparative Example 1 was 0.92 A / W when the output was below 10 mA, but gradually decreased due to output saturation when the output exceeded 10 mA, and was about 0.6 A / W at a light intensity of 20 mW.

[0092] As can be seen from a comparison of the results of Example 1 and Comparative Example 1, the photoelectric conversion element 100 according to Example 1 is less likely to saturate in output and can achieve high output.

[0093] The photoelectric conversion element according to the present disclosure has a high output power and is resistant to output saturation. The photoelectric conversion element according to the present disclosure can be incorporated into a silicon photonics circuit. The photoelectric conversion element according to the present disclosure can also be used as an output source of radio waves (e.g., microwaves) and a driving source for devices (e.g., optical modulators, spintronics devices).

[0094] 10, 10' First stacked body 11 First impurity semiconductor 12 Second impurity semiconductor 12A, 52A Low concentration region 12B, 52B High concentration region 13, 13' First intrinsic semiconductor 20, 21, 22, 22', 23 First optical waveguide 20A, 21A, 22A, 22A', 23A, 60A Optical waveguide section 20B, 21B, 22B, 22B', 23B, 60B Light irradiation section 22C, 22C' Optical branching section 30 Protective layer 41 First resistor element 42 Second resistor element 50 Second stacked body 51 Third impurity semiconductor 52 Fourth impurity semiconductor 53 Second intrinsic semiconductor 60 Second optical waveguide 100, 101, 102, 102A, 103, 104, 105, 106, 110 Photoelectric conversion element A1 Top surface B1 Bottom surface E1 First electrode E2 Second electrode E3 Third electrode E4 Fourth electrode E5 Fifth electrode E6 Sixth electrode E7 Seventh electrode S1 First side S2 Second side S3 Third side S4 4th side

Claims

1. A photoelectric conversion element comprising a first stack and a first optical waveguide, wherein the first stack has a first impurity semiconductor arranged at an upper portion in a stacking direction, a second impurity semiconductor having a conductivity type different from that of the first impurity semiconductor and arranged at a lower portion in the stacking direction, and a first intrinsic semiconductor sandwiched between the first impurity semiconductor and the second impurity semiconductor in the stacking direction, wherein the first intrinsic semiconductor of the first stack has a first side length longer than a second side length intersecting with the first side length when viewed from the stacking direction, and the first optical waveguide is connected to a first side surface to which the first side of the first stack belongs.

2. The photoelectric conversion element according to claim 1, wherein the aspect ratio, which is the ratio of the length of the first side to the length of the second side, is 5 or more.

3. The photoelectric conversion element according to claim 1, wherein the length of the first side is 25 μm or more.

4. The photoelectric conversion element according to claim 1, wherein the first optical waveguide has a light irradiation portion, and the light irradiation portion has a width that increases as it approaches the first laminate.

5. The photoelectric conversion element according to claim 1, wherein the first optical waveguide is connected obliquely to the first side surface of the first laminate.

6. The photoelectric conversion element according to claim 1, wherein the first optical waveguide has a plurality of light irradiation portions, and light propagating through the first optical waveguide is branched and incident on the first side surface from each of the plurality of light irradiation portions.

7. The photoelectric conversion element according to claim 1, wherein the first optical waveguide has a light irradiation section, and the light propagating through the first optical waveguide is branched before reaching the light irradiation section.

8. The photoelectric conversion element according to claim 1, further comprising: a first electrode connected to the first impurity semiconductor of the first stack; and a second electrode connected to the second impurity semiconductor of the first stack.

9. The photoelectric conversion element according to claim 8, further comprising a third electrode that is electrically parallel to the first electrode with respect to the first stacked body.

10. The photoelectric conversion element according to claim 9, further comprising a first resistor element and a second resistor element, wherein the first resistor element is located between the first stack and the third electrode, and the second resistor element is located between the first stack and the first electrode that is in a parallel relationship with the third electrode.

11. The photoelectric conversion element according to claim 1, wherein the bottom surface of the first intrinsic semiconductor is located below the top surface of the first optical waveguide at the connection point with the first side surface.

12. The semiconductor device further comprises a second stack, a second optical waveguide, a fourth electrode, a fifth electrode, and a sixth electrode, wherein the second stack has a third impurity semiconductor disposed at an upper portion in the stacking direction, a fourth impurity semiconductor having a conductivity type different from that of the third impurity semiconductor and disposed at a lower portion in the stacking direction, and a second intrinsic semiconductor sandwiched between the third impurity semiconductor and the fourth impurity semiconductor in the stacking direction, wherein the third impurity semiconductor has the same conductivity type as the first impurity semiconductor, and the fourth impurity semiconductor has the same conductivity type as the second impurity semiconductor, wherein the second intrinsic semiconductor of the second stack has a third side longer than a fourth side intersecting with the third side when viewed from the stacking direction, wherein the second optical waveguide is connected to a second side surface to which the third side of the second stack belongs, wherein the first optical waveguide and the second optical waveguide are branched from the same optical waveguide, and wherein the fourth electrode is connected to the first impurity semiconductor of the first stack, 2. The photoelectric conversion element according to claim 1, wherein the fifth electrode is connected to the third impurity semiconductor of the second stack, and the sixth electrode is connected to the second impurity semiconductor of the first stack and the fourth impurity semiconductor of the second stack.

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