Semiconductor light receiving element

Abstract

The present invention relates to a semiconductor light receiving element. A semiconductor light receiving element comprises a first semiconductor layer, a waveguide photodiode structure, an optical waveguide structure and a fourth semiconductor layer. The waveguide photodiode structure is arranged on the first semiconductor layer. The waveguide photodiode structure comprises a light absorption layer, a second semiconductor layer, a multiplication layer and a third semiconductor layer. The optical waveguide structure is arranged on the first semiconductor layer. The optical waveguide structure comprises an optical waveguide core layer and a cladding layer. The end face of the waveguide photodiode structure faces the end face of the optical waveguide structure. The fourth semiconductor layer is located between the end face of the waveguide photodiode structure and the end face of the optical waveguide structure. The fourth semiconductor layer is in contact with the multiplication layer at the end face of the waveguide photodiode structure.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based upon and claims the benefit of priority from Japanese patent application No. 2020-035037, filed on March 2, 2020, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a semiconductor light receiving element. Background Art

[0004] JP2013-110207A discloses a technology related to a semiconductor optical integrated component and a method for manufacturing the same. The semiconductor optical integrated component includes a photodiode region formed on a semiconductor substrate, and an optical waveguide region including a butt joint coupled to an end face of the photodiode region. The photodiode region includes a light absorption layer and a p-type cladding layer sequentially stacked on an n-type cladding layer. The optical waveguide region includes an optical waveguide layer and an upper cladding layer sequentially stacked on the n-type cladding layer. The optical waveguide layer has a rising portion relative to the inclined butt joint end face. Summary of the invention

[0005] The present disclosure provides a semiconductor light receiving element. The semiconductor light receiving element includes a first semiconductor layer, a waveguide photodiode structure, an optical waveguide structure and a fourth semiconductor layer. The first semiconductor layer is of a first conductivity type. The waveguide photodiode structure has an end face arranged on the first semiconductor layer. The waveguide photodiode structure includes a light absorption layer, a second semiconductor layer, a multiplication layer and a third semiconductor layer. The light absorption layer is of an intrinsic conductivity type or a first conductivity type. The second semiconductor layer is of a first conductivity type. The multiplication layer is of an intrinsic conductivity type or a first conductivity type. The third semiconductor layer is of a second conductivity type. The optical waveguide structure has an end face arranged on the first semiconductor layer. The optical waveguide structure includes an optical waveguide core layer and a cladding layer. The end face of the waveguide photodiode structure faces the end face of the optical waveguide structure. The fourth semiconductor layer is of a second conductivity type. The fourth semiconductor layer is located between the end face of the waveguide photodiode structure and the end face of the optical waveguide structure. The fourth semiconductor layer is in contact with the multiplication layer of the end face of the waveguide photodiode structure.

[0006] The present disclosure provides a semiconductor light receiving element. The semiconductor light receiving element includes a first semiconductor layer, a photodiode structure and a seventh semiconductor layer. The first semiconductor layer is of a first conductivity type. The photodiode structure is disposed on the first semiconductor layer. The photodiode structure has an end face. The photodiode structure includes a light absorbing layer, a second semiconductor layer, a multiplication layer and a third semiconductor layer. The light absorbing layer is of an intrinsic conductivity type or a first conductivity type. The second semiconductor layer is of a first conductivity type. The multiplication layer is of an intrinsic conductivity type or a first conductivity type. The third semiconductor layer is of a second conductivity type. The seventh semiconductor layer is of a second conductivity type. The seventh semiconductor layer contacts the multiplication layer on the end face of the photodiode structure. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 is a plan view illustrating a configuration of a light receiving device including an optical waveguide type light receiving element as a semiconductor light receiving element according to the first embodiment.

[0008] Figure 2 is an example of Figure 1 A view of a cross section along line II-II illustrated in FIG.

[0009] Figure 3 It is an example Figure 2 An enlarged cross-sectional view of a portion of the.

[0010] Figure 4 is an example of Figure 1 A view of a cross section along line IV-IV illustrated in FIG.

[0011] Figure 5 is an example of Figure 1 A view of a cross section of line VV illustrated in FIG.

[0012] Figure 6 is a cross-sectional view illustrating the structure of an optical waveguide type light receiving element as a comparative example, and illustrates the Figure 1 The cross section corresponding to the line VV in .

[0013] Fig. 7A and Figure 7B is a diagram for describing the depletion range and electric field strength in a comparative example.

[0014] Fig. 8A and Figure 8B is a diagram for describing the depletion range and the electric field intensity in the first embodiment.

[0015] Fig. 9 is a cross-sectional view illustrating the structure of an optical waveguide type light receiving element according to a first modification, and illustrates Figure 1 The cross section corresponding to the line VV in .

[0016] Fig.10 is a cross-sectional view illustrating the structure of an optical waveguide type light receiving element according to a second modification, and illustrates Figure 1 The cross section corresponding to the line VV in .

[0017] Fig.11 is a cross-sectional view illustrating the structure of an optical waveguide type light receiving element according to a third modification, and illustrates Figure 1 The cross section corresponding to the line VV in .

[0018] Fig.12 is a plan view illustrating an example of an optical waveguide type light receiving element.

[0019] Fig.13 is a cross-sectional view illustrating the structure of a semiconductor light receiving element according to the second embodiment. DETAILED DESCRIPTION

[0020] [Problems to be Solved by the Present Disclosure]

[0021] In recent years, an optical waveguide type light receiving element in which an optical waveguide structure and a waveguide type photodiode structure are integrated on a common substrate has been studied and developed. For example, such an optical waveguide type light receiving element is used as a receiving front end of an optical transmission system having a high transmission rate such as 40 Gb / s or more and in which a multi-level modulation method and a digital coherent receiving method are combined. The optical waveguide type light receiving element is manufactured by forming a butt joint structure on a substrate, the butt joint structure being composed of a semiconductor stacking unit of a photodiode including a light absorbing layer and a semiconductor stacking unit of an optical waveguide including an optical waveguide core layer.

[0022] For example, as in the aforementioned optical waveguide type light receiving element, the semiconductor light receiving element used as the receiving front end of the optical transmission system may need to have a high receiving sensitivity. As a solution, it is conceivable to give the waveguide type photodiode structure an avalanche multiplication effect. In this case, it is preferred that a multiplication layer for avalanche multiplication is provided between the light absorption layer constituting the photodiode and the semiconductor layer thereon. However, in many cases, the butt joint interface is formed by wet etching, so the butt joint interface is inclined relative to the direction perpendicular to the main surface of the substrate (for example, refer to JP2013-110207A). Therefore, the end face (butt joint interface) of the multiplication layer is also inclined relative to this direction. In this case, compared with other parts in the multiplication layer, depletion does not advance to the part near the end face of the multiplication layer, and therefore, the depletion range of the part near the end face of the multiplication layer is narrowed compared with the depletion range of other parts in the multiplication layer. Therefore, the maximum electric field (Emax) in the part near the end face of the multiplication layer becomes larger than that in other parts in the multiplication layer. As a result, edge breakdown is likely to occur.

[0023] [Effects of the present disclosure]

[0024] According to the semiconductor light receiving element of the present disclosure, the depletion ranges of the multiplication layers used for avalanche multiplication can be made substantially uniform.

[0025] [Description of the Embodiments of the Present Disclosure]

[0026] According to an embodiment, a semiconductor light receiving element including a first semiconductor layer, a waveguide photodiode structure, an optical waveguide structure and a fourth semiconductor layer is provided. The first semiconductor layer is of a first conductivity type. The waveguide photodiode structure has an end face arranged on the first semiconductor layer. The waveguide photodiode structure includes a light absorption layer, a second semiconductor layer, a multiplication layer and a third semiconductor layer. The light absorption layer is of an intrinsic conductivity type or a first conductivity type. The second semiconductor layer is of a first conductivity type. The multiplication layer is of an intrinsic conductivity type or a first conductivity type. The third semiconductor layer is of a second conductivity type. The optical waveguide structure has an end face arranged on the first semiconductor layer. The optical waveguide structure includes an optical waveguide core layer and a cladding layer. The end face of the waveguide photodiode structure faces the end face of the optical waveguide structure. The fourth semiconductor layer is of a second conductivity type. The fourth semiconductor layer is located between the end face of the waveguide photodiode structure and the end face of the optical waveguide structure. The fourth semiconductor layer is in contact with the multiplication layer of the end face of the waveguide photodiode structure.

[0027] In the semiconductor light receiving element, the waveguide photodiode structure includes a multiplication layer and a second semiconductor layer. The multiplication layer is a carrier multiplication layer arranged between a third semiconductor layer of the second conductivity type and a light absorption layer. The multiplication layer is of the first conductivity type or an intrinsic conductivity type. The second semiconductor layer is an electric field reduction layer arranged between the multiplication layer and the light absorption layer and is of the first conductivity type. In this way, since the waveguide photodiode structure includes the multiplication layer and the second semiconductor layer, a waveguide photodiode structure with an avalanche multiplication effect can be obtained. As described above, when the end face of the multiplication layer is inclined, the depletion does not advance to the portion near the end face of the multiplication layer compared to other portions in the multiplication layer, and therefore, the depletion range of the portion near the end face of the multiplication layer is narrowed compared to other portions in the multiplication layer. In contrast, in the semiconductor light receiving element, a fourth semiconductor layer belonging to the second conductivity type is arranged between the optical waveguide core layer and the waveguide photodiode structure and is in contact with the multiplication layer. In this case, when a reverse bias is applied, the portion near the end face of the multiplication layer is supplemented with carriers from the fourth semiconductor layer, and therefore the depletion range of the portion near the end face of the multiplication layer is expanded. That is, according to the semiconductor light receiving element, the depletion range of the multiplication layer can be made substantially uniform from the center portion to the portion near the end face. As a result, the local increase of the maximum electric field (Emax) in the multiplication layer is suppressed, and edge breakdown can be made less likely to occur.

[0028] In the aforementioned semiconductor light receiving element, the impurity concentration of the fourth semiconductor layer may be lower than that of the third semiconductor layer. According to this configuration, light loss caused by the fourth semiconductor layer can be reduced compared to the case where the impurity concentration of the fourth semiconductor layer is equal to or higher than that of the third semiconductor layer.

[0029] The aforementioned semiconductor light receiving element may further include a fifth semiconductor layer. The fifth semiconductor layer is disposed between the first semiconductor layer and the light absorbing layer, is a first conductivity type having a lower impurity concentration than the first semiconductor layer, and extends between the first semiconductor layer and the optical waveguide core layer. In this case, the depletion region when a reverse bias is applied extends from the light absorbing layer to the fifth semiconductor layer. Therefore, compared with a case where the fifth semiconductor layer is not provided, the electrostatic capacitance is reduced, and the CR time constant (C: capacitance, R: resistance) can be further reduced. As a result, a faster (broadband) high-frequency response characteristic can be achieved.

[0030] In the aforementioned semiconductor light receiving element, the waveguide type photodiode structure may further include a sixth semiconductor layer. The sixth semiconductor layer is disposed between the first semiconductor layer and the light absorbing layer, and is of the first conductivity type having a lower impurity concentration than the first semiconductor layer. In this case, by adjusting the thickness of the sixth semiconductor layer, the center position of the light absorbing layer in the thickness direction can be accurately aligned with the center position of the optical waveguide layer in the thickness direction. Therefore, even when the light absorbing layer is thinned, the coupling loss can be reduced by matching the mode field of the light absorbing layer with the optical waveguide core layer.

[0031] The aforementioned semiconductor light receiving element may also include a semiconductor passivation film arranged in the waveguide photodiode structure. In addition, the light absorption layer, the second semiconductor layer, the multiplication layer and the third semiconductor layer may constitute a striped mesa structure extending in the first direction as the arrangement direction of the waveguide photodiode structure and the optical waveguide structure. The striped mesa structure may have a pair of side surfaces extending in the first direction. The semiconductor passivation film may be in contact with the pair of side surfaces. In this case, the fourth semiconductor layer does not contact the pair of side surfaces of the striped mesa structure. Therefore, the light propagating in the optical waveguide structure can be efficiently incident on the waveguide photodiode structure.

[0032] In the aforementioned semiconductor light receiving element, the impurity concentration of the fourth semiconductor layer may be 3×10 16 cm -3 or less. In this case, the depletion region when a reverse bias is applied extends to the fourth semiconductor layer, so that the increase in the electric field near the end face of the waveguide type photodiode structure can be suppressed. In addition, the free carrier absorption loss caused by impurities during light propagation can be suppressed, and the transmittance of the optical waveguide can be improved.

[0033] In the aforementioned semiconductor light receiving element, the band gap of the fourth semiconductor layer may be greater than the band gap of the light absorbing layer and may be equal to or less than the band gap of the first semiconductor layer. In this case, the refractive index of the fourth semiconductor layer is equal to or greater than the refractive index of at least the first semiconductor layer. Therefore, the propagated light can be incident on the waveguide type photodiode structure without damaging the confinement effect of the propagated light in the waveguide.

[0034] According to another embodiment, a semiconductor light receiving element including a first semiconductor layer, a photodiode structure, and a seventh semiconductor layer is provided. The first semiconductor layer is of a first conductivity type. The photodiode structure is disposed on the first semiconductor layer. The photodiode structure has an end face. The photodiode structure includes a light absorbing layer, a second semiconductor layer, a multiplication layer, and a third semiconductor layer. The light absorbing layer is of an intrinsic conductivity type or a first conductivity type. The second semiconductor layer is of a first conductivity type. The multiplication layer is of an intrinsic conductivity type or a first conductivity type. The third semiconductor layer is of a second conductivity type. The seventh semiconductor layer is of a second conductivity type. The seventh semiconductor layer contacts the multiplication layer on the end face of the photodiode structure.

[0035] In addition, in the semiconductor light receiving element, similar to the waveguide type photodiode structure in the above-mentioned semiconductor light receiving element, the photodiode structure includes a multiplication layer and a second semiconductor layer. Therefore, a photodiode structure with an avalanche multiplication effect can be obtained. In addition, in the semiconductor light receiving element, a seventh semiconductor layer belonging to the second conductivity type is arranged adjacent to the photodiode structure. The seventh semiconductor layer contacts the multiplication layer on the end face of the photodiode structure. In addition, in this case, when a reverse bias is applied, the portion near the end face of the multiplication layer is supplemented with carriers from the seventh semiconductor layer, and therefore, the depletion range of the portion near the end face of the multiplication layer is expanded. That is, according to the semiconductor light receiving element, the depletion range of the multiplication layer can be made roughly consistent from the center portion to the portion near the end face. As a result, the local increase of the maximum electric field (Emax) in the multiplication layer is suppressed, and edge breakdown can be made less likely to occur.

[0036] [Details of the embodiment of the present invention]

[0037] Below, a specific example of a semiconductor light receiving element according to an embodiment of the present disclosure will be described with reference to the accompanying drawings. The present invention is not limited to the examples, but is indicated by the attached claims and is intended to include all modifications within the meaning and scope of the attached claims. In the following description, in the description of the drawings, the same elements will be designated by the same reference numerals, and redundant descriptions will be omitted.

[0038] (First embodiment)

[0039] Embodiments of the present disclosure relate to avalanche photodiodes (APDs) used in high-speed, high-capacity optical communication systems. Embodiments of the present disclosure relate to using waveguide structures to achieve fast, high-sensitivity performance and high reliability. Embodiments of the present disclosure relate to a multi-channel integrated optical receiving element in which a 90° hybrid function used in a digital coherent optical communication system is monolithically integrated. Embodiments of the present disclosure relate to using the integration of APD structures to achieve high-sensitivity performance and high reliability.

[0040] Figure 1 is a plan view illustrating a configuration of a light receiving device including an optical waveguide type light receiving element as a semiconductor light receiving element according to the first embodiment. Figure 2 Illustrated along the Figure 1 Cross section along line II-II illustrated in FIG. Figure 3 It is an example Figure 2 Magnified view of a portion of. Figure 4 Illustrated along the Figure 1 Cross section along line IV-IV illustrated in FIG. Figure 5 Illustrated along the Figure 1 A cross section of line VV is shown in FIG. Figure 5 In the figure, the insulating films 16 and 17 are omitted from illustration.

[0041] like Figure 1 As illustrated in FIG. 1 , the optical receiving device 1A according to the present embodiment includes an optical waveguide type optical receiving element 2A and signal amplifying units 3A and 3B. The optical receiving element 2A has a flat surface shape such as a substantially rectangular shape. For example, the optical receiving element 2A has a substrate made of a compound semiconductor such as InP and an optical waveguide formed on the substrate. The optical receiving element 2A has two input ports 4a and 4b and an optical branching portion (optical coupler) 5. The optical receiving element 2A also has optical receiving element portions 6a, 6b, 6c and 6d and capacitor portions 7a, 7b, 7c and 7d formed on the substrate. That is, the optical receiving element 2A has a structure in which the optical waveguide and the optical receiving element portions 6a, 6b, 6c and 6d are monolithically integrated on a common substrate.

[0042] The light receiving element 2A has a pair of end edges 2a and 2b extending in a predetermined direction A. Two input ports 4a and 4b are arranged at the end edge 2a which is one of the end edges 2a and 2b of the light receiving element 2A. An optical signal La including four signal components modulated by a quadrature phase shift keying (QPSK) method is input from the outside of the light receiving device 1A to the input port 4a which is one of the two input ports 4a and 4b. Local oscillation light Lb is input to the input port 4b. Each of the input ports 4a and 4b is optically coupled with the optical branching portion 5 via each of the optical waveguide portions 8a and 8b. The optical waveguide portions 8a and 8b are composed of a core layer and a cladding layer. The core layer is made of a material (e.g., InGaAsP) having a relatively large refractive index. The cladding layer is made of a material (e.g., InP) having a refractive index less than that of the core layer and covers the core layer.

[0043] The optical branching section 5 constitutes a 90° optical mixer. The optical branching section 5 is composed of a multimode interference (MMI) coupler. The optical branching section 5 causes the optical signal La and the local oscillator light Lb to interfere with each other, thereby branching the optical signal La into four signal components Lc1, Lc2, Lc3 and Lc4 modulated by the QPSK method. The polarization state of the signal component Lc1 is the same as the polarization state of the signal component Lc2, and the signal component Lc1 and the signal component Lc2 have an in-phase relationship. The polarization state of the signal component Lc3 is the same as the polarization state of the signal component Lc4, and the polarization states of the signal components Lc3 and Lc4 are different from the polarization states of the signal components Lc1 and Lc2. The signal components Lc3 and Lc4 have an orthogonal relationship.

[0044] Each of the light receiving element parts 6a, 6b, 6c and 6d has a configuration as an avalanche multiplication type PIN photodiode. The light receiving element parts 6a, 6b, 6c and 6d are arranged side by side in sequence along the end edge 2b of the light receiving element 2A. The light receiving element parts 6a, 6b, 6c and 6d are optically coupled with the corresponding output ports of the light branching part 5 via the optical waveguide parts 8c, 8d, 8e and 8f respectively. A consistent bias voltage is supplied to the cathode of the light receiving element parts 6a, 6b, 6c and 6d. Each of the light receiving element parts 6a, 6b, 6c and 6d receives each of the four signal components Lc1, Lc2, Lc3 and Lc4 from the light branching part 5, and generates an electrical signal (photoelectric current) corresponding to the light intensity of each of these signal component amounts Lc1, Lc2, Lc3 and Lc4. Electrode pads 21a, 21b, 21c and 21d are set on the light receiving element 2A to output signals. The electrode pads 21a, 21b, 21c, and 21d are electrically connected to the anodes of the light receiving element portions 6a, 6b, 6c, and 6d. The electrode pads 21a, 21b, 21c, and 21d are arranged side by side in the direction A along the end edge 2b of the light receiving element portion 2A. Each of the electrode pads 21a, 21b, 21c, and 21d is electrically connected to each of the electrode pads 61a, 61b, 61c, and 61d of the signal amplifying units 3A and 3B via each of the bonding wires 20a, 20b, 20c, and 20d.

[0045] The capacitor sections 7a, 7b, 7c and 7d are so-called metal-insulator-metal (MIM) capacitors. The capacitor sections 7a, 7b, 7c and 7d are composed of a ground layer made of a semiconductor, a lower metal layer and an upper metal layer stacked on the ground layer, and an insulating film ( Figure 2 The insulating film 17 is composed of an insulating film 17 illustrated in FIG. 1 . For example, each of the lower metal layer and the upper metal layer has a stacked structure such as TiW / Au or Ti / Au / Pt. The capacitor portions 7a, 7b, 7c and 7d are arranged side by side (adjacent to each other) in direction A relative to the corresponding light receiving element portions 6a, 6b, 6c and 6d on the light receiving element 2A. Each of the capacitor portions 7a, 7b, 7c and 7d is electrically connected between a bias wiring for supplying a bias voltage to each cathode of the light receiving element portion 6a, 6b, 6c or 6d and a reference potential wiring (GND line). The opening of the insulating film 17 is provided on a portion of the lower metal layer that is not covered by the upper metal layer. The bias wiring 42 (refer to Figure 2) is arranged on the lower metal layer exposed by the opening. The lower metal layer is electrically connected to the bias wiring 42. The reference potential (GND) wiring is arranged on the upper metal layer. The upper metal layer is electrically connected to the reference potential wiring. Due to each of the capacitor portions 7a, 7b, 7c and 7d, the inductance components between each cathode of the light receiving element portions 6a, 6b, 6c and 6d and the bypass capacitor (not illustrated) can be consistent in design.

[0046] Each of the capacitor sections 7a, 7b, 7c, and 7d has each of the electrode pads 22a, 22b, 22c, and 22d (for bias voltage) connected to the lower metal layer, and has each of the electrode pads 23a, 23b, 23c, and 23d (for reference potential) connected to the upper metal layer. Each of the electrode pads 23a, 23b, 23c, and 23d is provided between each of the electrode pads 22a, 22b, 22c, and 22d and the end edge 2b of the light receiving element 2A in the direction B intersecting (e.g., orthogonal to) the direction A.

[0047] One end of each of the bonding wires 20i, 20j, 20k, and 20m is connected to each of the electrode pads 22a, 22b, 22c, and 22d. The other end of each of the bonding wires 20i, 20j, 20k, and 20m is electrically connected to a bias voltage source (not illustrated). The bonding wires 20i, 20j, 20k, and 20m constitute a portion of wiring for supplying a bias voltage to the corresponding light receiving element portions 6a, 6b, 6c, and 6d.

[0048] One end of each of the bonding wires 20e, 20f, 20g, and 20h is connected to each of the electrode pads 23a, 23b, 23c, and 23d. Each of the bonding wires 20e, 20f, 20g, and 20h is arranged along each of the bonding wires 20a, 20b, 20c, and 20d. The other end of each of the bonding wires 20e, 20f, 20g, and 20h is connected to each of the electrode pads 62a, 62c, 62d, and 62f for the reference potential of the signal amplification units 3A and 3B.

[0049] The signal amplification units 3A and 3B are amplifiers (transimpedance amplifiers: TIA) for amplifying the electrical signals (photoelectric currents) output from the light receiving element parts 6a, 6b, 6c, and 6d. The signal amplification unit 3A has two electrode pads 61a and 61b for inputting signals. The signal amplification unit 3A performs differential amplification on the electrical signals input to the electrode pads 61a and 61b and generates a voltage signal. The signal amplification unit 3B has two electrode pads 61c and 61d for inputting signals. The signal amplification unit 3B performs differential amplification on the electrical signals input to the electrode pads 61c and 61d and generates a voltage signal. The electrode pads 61a, 61b, 61c, and 61d are arranged side by side in sequence in direction A along the end edge 2b of the light receiving element 2A. As described above, each of the electrode pads 61a, 61b, 61c, and 61d is electrically connected to each of the electrode pads 21a, 21b, 21c, and 21d via each of the bonding wires 20a, 20b, 20c, and 20d.

[0050] The signal amplification unit 3A also has three electrode pads 62a, 62b and 62c. The electrode pads 62a, 62b and 62c are arranged side by side in sequence in direction A along the end edge 2b of the light receiving element 2A. The electrode pad 61a is arranged between the electrode pads 62a and 62b. The electrode pad 61b is arranged between the electrode pads 62b and 62c. Similarly, the signal amplification unit 3B also has three electrode pads 62d, 62e and 62f. The electrode pads 62d, 62e and 62f are arranged side by side in sequence in direction A along the end edge 2b of the light receiving element 2A. The electrode pad 61c is arranged between the electrode pads 62d and 62e. The electrode pad 61d is arranged between the electrode pads 62e and 62f. As described above, each of the electrode pads 62a, 62c, 62d, and 62f of the signal amplifying units 3A and 3B is electrically connected to each of the electrode pads 23a, 23b, 23c, and 23d via each of the bonding wires 20e, 20f, 20g, and 20h.

[0051] Figure 2 The cross-sectional structures of two light receiving element portions 6 c and 6 d among the four light receiving element portions 6 a , 6 b , 6 c , and 6 d are illustrated. Figure 3 The cross-sectional structure of the light receiving element portion 6d is illustrated. The remaining light receiving element portions 6a and 6b have cross-sectional structures similar to these. Figure 4 The cross-sectional structure of one optical waveguide portion 8f among the six optical waveguide portions 8a, 8b, 8c, 8d, 8e, and 8f is illustrated. The remaining optical waveguide portions 8a, 8b, 8c, 8d, and 8e also have cross-sectional structures similar to this. Figure 5The cross-sectional structure of the joint portion between the light receiving element portion 6d and the optical waveguide portion 8f is illustrated. The joint portion between the light receiving element portion 6a and the optical waveguide portion 8c, the joint portion between the light receiving element portion 6b and the optical waveguide portion 8d, and the joint portion between the light receiving element portion 6c and the optical waveguide portion 8e also have a similar cross-sectional structure.

[0052] like Figure 5 As illustrated in FIG. 1 , the light receiving element portions 6a, 6b, 6c and 6d and the optical waveguide portions 8c, 8d, 8e and 8f are integrated on a common substrate 9. For example, the substrate 9 is a semi-insulating InP substrate. The cross-sectional structure of the light receiving element portions 6a, 6b, 6c and 6d will be described by taking the light receiving element portion 6d as an example. Figure 3 As shown in the example, the light receiving element portion 6d has an n-type semiconductor layer 10 and a waveguide type photodiode structure 19. The n-type semiconductor layer 10 is provided on the substrate 9 and is a high-concentration n-type conductive type (first conductive type). The photodiode structure 19 is provided in a region D (first region, see Figure 5 )superior.

[0053] The photodiode structure 19 has a light absorbing layer 13, a semiconductor layer 14 and a p-type contact layer 15. The light absorbing layer 13 is disposed on the n-type semiconductor layer 10. The semiconductor layer 14 is disposed on the light absorbing layer 13 and is of p-type conductivity (second conductivity type). The p-type contact layer 15 is disposed on the p-type semiconductor layer 14 and is of p-type conductivity. In addition, the photodiode structure 19 has a multiplication layer 11 and an n-type electric field control layer 12. The multiplication layer 11 is disposed between the light absorbing layer 13 and the p-type semiconductor layer 14. The n-type electric field control layer 12 is disposed between the multiplication layer 11 and the light absorbing layer 13. The n-type semiconductor layer 10 is the first semiconductor layer according to the present embodiment. The n-type electric field control layer 12 is the second semiconductor layer according to the present embodiment. The p-type semiconductor layer 14 is the third semiconductor layer according to the present embodiment.

[0054] The n-type semiconductor layer 10 and the n-type ohmic electrode 41 (see Figure 3 ) ohmic contact. For example, the n-type semiconductor layer 10 is an InP layer doped with Si. For example, the Si doping concentration of the n-type semiconductor layer 10 is 1×10 17 cm -3 For example, the thickness of the n-type semiconductor layer 10 is in the range of 1 μm to 2 μm.

[0055] The light absorbing layer 13 is of intrinsic (undoped) conductivity type or of n-type conductivity type having a lower impurity concentration than the n-type semiconductor layer 10. For example, the light absorbing layer 13 is a non-doped InGaAs layer or a layer having a Si doping concentration of 3×10 16 cm -3The p-type semiconductor layer 14 is a Zn-doped InP layer. For example, the Zn doping concentration of the p-type semiconductor layer 14 is 2×10 17 cm -3 or higher. For example, the thickness of the p-type semiconductor layer 14 is in the range of 1 μm to 2.5 μm. For example, the p-type contact layer 15 is an InGaAs layer doped with Zn. For example, the Zn doping concentration of the p-type contact layer 15 is 1×10 18 cm -3 For example, the thickness of the p-type contact layer 15 is in the range of 0.1 μm to 0.3 μm.

[0056] The multiplication layer 11 is a hole injection type carrier multiplication layer. The multiplication layer 11 is an intrinsic (undoped) conductivity type or an n-type conductivity type having an impurity concentration lower than that of the n-type semiconductor layer 10. In the present embodiment, the impurity concentration of the multiplication layer 11 is lower than the impurity concentration of the p-type semiconductor layer 14 and lower than the impurity concentration of the n-type electric field control layer 12. For example, the multiplication layer 11 is an undoped InP layer. For example, the thickness of the multiplication layer 11 is in the range of 0.050 μm to 0.200 μm.

[0057] The n-type electric field control layer 12 is a layer provided to reduce the electric field of the light absorption layer 13. The n-type electric field control layer 12 is an n-type conductive layer having a higher impurity concentration than the light absorption layer 13. The band gap of the n-type electric field control layer 12 is larger than the band gap of the light absorption layer 13 and is equal to the band gap of the n-type semiconductor layer 10 or smaller than the band gap of the n-type semiconductor layer 10. For example, the n-type electric field control layer 12 is an InP layer doped with Si or an InAlGaAs layer doped with Si. For example, the Si doping concentration of the n-type electric field control layer 12 is 1×10 18 cm -3 For example, the thickness of the n-type electric field control layer 12 is in the range of 0.025 μm to 0.100 μm.

[0058] A composition grading layer may be provided between the light absorbing layer 13 and the n-type electric field control layer 12 to reduce the heterogeneous energy barrier (ΔEv and ΔEc) between the two layers. The composition grading layer is of undoped conductivity type or has a Si doping concentration of 1×10 17 cm -3 or lower n-type conductivity type. A p-type heterogeneous barrier mitigation layer may be provided between the p-type semiconductor layer 14 and the p-type contact layer 15. For example, the heterogeneous barrier mitigation layer may be formed by a doping concentration of 1×10 18 cm -3 For example, the band gap wavelengths of the two Zn-doped InGaAsP layers are 1.1 μm and 1.3 μm, respectively.

[0059] The light receiving element portion 6d further has a semiconductor passivation film 18 disposed in a photodiode structure 19. Part of the n-type semiconductor layer 10, the light absorption layer 13, the n-type electric field control layer 12, the multiplication layer 11, the p-type semiconductor layer 14, and the p-type contact layer 15 constitute a striped mesa structure extending in the optical waveguide direction (first direction). The striped mesa structure has a pair of side surfaces 19a extending in the optical waveguide direction. In the present embodiment, the optical waveguide direction is a direction B that intersects or is orthogonal to the direction A (refer to FIG. 1 ). Figure 1 ). The semiconductor passivation film 18 is in contact with the entire surface of each of the side surfaces 19a. The semiconductor passivation film 18 constitutes an embedding region for embedding the photodiode structure 19 on both side surfaces 19a. For example, the semiconductor passivation film 18 is made of a material such as undoped InP or a material with a doping concentration of 1×10 16 cm -3 or lower Zn-doped InP semi-insulating material. For example, in the direction of the optical waveguide ( Figure 1 The width of the stripe mesa structure in a direction perpendicular to the direction A) in the range of 1.5 μm to 3 μm. For example, the height of the stripe mesa structure is in the range of 2 μm to 3.5 μm.

[0060] The light receiving element portion 6d also has insulating films 16 and 17. The insulating films 16 and 17 are provided from the upper surface of the striped mesa structure to the portion on the semiconductor passivation film 18. The insulating films 16 and 17 cover and protect the upper surface of the striped mesa structure and the semiconductor passivation film 18. For example, the insulating films 16 and 17 are made of a material such as SiN, SiON, or SiO 2 The insulating films 16 and 17 have openings on the upper surface of the stripe mesa structure. A p-type ohmic electrode 31 is provided on the p-type contact layer 15 exposed from the insulating films 16 and 17 through the openings.

[0061] For example, the p-type ohmic electrode 31 is made of an alloy of AuZn or Pt and the p-type contact layer 15. A wiring 32 is provided on the p-type ohmic electrode 31. The wiring 32 extends in the optical waveguide direction ( Figure 1 The wiring 32 extends in the direction B) in the middle and electrically connects the p-type ohmic electrode 31 and the electrode pad 21d to each other. For example, the wiring 32 has a stacked structure such as TiW / Au or Ti / Pt / Au. For example, the electrode pad 21d is formed by Au plating.

[0062] The insulating films 16 and 17 also have another opening on the portion of the n-type semiconductor layer 10 located outside the mesa structure of the light receiving element portion 6d. An n-type ohmic electrode 41 serving as a cathode is provided on the n-type semiconductor layer 10 exposed from the insulating films 16 and 17 through the opening. For example, the n-type ohmic electrode 41 is made of an alloy of AuGe or AuGeNi and the n-type semiconductor layer 10. A bias wiring 42 is provided on the n-type ohmic electrode 41. The bias wiring 42 extends to the lower metal layer of the capacitor portion 7d and electrically connects the lower metal layer and the n-type ohmic electrode 41 to each other.

[0063] The capacitor section 7d is formed by stacking an insulating film 16, a lower metal layer, an insulating film (interlayer film) 17, and an upper metal layer in this order on a substrate 9. For example, the upper metal layer and the lower metal layer are formed of a stacked structure such as TiW / Au or Ti / Au / Pt. An opening is formed in the insulating film 17 on a portion of the lower metal layer that is not covered by the upper metal layer. A bias wiring 42 is provided on the lower metal layer exposed by the opening. The bias wiring 42 is provided at a position where it is in the optical waveguide direction ( Figure 1 The wiring is arranged on the upper metal layer, and the ...

[0064] A through hole 51 is provided on the substrate 9. The through hole 51 is a metal conductive material and is formed, for example, by Au plating. The through hole 51 is provided in such a manner that the substrate 9 penetrates from the front surface to the rear surface. The upper metal layer of the capacitor portion 7d is electrically connected to one end of the through hole 51 on the front surface side via the electrode pad 23d. The other end of the through hole 51 on the rear surface side is connected to a reference potential line (ground potential line) shared between the signal amplification units 3A and 3B.

[0065] For example, the wiring connected to the electrode pad 23d, and the bias wiring 42 have a laminated structure such as TiW / Au or Ti / Au / Pt. For example, the electrode pad 23d and the electrode pad 22d are formed by Au plating.

[0066] Subsequently, the cross-sectional structure of the optical waveguide portion will be described. Figure 4 and Figure 5 As shown in the example, the optical waveguide portion 8f includes an n-type semiconductor layer 10 and an optical waveguide structure 80. The n-type semiconductor layer 10 is provided on a substrate 9. The optical waveguide structure 80 is provided on a region E (second region) of the n-type semiconductor layer 10. The region E is a region in the optical waveguide direction ( Figure 1The optical waveguide structure 80 is adjacent to the region D of the n-type semiconductor layer 10 in the direction B). The optical waveguide structure 80 includes an optical waveguide layer 81 disposed on the n-type semiconductor layer 10 and a cladding layer 82 disposed on the optical waveguide layer 81.

[0067] The n-type semiconductor layer 10 is the same as the n-type semiconductor layer 10 of the light receiving element portion 6d, and is used as a lower cladding layer in the optical waveguide portion 8f. The n-type semiconductor layer 10 is provided from the light receiving element portion 6d to the optical waveguide portion 8f on the substrate 9. The composition, doping concentration, and thickness of the n-type semiconductor layer 10 in the optical waveguide portions 8a, 8b, 8c, 8d, 8e, and 8f are the same as those of the n-type semiconductor layer 10 in the light receiving element portion 6d.

[0068] like Figure 5 As illustrated in FIG, the optical waveguide portion 8f forms a butt joint coupled with the light receiving element portion 6d, and the optical waveguide layer 81 contacts the light absorbing layer 13. Therefore, the optical waveguide layer 81 is optically coupled with the light absorbing layer 13. For example, the butt joint interface is formed by wet etching. Therefore, the butt joint interface is inclined relative to the direction perpendicular to the upper surface 10a of the n-type semiconductor layer 10 (that is, the interface between the n-type semiconductor layer 10 and the light absorbing layer 13). In other words, when the interface between the optical waveguide structure 80 and the photodiode structure 19 is the first interface C1 and the interface between the region D of the n-type semiconductor layer 10 and the photodiode structure 19 is the second interface C2, the angle θ formed by the first interface C1 and the second interface C2 is less than 90°. For example, the angle θ formed by the first interface C1 and the second interface C2 is in the range of 25° to 60°.

[0069] The optical waveguide layer 81 includes an optical waveguide core layer 83 and a p-type semiconductor layer 84 (fourth semiconductor layer). The p-type semiconductor layer 84 is provided on the region E of the n-type semiconductor layer 10. The optical waveguide core layer 83 is provided on the p-type semiconductor layer 84. That is, the p-type semiconductor layer 84 is provided between the region E of the n-type semiconductor layer 10 and the optical waveguide core layer 83.

[0070] The optical waveguide core layer 83 has a greater refractive index than the n-type semiconductor layer 10, and is formed of a material that can undergo lattice matching with the n-type semiconductor layer 10. For example, the optical waveguide core layer 83 is made of InGaAsP. For example, the band gap wavelength of InGaAsP of the optical waveguide core layer 83 is 1.05 μm. For example, the thickness of the optical waveguide core layer 83 is in the range of 0.3 μm to 0.5 μm.

[0071] The p-type semiconductor layer 84 has a greater refractive index than the n-type semiconductor layer 10 and is formed of a material that can undergo lattice matching with the n-type semiconductor layer 10. The band gap of the p-type semiconductor layer 84 is greater than the band gap of the light absorbing layer 13 and is equal to the band gap of the n-type semiconductor layer 10 or less than the band gap of the n-type semiconductor layer 10. For example, the material of the p-type semiconductor layer 84 is InGaAsP. As an example, the band gap wavelength of InGaAsP of the p-type semiconductor layer 84 is equal to the band gap wavelength of the optical waveguide core layer 83. For example, the band gap wavelength of InGaAsP of the p-type semiconductor layer 84 is 1.05 μm. The impurity concentration of the p-type semiconductor layer 84 is lower than the impurity concentration of the p-type semiconductor layer 14. For example, the p-type semiconductor layer 84 is a layer whose Zn doping concentration is 3×10 16 cm -3 The p-type semiconductor layer 84 is a low-concentration p-type InGaAs layer having a thickness of 0.050 μm to 0.200 μm, for example.

[0072] The p-type semiconductor layer 84 rises on the end surface of the photodiode structure 19 along the first interface C1 and extends between the optical waveguide core layer 83 and the photodiode structure 19. In the first interface C1, the p-type semiconductor layer 84 is in contact with the light absorption layer 13, the n-type electric field control layer 12, the multiplication layer 11, and the p-type semiconductor layer 14. For example, the thickness of the portion of the p-type semiconductor layer 84 adjacent to the multiplication layer 11 is in the range of 0.05 μm to 0.5 μm.

[0073] The cladding layer 82 has a smaller refractive index than the optical waveguide layer 81, and is formed of a material that can undergo lattice matching with the optical waveguide layer 81. For example, the cladding layer 82 is made of undoped InP. For example, the thickness of the cladding layer 82 is in the range of 1 μm to 3 μm, and the height of the upper surface of the cladding layer 82 is aligned with the height of the upper surface of the p-type contact layer 15.

[0074] like Figure 4 As shown in the example, the n-type semiconductor layer 10, the optical waveguide layer 81 and the cladding layer 82 constitute a portion of the optical waveguide direction ( Figure 1 The mesa structure is a mesa structure extending in the direction B in the middle. Due to the difference between the refractive indexes of the mesa structure and the n-type semiconductor layer 10, the cladding layer 82 and the optical waveguide layer 81, the optical signal is confined in the optical waveguide layer 81. Therefore, the optical signal can propagate to the light receiving element portion 6d. The side surface and the upper surface of the mesa structure are protected by being covered by the insulating films 16 and 17.

[0075] The effect obtained by the light receiving element 2A of the present embodiment having the aforementioned configuration will be described. In the light receiving element 2A, the photodiode structure 19 includes a multiplication layer 11 and an n-type electric field control layer 12. The multiplication layer 11 is a carrier multiplication layer arranged between the p-type semiconductor layer 14 and the light absorption layer 13. The multiplication layer 11 is an n-type conductive type having an impurity concentration lower than that of the n-type electric field control layer 12 or is an undoped layer. The n-type electric field control layer 12 is an electric field reducing layer arranged between the multiplication layer 11 and the light absorption layer 13 and is of an n-type conductive type. Since the photodiode structure 19 includes the multiplication layer 11 and the n-type electric field control layer 12, a photodiode structure 19 having an avalanche multiplication effect can be obtained.

[0076] Figure 6 is a cross-sectional view illustrating the structure of an optical waveguide type light receiving element 102 as a comparative example, and illustrates the structure of Figure 1 The cross section corresponding to the line VV in . Fig. 7A and Figure 7B 8 is a view used to describe the depletion range and electric field strength in the comparative example. The optical waveguide type light receiving element 102 is different from the light receiving element 2A in that an optical waveguide structure 80X is included to replace the optical waveguide structure 80, and its configuration is similar to the configuration of the light receiving element 2A otherwise. The optical waveguide structure 80X includes an optical waveguide layer 81X and a cladding layer 82. The optical waveguide layer 81X is composed only of an optical waveguide core layer and does not have a p-type semiconductor layer 84. The optical waveguide core layer constituting the optical waveguide layer 81X is made of the same material as the optical waveguide core layer 83 (for example, InGaAsP). In addition, the band gap wavelength of the InGaAsP of the optical waveguide core layer constituting the optical waveguide layer 81X is equal to the band gap wavelength of the InGaAsP of the optical waveguide core layer 83.

[0077] In many cases, since the butt joint interface is formed by wet etching, it becomes a front face structure and is inclined toward the photodiode side relative to the direction perpendicular to the main surface of substrate 9. Therefore, the end face of multiplication layer 11 is also inclined in a similar manner. Fig. 7A is an enlarged view of a portion near the end face of the multiplication layer 11 in this case. The area surrounded by the dotted line in the diagram represents a depleted area. When the end face 11j of the multiplication layer 11 is tilted, the length of the interface between the n-type electric field control layer 12 and the multiplication layer 11 in the optical waveguide direction becomes shorter than the length of the interface between the light absorption layer 13 and the multiplication layer 11 in the same direction, depending on its tilt angle. Therefore, if the p-type semiconductor layer 84 does not extend between the optical waveguide core layer 83 and the photodiode structure 19, the negative charge in the portion near the end face 11j of the multiplication layer 11 becomes insufficient when a reverse bias is applied. As a result, depletion does not proceed compared to other portions in the multiplication layer 11, and the depletion range Ws of this portion becomes narrower than the depletion range Wc of other portions.

[0078] Figure 7B 1 is a diagram illustrating the change in electric field strength in the thickness direction. Curve G11 shows the change in electric field strength in the vicinity of the end face 11j of the multiplication layer 11. Curve G12 shows the change in electric field strength in other parts of the multiplication layer 11. Figure 7B As illustrated in FIG. 1 , due to the relationship between the aforementioned depletion ranges Ws and Wc, the maximum electric field Emax1 in the portion near the end face 11j of the multiplication layer 11 becomes greater than the maximum electric field Emax2 in other portions of the multiplication layer 11. Therefore, edge breakdown is likely to occur in the butt joint interface. In addition, the multiplication current is concentrated in the portion near the end face 11j, so the reliability is deteriorated.

[0079] In the light receiving element 2A of the present embodiment, the p-type semiconductor layer 84 extends between the optical waveguide core layer 83 and the photodiode structure 19 and is in contact with the multiplication layer 11 and the n-type electric field control layer 12 in the first interface C1 . Fig. 8A and Figure 8B is a diagram for describing the depletion range and the electric field intensity according to the present embodiment. Fig. 8A 1 is an enlarged view of a portion near the end face of the multiplication layer 11 of the present embodiment. The region surrounded by the dotted line in the diagram represents a depleted region. When the p-type semiconductor layer 84 extends between the optical waveguide core layer 83 and the photodiode structure 19, when a reverse bias is applied, the portion near the end face 11j of the multiplication layer 11 is supplemented with carriers from the p-type semiconductor layer 84. Therefore, as Fig. 8A As shown in the example, the depletion range Ws of the portion near the end face 11j of the multiplication layer 11 is expanded. Therefore, the depletion range is made roughly consistent with the butt joint interface, and the non-uniformity of the depletion range caused by the inclination of the end face 11j is reduced. That is, according to the light receiving element 2A of this embodiment, the depletion range of the multiplication layer 11 can be made roughly consistent.

[0080] Figure 8B 1 is a view illustrating the change in the electric field intensity of the multiplication layer 11 in the thickness direction. According to the present embodiment, the maximum electric field Emax in the portion near the end surface 11j of the multiplication layer 11 becomes the same as the maximum electric field in other portions of the multiplication layer 11. That is, the local increase of the maximum electric field Emax in the multiplication layer 11 can be suppressed. Therefore, edge breakdown can be made less likely to occur. In addition, reliability degradation due to the concentration of the multiplication current can be avoided.

[0081] As in the present embodiment, the impurity concentration of the p-type semiconductor layer 84 may be lower than the impurity concentration of the p-type semiconductor layer 14. According to this configuration, compared with a case where the impurity concentration of the p-type semiconductor layer 84 is equal to or higher than the impurity concentration of the p-type semiconductor layer 14, light loss caused by the p-type semiconductor layer 84 may be reduced.

[0082] As in the present embodiment, the light receiving element 2A may further include a semiconductor passivation film 18 disposed in the photodiode structure 19. The light absorbing layer 13, the n-type electric field control layer 12, the multiplication layer 11 and the p-type semiconductor layer 14 constitute a semiconductor layer in the optical waveguide direction ( Figure 1 The striped mesa structure 80 may be a striped mesa structure extending in the direction B) in the optical waveguide direction, and the striped mesa structure may have a pair of side surfaces 19a extending in the optical waveguide direction. The semiconductor passivation film 18 may be in contact with the pair of side surfaces 19a. In this case, the p-type semiconductor layer 84 is not in contact with the pair of side surfaces 19a of the striped mesa structure. Therefore, light propagating in the optical waveguide structure 80 can be efficiently incident on the photodiode structure 19.

[0083] As in the present embodiment, the impurity concentration of the p-type semiconductor layer 84 may be 3×10 16 cm -3 According to this configuration, the depletion region when a reverse bias is applied expands to the p-type semiconductor layer 84, and an increase in the electric field near the first interface C1 of the photodiode structure 19 can be suppressed. In addition, free carrier absorption loss due to impurities when light propagates can be suppressed, and the transmittance of the waveguide can be improved.

[0084] As in the present embodiment, the band gap of the p-type semiconductor layer 84 may be larger than the band gap of the light absorbing layer 13 and may be equal to or smaller than the band gap of the n-type semiconductor layer 10. According to this configuration, the refractive index of the p-type semiconductor layer 84 is equal to or larger than the refractive index of the n-type semiconductor layer 10. Therefore, the propagating light may be efficiently incident on the photodiode structure 19 without impairing the confinement effect of the propagating light within the waveguide.

[0085] (First revised form)

[0086] Fig. 9 is a cross-sectional view illustrating the structure of an optical waveguide type light receiving element 2B according to a first modification of the aforementioned embodiment, and illustrates Figure 1 The light receiving element 2B is different from the light receiving element 2A in that a photodiode structure 19B is included instead of the photodiode structure 19, and its configuration is otherwise similar to that of the light receiving element 2A. In addition to the configuration of the photodiode structure 19, the photodiode structure 19B also includes a buffer layer 85 (fifth semiconductor layer).

[0087] The buffer layer 85 is disposed between the n-type semiconductor layer 10 and the light absorbing layer 13 and extends from a portion on the region D to a portion on the region E in the n-type semiconductor layer 10. The buffer layer 85 is an n-type conductive type having a lower impurity concentration than the n-type semiconductor layer 10 or an undoped conductive type. For example, the buffer layer 85 is an InP layer doped with Si. For example, the Si doping concentration of the buffer layer 85 is 1×10 16 cm -3 For example, the thickness of the buffer layer 85 is in the range of 0.050 μm to 0.300 μm. In the optical waveguide portion 8f, the buffer layer 85 is provided between the p-type semiconductor layer 84 and the n-type semiconductor layer 10 and serves as a second lower cladding layer.

[0088] In this modification, the depletion region when a reverse bias is applied expands from the light absorbing layer 13 to the buffer layer 85. Therefore, the electrostatic capacitance is reduced and the CR time constant can be further reduced compared to the case where the buffer layer 85 is not provided. As a result, faster (wideband) high-frequency response characteristics can be achieved.

[0089] (Second revised form)

[0090] Fig.10 is a cross-sectional view illustrating the structure of an optical waveguide type light receiving element 2C according to a second modification of the aforementioned embodiment, and illustrates Figure 1 The light receiving element 2C is different from the light receiving element 2A in that a photodiode structure 19C is included instead of the photodiode structure 19, and its configuration is otherwise similar to that of the light receiving element 2A. In addition to the configuration of the photodiode structure 19, the photodiode structure 19C also includes a heterogeneous barrier mitigation layer 86 (sixth semiconductor layer).

[0091] The heterogeneous barrier mitigation layer 86 is disposed between the region D of the n-type semiconductor layer 10 and the light absorbing layer 13. The heterogeneous barrier mitigation layer 86 has no portion extending onto the region E of the n-type semiconductor layer 10. The heterogeneous barrier mitigation layer 86 is disposed to mitigate the heterogeneous energy barrier between the n-type semiconductor layer 10 and the light absorbing layer 13.

[0092] The heterogeneous barrier mitigation layer 86 is an n-type conductive type having a lower impurity concentration than the n-type semiconductor layer 10 or an undoped conductive type. The band gap of the heterogeneous barrier mitigation layer 86 is between the band gap of the light absorption layer 13 and the band gap of the n-type semiconductor layer 10. In the present modification, the band gap of the heterogeneous barrier mitigation layer 86 is between the band gap of InGaAs and the band gap of InP. For example, the heterogeneous barrier mitigation layer 86 is an InGaAsP layer doped with Si, and, for example, its band gap wavelength is 1.25 μm or 1.40 μm. Alternatively, the heterogeneous barrier mitigation layer 86 may be a compositionally graded layer having a continuously varying band gap wavelength. For example, the Si doping concentration of the heterogeneous barrier mitigation layer 86 is 1×10 17 cm -3 For example, the thickness of the heterogeneous barrier mitigation layer 86 is in the range of 0.025 μm to 0.100 μm.

[0093] In the present modification, the center position of the light absorbing layer 13 in the thickness direction can be accurately aligned with the center position of the light waveguide layer 81 (i.e., the light waveguide core layer 83 and the p-type semiconductor layer 84) in the thickness direction by adjusting the thickness of the heterogeneous barrier mitigation layer 86. Therefore, even when the light absorbing layer 13 is thinned to increase the operating speed of the light receiving element 2C, the coupling loss can be reduced by matching the mode fields of the light absorbing layer 13 and the light waveguide layer 81. As a result, a reduction in coupling loss and high sensitivity can be achieved.

[0094] (Third revised form)

[0095] Fig.11 is a cross-sectional view illustrating the structure of an optical waveguide type light receiving element 2D according to a third modification of the aforementioned embodiment, and illustrates Figure 1 The light receiving element 2D has a configuration in which the hole injection type multiplication layer 11 of the aforementioned embodiment is changed into an electron injection type multiplication layer 111. The configuration of the light receiving element 2D is similar to that of the light receiving element 2A of the aforementioned embodiment except for the points described below.

[0096] Specifically, the light receiving element portion 6d of the light receiving element 2D has a p-type semiconductor layer 101 and a waveguide type photodiode structure 119. The p-type semiconductor layer 101 is provided on the substrate 9 and is a high concentration p-type conductive type (first conductive type). The photodiode structure 119 is provided on the region F (first region) of the p-type semiconductor layer 101. The photodiode structure 119 has a light absorbing layer 113, an n-type semiconductor layer 114, and an n-type contact layer 115. The light absorbing layer 113 is provided on the p-type semiconductor layer 101. The n-type semiconductor layer 114 is provided on the light absorbing layer 113 and is an n-type conductive type (second conductive type). The n-type contact layer 115 is provided on the n-type semiconductor layer 114. The photodiode structure 119 also has a multiplication layer 111 and a p-type electric field control layer 112. The multiplication layer 111 is provided between the light absorbing layer 113 and the n-type semiconductor layer 114. The p-type electric field control layer 112 is disposed between the multiplication layer 111 and the light absorption layer 113. The p-type semiconductor layer 101 is the first semiconductor layer according to this embodiment. The p-type electric field control layer 112 is the second semiconductor layer according to this embodiment. The n-type semiconductor layer 114 is the third semiconductor layer according to this embodiment.

[0097] The p-type semiconductor layer 101 is in ohmic contact with a p-type ohmic electrode (not shown). For example, the p-type semiconductor layer 101 is an InP layer doped with Zn. For example, the Zn doping concentration of the p-type semiconductor layer 101 is 1×10 18 cm -3 For example, the thickness of the p-type semiconductor layer 101 is in the range of 1 μm to 2 μm.

[0098] The light absorbing layer 113 is of intrinsic (undoped) conductivity type or of p-type conductivity type having a lower impurity concentration than the p-type semiconductor layer 101. For example, the light absorbing layer 113 is a non-doped InGaAs layer or a Zn doping layer having a Zn doping concentration of 3×10 16 cm -3 The light absorbing layer 113 may be a low-concentration p-type InGaAs layer of 0.1 μm to 0.4 μm. For example, the n-type semiconductor layer 114 may be an InP layer doped with Si. For example, the Si doping concentration of the n-type semiconductor layer 114 may be 2×10 17 cm -3 For example, the thickness of the n-type semiconductor layer 114 is in the range of 1 μm to 2.5 μm. For example, the n-type contact layer 115 is an InGaAs layer doped with Si. For example, the Si doping concentration of the n-type contact layer 115 is 1×10 18 cm -3 For example, the thickness of the n-type contact layer 115 is in the range of 0.1 μm to 0.3 μm. The n-type ohmic electrode 131 is provided on the n-type contact layer 115 .

[0099] The multiplication layer 111 is an electron injection type carrier multiplication layer. The multiplication layer 111 is an intrinsic (undoped) conductivity type or a p-type conductivity type having an impurity concentration lower than that of the p-type semiconductor layer 101. In this embodiment, the impurity concentration of the multiplication layer 111 is lower than the impurity concentration of the n-type semiconductor layer 114 and lower than the impurity concentration of the p-type electric field control layer 112. For example, the multiplication layer 111 is an InAlAs layer doped with Zn. For example, the Zn doping concentration of the multiplication layer 111 is 3×10 16 cm -3 For example, the thickness of the multiplication layer 111 is in the range of 0.050 μm to 0.200 μm.

[0100] The p-type electric field control layer 112 is provided to reduce the electric field of the light absorption layer 113. The p-type electric field control layer 112 is a p-type conductive type having a higher impurity concentration than the light absorption layer 113. The band gap of the p-type electric field control layer 112 is larger than the band gap of the light absorption layer 113 and is equal to the band gap of the p-type semiconductor layer 101 or smaller than the band gap of the p-type semiconductor layer 101. For example, the p-type electric field control layer 112 is a Zn-doped InP layer or a Zn-doped InAlGaAs layer. For example, the Zn doping concentration of the p-type electric field control layer 112 is 1×10 18 cm -3 For example, the thickness of the p-type electric field control layer 112 is in the range of 0.025 μm to 0.100 μm.

[0101] A composition graded layer may be provided between the light absorbing layer 113 and the p-type electric field control layer 112. The composition graded layer reduces the heterogeneous energy barrier (ΔEv and ΔEc) between the light absorbing layer 113 and the p-type electric field control layer 112. The composition graded layer is an undoped conductive type or has a Zn doping concentration of 1×10 17 cm -3 or lower p-type conductivity type. An n-type heterogeneous barrier mitigation layer may be provided between the n-type semiconductor layer 114 and the n-type contact layer 115. For example, the heterogeneous barrier mitigation layer may be formed by a doping concentration of 1×10 18 cm -3 For example, the band gap wavelengths of the two Si-doped InGaAsP layers are 1.1 μm and 1.3 μm, respectively.

[0102] In addition, in this embodiment, the light receiving element portion 6d further includes a semiconductor passivation film 18 (see Figure 3). A portion of the p-type semiconductor layer 101, the light absorption layer 113, the p-type electric field control layer 112, the multiplication layer 111, the n-type semiconductor layer 114, and the n-type contact layer 115 constitute a striped mesa structure extending in the optical waveguide direction (first direction). The striped mesa structure has a pair of side surfaces extending in the optical waveguide direction. In addition, in the present modification, the optical waveguide direction is a direction B that intersects or is orthogonal to the direction A (refer to Figure 1 ). The semiconductor passivation film 18 is in contact with the entire surface of each of the side surfaces of the stripe mesa structure. That is, similar to the side surface 19a, a pair of side surfaces of the stripe mesa structure are embedded by the embedded region composed of the semiconductor passivation film 18.

[0103] For example, the n-type ohmic electrode 131 is made of an alloy of AuZn or Pt and the n-type contact layer 115. In addition, a wiring 132 is provided on the n-type ohmic electrode 131. The wiring 132 extends in the optical waveguide direction and electrically connects the n-type ohmic electrode 131 and the electrode pad 21d to each other. For example, the wiring 132 has a stacked structure such as TiW / Au or Ti / Pt / Au.

[0104] The optical waveguide section 8f of the light receiving element 2D is configured to include the p-type semiconductor layer 101 and the optical waveguide structure 180. Figure 1 An optical waveguide structure 180 is provided on a region G (second region) adjacent to a region E of the p-type semiconductor layer 101 in a direction B in the direction of the optical waveguide. The p-type semiconductor layer 101 is provided from the light receiving element portion 6d to the optical waveguide portion 8f on the substrate 9. The p-type semiconductor layer 101 is the same as the p-type semiconductor layer 101 of the optical waveguide portion 8f. The p-type semiconductor layer 101 serves as a lower cladding layer in the optical waveguide portion 8f. In addition, in the present modified form, the composition, doping concentration and thickness of the p-type semiconductor layer 101 in the optical waveguide portions 8a, 8b, 8c, 8d, 8e and 8f are the same as the composition, doping concentration and thickness of the p-type semiconductor layer 101 of the light receiving element portion 6d.

[0105] The optical waveguide structure 180 has a configuration in which the optical waveguide layer 81 in the optical waveguide structure 80 is changed into the optical waveguide layer 181. The optical waveguide layer 181 has a configuration in which the p-type semiconductor layer 84 in the optical waveguide layer 81 is changed into an n-type semiconductor layer 184 (fourth semiconductor layer) of n-type conductivity type. The n-type semiconductor layer 184 is provided on the region G of the p-type semiconductor layer 101, and the optical waveguide core layer 83 is provided on the n-type semiconductor layer 184. That is, similar to the p-type semiconductor layer 84 in the optical waveguide layer 81, the n-type semiconductor layer 184 is provided between the region G of the p-type semiconductor layer 101 and the optical waveguide core layer 83.

[0106] The n-type semiconductor layer 184 has a greater refractive index than the p-type semiconductor layer 101 and is formed of a material that can undergo lattice matching with the p-type semiconductor layer 101. The band gap of the n-type semiconductor layer 184 is greater than the band gap of the light absorbing layer 113 and is equal to the band gap of the p-type semiconductor layer 101 or is smaller than the band gap of the p-type semiconductor layer 101. For example, the material of the n-type semiconductor layer 184 is InGaAsP. As an example, the band gap wavelength of InGaAsP of the n-type semiconductor layer 184 is equal to the band gap wavelength of the optical waveguide core layer 83. For example, the band gap wavelength of InGaAsP of the n-type semiconductor layer 184 is 1.05 μm. The impurity concentration of the n-type semiconductor layer 184 is lower than the impurity concentration of the n-type semiconductor layer 114. For example, the n-type semiconductor layer 184 is a layer whose Si doping concentration is 3×10 16 cm -3 The thickness of the portion of the n-type semiconductor layer 184 on the region G is, for example, in the range of 0.050 μm to 0.200 μm.

[0107] In addition, in the present embodiment, the n-type semiconductor layer 184 rises on the end surface of the photodiode structure 119 along the first interface C1 and extends between the optical waveguide core layer 83 and the photodiode structure 119. In the first interface C1, the n-type semiconductor layer 184 is in contact with the light absorption layer 113, the p-type electric field control layer 112, the multiplication layer 111, and the n-type semiconductor layer 114. For example, the thickness of the portion of the n-type semiconductor layer 184 adjacent to the multiplication layer 111 is in the range of 0.05 μm to 0.5 μm.

[0108] In the aforementioned embodiment, the hole injection type multiplication layer 11 in which the ionization rate of holes (β) is greater than the ionization rate of electrons (α) has been described as an example. In addition, in the present modification, even in the configuration including the electron injection type multiplication layer 111 in which α is greater than β, effects similar to those of the aforementioned embodiment can be exhibited.

[0109] In the above, the semiconductor light receiving element of the present disclosure has been specifically described based on examples, but the semiconductor light receiving element of the present disclosure is not limited to the aforementioned examples and can be changed within the scope not departing from the gist thereof. In the aforementioned embodiments, the configuration in which the optical waveguide portions 8a, 8b, 8c, 8d, 8e, and 8f and the light receiving element portions 6a, 6b, 6c, and 6d are integrated on the common substrate 9 has been described as an example. A photoelectric conversion circuit including other InP-based electronic devices (e.g., heterojunction bipolar transistors), capacitors, and resistors may be further integrated on the substrate 9.

[0110] In the above-mentioned embodiments and various modifications, the case where the configuration of the present disclosure is applied to an integrated light receiving element used by a coherent wave detection method using quadrature phase shift keying (QPSK) or quadrature amplitude modulation (QAM) has been described. The configuration of the present disclosure can be applied to an optical waveguide type light receiving element having a method of directly detecting an intensity modulated signal such as non-return-to-zero (NRZ) or 4-level pulse amplitude modulation (PAM4).

[0111] Fig.12 is a plan view illustrating an example of such an optical waveguide type light receiving element. Fig.12 The optical waveguide type light receiving element 2E illustrated in FIG. 1 includes a substrate 9 ( Fig.12 The substrate 9 is semi-insulating. The n-type semiconductor layer 10 is disposed on the substrate 9. The optical waveguide portion 8 and the light receiving element portion 6 are disposed on the n-type semiconductor layer 10. In the above-described embodiments and modifications, the optical waveguide portion 8 has an arbitrary optical waveguide structure 80. In the above-described embodiments and modifications, the light receiving element portion 6 has any one of the photodiode structures 19, 19B, 19C. In addition, the light receiving element 2E includes the above-described multiplication layer 11 and the n-type electric field control layer 12.

[0112] In this example, the electrode pad 23 and the wiring on the p-type ohmic electrode are electrically connected to each other via the wiring 71. The bias wiring provided on the n-type ohmic electrode is electrically connected to a pair of electrode pads 22e and 22f provided on both sides of the light receiving element portion 6. The configuration of this modified form can also exhibit effects similar to those of the aforementioned embodiment. In this example, it is possible to set Fig.11 The p-type semiconductor layer 101 is substituted for the n-type semiconductor layer 10, and the optical waveguide portion 8 may have Fig.11 The optical waveguide structure 180 is substituted for the optical waveguide structure 80, and the light receiving element portion 6 may have Fig.11 The photodiode structure 119 replaces the photodiode structure 19, 19B or 19C.

[0113] (Second embodiment)

[0114] A semiconductor light receiving element according to a second embodiment will be described. Fig.13 2F according to the second embodiment. In the light receiving device using the semiconductor light receiving element of the present embodiment, the light receiving element portion is provided on the substrate 9 independently of the optical waveguide portion. Fig.13, the light receiving element 2F does not include the optical waveguide structure 80 of the first embodiment. The light receiving element 2F has a configuration in which the photodiode structure 19 of the first embodiment is changed to a photodiode structure 19F. In addition, the light receiving element 2F includes a p-type semiconductor layer 87 (seventh semiconductor layer) provided adjacent to the photodiode structure 19F. The light receiving element 2F may have a configuration similar to that of the light receiving element 2A of the aforementioned embodiment except for the points to be described below.

[0115] Similar to the photodiode structure 19, the photodiode structure 19F has a light absorbing layer 13, a p-type semiconductor layer 14, and a p-type contact layer 15. The light absorbing layer 13 is of n-type conductivity type (first conductivity type) and is disposed on the n-type semiconductor layer 10. The p-type semiconductor layer 14 is disposed on the light absorbing layer 13 and is of p-type conductivity type (second conductivity type). The p-type contact layer 15 is disposed on the p-type semiconductor layer 14. In addition, the photodiode structure 19F has a multiplication layer 11 and an n-type electric field control layer 12. The multiplication layer 11 is disposed between the light absorbing layer 13 and the p-type semiconductor layer 14. The n-type electric field control layer 12 is disposed between the multiplication layer 11 and the light absorbing layer 13. The n-type semiconductor layer 10 is the first semiconductor layer according to the present embodiment. The n-type electric field control layer 12 is the second semiconductor layer according to the present embodiment. The p-type semiconductor layer 14 is the third semiconductor layer according to the present embodiment.

[0116] The light absorbing layer 13, the n-type electric field control layer 12, the multiplication layer 11, the p-type semiconductor layer 14 and the p-type contact layer 15 constitute a mesa structure extending in a predetermined direction (hereinafter referred to as the "optical axis direction"). The photodiode structure 19F has an end face 19b for allowing light to be incident thereon. In the mesa structure, the end face 19b is a surface that intersects the optical axis direction. The end face 19b is inclined relative to a direction perpendicular to the upper surface of the n-type semiconductor layer 10 (i.e., the interface between the n-type semiconductor layer 10 and the light absorbing layer 13). In other words, when the interface between the n-type semiconductor layer 10 and the photodiode structure 19F is the third interface C3, the angle θ formed by the end face 19b and the third interface C3 is less than 90°.

[0117] The p-type semiconductor layer 87 is of p-type conductivity type. The p-type semiconductor layer 87 has a greater refractive index than the n-type semiconductor layer 10 and is formed of a material that can undergo lattice matching with the n-type semiconductor layer 10. The band gap of the p-type semiconductor layer 87 is greater than the band gap of the light absorbing layer 13 and is equal to the band gap of the n-type semiconductor layer 10 or less than the band gap of the n-type semiconductor layer 10. For example, the material of the p-type semiconductor layer 87 is InGaAsP. As an example, the band gap wavelength of InGaAsP of the p-type semiconductor layer 87 is 1.05 μm. For example, the p-type semiconductor layer 87 is a Zn doping concentration of 3×10 16 cm -3The p-type semiconductor layer 87 has an impurity concentration lower than that of the p-type semiconductor layer 14 .

[0118] The p-type semiconductor layer 87 is disposed on the end surface 19b of the photodiode structure 19F and extends along the end surface 19b. The p-type semiconductor layer 87 rises on the end surface 19b of the photodiode structure 19F and contacts the light absorption layer 13, the n-type electric field control layer 12, the multiplication layer 11, and the p-type semiconductor layer 14 on the end surface 19b. For example, the thickness of the portion of the p-type semiconductor layer 87 adjacent to the multiplication layer 11 is in the range of 0.05 μm to 0.5 μm.

[0119] In the first embodiment described above, the light receiving element 2A in which the optical waveguide structure 80 and the photodiode structure 19 are integrated on the common substrate 9 has been described as an example. However, as in the light receiving element 2F according to the present embodiment, even in a configuration including the photodiode structure 19F provided separately on the substrate 9 from the optical waveguide structure 80, effects similar to those of the above first embodiment can be exhibited.

[0120] In addition, in the light receiving element 2F, similar to the photodiode structure 19 in the above-mentioned light receiving element 2A, the photodiode structure 19F includes a multiplication layer 11 and an n-type electric field control layer 12. The multiplication layer 11 is a carrier multiplication layer arranged between the p-type semiconductor layer 14 and the light absorption layer 13. The multiplication layer 11 is an n-type conductive type having an impurity concentration lower than that of the n-type semiconductor layer 10 or is an undoped layer. The n-type electric field control layer 12 is an electric field reducing layer arranged between the multiplication layer 11 and the light absorption layer 13 and is of an n-type conductive type. In this way, since the photodiode structure 19 includes the multiplication layer 11 and the n-type electric field control layer 12, a photodiode structure 19F having an avalanche multiplication effect can be obtained.

[0121] In addition, in the light receiving element 2F, the end face 19b of the photodiode structure 19F is inclined relative to the direction perpendicular to the main surface of the substrate 9. Therefore, the end face of the multiplication layer 11 is also inclined in a similar manner. For this reason, the length of the interface between the n-type electric field control layer 12 and the multiplication layer 11 in the optical waveguide direction becomes shorter than the length of the interface between the light absorption layer 13 and the multiplication layer 11 in the same direction. Therefore, if the p-type semiconductor layer 87 is not provided, when a reverse bias is applied, the negative charge in the portion near the end face of the multiplication layer 11 becomes insufficient, and depletion does not proceed compared to other portions in the multiplication layer 11. Therefore, the depletion range Ws of the portion near the end face of the multiplication layer 11 is narrowed compared to the depletion range Wc of other portions. As a result, edge breakdown is likely to occur at the end face 19b. In addition, the multiplication current is concentrated in the portion near the end face of the multiplication layer 11, and thus reliability deteriorates.

[0122] In the light receiving element 2F of the present embodiment, the p-type semiconductor layer 87 provided on the end face 19b is in contact with the multiplication layer 11 and the n-type electric field control layer 12 on the end face 19b. In this case, when a reverse bias is applied, the portion near the end face of the multiplication layer 11 is supplemented with carriers from the p-type semiconductor layer 87. This supplementation expands the depletion range near the end face of the multiplication layer 11. Therefore, in the multiplication layer 11, the depletion range becomes uniform from the central portion to the portion near the end face, and there is no non-uniformity in the depletion range caused by the inclination of the end face. That is, according to the light receiving element 2F of the present embodiment, the depletion range of the multiplication layer 11 can be made roughly uniform. Therefore, the local increase of the maximum electric field Emax in the multiplication layer 11 can be suppressed. As a result, edge breakdown can be made less likely to occur, and reliability degradation due to the concentration of the multiplication current can be avoided.

[0123] In this embodiment, the configuration in which the first conductivity type is n type and the second conductivity type is p type has been described as an example. However, even if the first conductivity type is p type and the second conductivity type is n type, effects similar to those of this embodiment can be exhibited.

[0124] The above-mentioned embodiments and modifications can be combined together when necessary according to the purpose and effect. The specific composition of each semiconductor layer is not limited to the above-mentioned example. In the above-mentioned example, the n-type semiconductor layer 10 is provided on the substrate 9. However, when the substrate is an n-type semiconductor substrate, the n-type semiconductor layer 10 can be omitted. In this case, the n-type semiconductor substrate becomes the first semiconductor layer, and all the relationships between the n-type semiconductor layer 10 and other semiconductor layers in the above-mentioned description can be understood as the relationship between the n-type semiconductor substrate and other semiconductor layers.

Claims

1. A semiconductor light receiving element, comprising: a first semiconductor layer of a first conductivity type; a waveguide photodiode structure having an end face disposed on the first semiconductor layer and comprising a light absorbing layer, a second semiconductor layer, a multiplication layer, and a third semiconductor layer, wherein the light absorbing layer is of an intrinsic conductivity type or a first conductivity type, the second semiconductor layer is of a first conductivity type, the multiplication layer is of an intrinsic conductivity type or a first conductivity type, and the third semiconductor layer is of a second conductivity type; an optical waveguide structure having an end face disposed on the first semiconductor layer and comprising an optical waveguide core layer and a cladding layer, the end face of the waveguide type photodiode structure facing the end face of the optical waveguide structure; as well as A fourth semiconductor layer, the fourth semiconductor layer is of the second conductivity type, the fourth semiconductor layer is located between the end face of the waveguide photodiode structure and the end face of the optical waveguide structure, and is in contact with the multiplication layer of the end face of the waveguide photodiode structure.

2. The semiconductor light receiving element according to claim 1, in, The impurity concentration of the fourth semiconductor layer is lower than the impurity concentration of the third semiconductor layer.

3. The semiconductor light receiving element according to claim 1 or 2, further comprising: a fifth semiconductor layer, the fifth semiconductor layer being disposed between the first semiconductor layer and the light absorbing layer, The fifth semiconductor layer is of the first conductivity type with a lower impurity concentration than the first semiconductor layer, and extends between the first semiconductor layer and the optical waveguide core layer.

4. The semiconductor light receiving element according to claim 1 or 2, in, The waveguide type photodiode structure further includes a sixth semiconductor layer disposed between the first semiconductor layer and the light absorbing layer and having a first conductivity type with a lower impurity concentration than that of the first semiconductor layer.

5. The semiconductor light receiving element according to claim 1 or 2, further comprising: a semiconductor passivation film, wherein the semiconductor passivation film is arranged in the waveguide type photodiode structure, wherein, in the waveguide type photodiode structure, the light absorption layer, the second semiconductor layer, the multiplication layer and the third semiconductor layer constitute a striped mesa structure, and the striped mesa structure extends in a first direction which is an arrangement direction of the waveguide type photodiode structure and the optical waveguide structure, The striped mesa structure has a pair of side surfaces extending in the first direction, and Wherein, the semiconductor passivation film is in contact with the pair of side surfaces.

6. The semiconductor light receiving element according to claim 1 or 2, in, The impurity concentration of the fourth semiconductor layer is 3×10 16 cm -3 or lower.

7. The semiconductor light receiving element according to claim 1 or 2, in, The band gap of the fourth semiconductor layer is larger than the band gap of the light absorbing layer, and is equal to or smaller than the band gap of the first semiconductor layer.

8. The semiconductor light receiving element according to claim 1 or 2, in, An angle between the end face of the waveguide photodiode structure and a plane of the first semiconductor layer is less than 90°.

9. The semiconductor light receiving element according to claim 1 or 2, further comprising: a contact layer of a second conductivity type, wherein the contact layer is disposed on the third semiconductor layer; a first ohmic electrode, wherein the first ohmic electrode is disposed on the contact layer; as well as A second ohmic electrode is disposed on the first semiconductor layer outside the waveguide photodiode structure.

10. The semiconductor light receiving element according to claim 1 or 2, further comprising: Semi-insulating substrate, Wherein, the first semiconductor layer is arranged on the semi-insulating substrate.

11. The semiconductor light receiving element according to claim 1 or 2, in, The band gap of the fourth semiconductor layer is equal to the band gap of the optical waveguide core layer.

12. The semiconductor light receiving element according to claim 1 or 2, in, The first semiconductor layer, the multiplication layer and the third semiconductor layer are InP layers, Wherein, the light absorbing layer is an InGaAs layer, Wherein, the second semiconductor layer is an InP layer or an InAlGaAs layer, and Wherein, the fourth semiconductor layer is an InGaAsP layer.

13. The semiconductor light receiving element according to claim 1 or 2, in, The fourth semiconductor layer has a thickness in the range of 0.050 μm to 0.200 μm.

14. A semiconductor light receiving element, comprising: An n-type first semiconductor layer; a photodiode structure, the photodiode structure being disposed on the first semiconductor layer, the photodiode structure having an end face, the photodiode structure comprising a light absorbing layer, a second semiconductor layer, a multiplication layer and a third semiconductor layer, the light absorbing layer being of an intrinsic conductivity type or an n-type, the second semiconductor layer being of an n-type, the multiplication layer being of an intrinsic conductivity type or an n-type, and the third semiconductor layer being of a p-type; as well as a seventh semiconductor layer, the seventh semiconductor layer being of p-type and contacting the multiplication layer on the end face of the photodiode structure, An angle formed by an end face of the multiplication layer and an interface between the first semiconductor layer and the multiplication layer is smaller than 90°.

15. The semiconductor light receiving element according to claim 14, in, The impurity concentration of the seventh semiconductor layer is lower than the impurity concentration of the third semiconductor layer.

16. The semiconductor light receiving element according to claim 14 or 15, in, The impurity concentration of the seventh semiconductor layer is 3×10 16 cm -3 or lower.

17. The semiconductor light receiving element according to claim 14 or 15, in, The band gap of the seventh semiconductor layer is larger than the band gap of the light absorbing layer, and is equal to or smaller than the band gap of the first semiconductor layer.

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