Semiconductor light receiving element

Abstract

This semiconductor light-receiving element (1) is provided with a substrate, and a semiconductor laminated part (20) that is formed on the substrate and includes a back surface on the substrate side, a surface on the opposite side from the substrate, and a side surface (20s) that extends from the back surface toward the surface. The semiconductor laminated part (20) comprises a light absorption layer (23) of a first conductivity type containing InxGa1-xAs, a buffer layer of the first conductivity type provided between the substrate and the light absorption layer (23), and a light absorption layer (23) located on the opposite side of the substrate with respect to the light absorption layer (23). In the semiconductor light receiving element, the In composition x in the light absorbing layer (23) is 0.55 or more, the thickness of the light absorbing layer (23) is 1.8 [mu] m or less, and the semiconductor light receiving element is of a side surface incidence type in which the incident light is received from the side surface (20s), and is of a first semiconductor layer (24, 25) of a second conductivity type which is different from the first conductivity type, the In composition x in the light absorbing layer (23) is 0.55 or more, and the thickness of the light absorbing layer (23) is 1.8 [mu] m or less. The width of the light absorbing layer (23) along the incident direction of the light to the side surface (20s) is 10 [mu] m or less.

Description

Technical Field

[0001] The present disclosure relates to a semiconductor light-receiving element. Background Art

[0002] Patent document 1 describes an optical waveguide type photosensitive element. The optical waveguide type photosensitive element comprises a first semiconductor layer having a first conductivity type, an optical waveguide structure disposed on a first region of the first semiconductor layer, and a waveguide type photodiode structure disposed on a second region of the first semiconductor layer adjacent to the first region. The optical waveguide structure comprises an optical waveguide core layer disposed on the first semiconductor layer, and a cladding layer disposed on the optical waveguide core layer. The waveguide type photodiode structure comprises an optical absorption layer disposed on the first semiconductor layer, optically coupled with the optical waveguide core layer, and having an absorption end wavelength of 1612 nm or more, and a second semiconductor layer having a second conductivity type disposed on the optical absorption layer. The length of the optical absorption layer in the optical waveguide direction is 12 μm or more.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2009-117499 Summary of the invention

[0006] Problems to be solved by the invention

[0007] However, in the above-mentioned technical field, it is desired to increase the speed of operation. Therefore, it is considered to shorten the moving distance of electrons by thinning the light absorbing layer. However, if the light absorbing layer is thinned, the sensitivity is reduced. In contrast, in the photodiode described in Patent Document 1, the thickness of the absorption layer is increased by incident light on the light absorbing layer from a direction intersecting the thickness direction of the light absorbing layer (the light absorbing layer has a length of 12 μm in the optical waveguide direction). Based on this, it is also considered to suppress the reduction in sensitivity caused by the thinning of the light absorbing layer and achieve high speed. In this way, there is a demand for high speed in the above-mentioned technical field.

[0008] An object of the present disclosure is to provide a semiconductor light-receiving element capable of increasing speed.

[0009] Technical solutions to solve problems

[0010] The semiconductor light receiving element disclosed in the present invention is [1] "a semiconductor light receiving element for receiving incident light of at least one of the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band, and generating an electrical signal according to the incident light, wherein the semiconductor light receiving element comprises: a substrate; a semiconductor stacking portion formed on the substrate, comprising a back surface on the substrate side, a surface on the opposite side of the substrate, and a side surface extending from the back surface toward the surface; and a first electrode and a second electrode electrically connected to the semiconductor stacking portion, wherein the semiconductor stacking portion comprises: a first conductivity type light absorption layer comprising In x Ga 1-x As; a buffer layer of the first conductivity type, which is arranged between the substrate and the light absorbing layer; and a first semiconductor layer of a second conductivity type different from the first conductivity type, which is located on the opposite side of the substrate relative to the light absorbing layer and is bonded to the light absorbing layer, the first electrode is connected to a first portion of the first conductivity type in the semiconductor stack portion, which is located on the substrate side relative to the light absorbing layer, and the second electrode is connected to a second portion of the second conductivity type in the semiconductor stack portion, which is located on the opposite side of the substrate relative to the light absorbing layer, the In composition x in the light absorbing layer is greater than 0.55, the thickness of the light absorbing layer is less than 1.8μm, the semiconductor light receiving element is a side-incident type that receives the incident light from the side, and the width of the light absorbing layer along the incident direction of the light relative to the side is less than 10μm.

[0011] The semiconductor light-receiving element of [1] is for receiving light in the wavelength bands used for optical communication such as the 1.3 μm band (O-band (Original-band)), the 1.55 μm band (C-band (Conventional-band)), and the 1.6 μm band (L-band (Long-wavelength-band)). In the semiconductor light-receiving element, the light absorption layer provided on the substrate includes In x Ga 1-x As. Moreover, the In composition x of the light absorbing layer is greater than 0.55 (and less than 1). x Ga 1-xWhen the In composition x of As is set to 0.55 or more, for example, compared with the case where the In composition x is 0.53, the absorption coefficient is increased (for example, by setting the composition x to 0.62 in the 1.55μm band, the absorption coefficient is increased to about 2 times). Therefore, even if the thickness of the light absorption layer is thinned to about 1.8μm or less, the sensitivity can be avoided from being reduced. Therefore, the speed can be increased. Furthermore, for the same reason, the width of the light absorption layer in the incident direction of light can be set to 10μm or less, which can reduce the capacitance of the light absorption layer and achieve further speed increase.

[0012] The semiconductor light-receiving element of the present disclosure may also be, [2] "a semiconductor light-receiving element according to [1], wherein the buffer layer includes a strain relaxation layer having a lattice constant between the lattice constant of the substrate and the lattice constant of the light-absorbing layer". In this case, the crystallinity of the semiconductor stack is improved, and the increase of dark current is suppressed.

[0013] The semiconductor light-receiving element of the present invention may also be, [3] "According to the semiconductor light-receiving element described in [2], wherein the buffer layer includes a plurality of strain relief layers, and the plurality of strain relief layers are configured so that the lattice constant gradually approaches the lattice constant of the light-absorbing layer as it moves from the substrate toward the light-absorbing layer". Alternatively, the semiconductor light-receiving element of the present invention may also be, [4] "According to the semiconductor light-receiving element described in [2], wherein the buffer layer includes a strain relief layer, and the strain relief layer changes so that the lattice constant continuously approaches the lattice constant of the light-absorbing layer as it moves from the substrate toward the light-absorbing layer". In these cases, the crystallinity of the semiconductor stack portion is reliably improved, and the increase in dark current is suppressed.

[0014] The semiconductor light-receiving element disclosed in the present invention may also be, [5] "a semiconductor light-receiving element according to any one of [1] to [4], wherein the semiconductor stack portion includes: a cap layer of the second conductivity type, which is arranged on the light-absorbing layer on the opposite side of the substrate relative to the light-absorbing layer and includes InAsP or InGaAsP; and a contact layer of the second conductivity type, which is arranged on the cap layer on the opposite side of the substrate relative to the light-absorbing layer and includes InGaAs, the first semiconductor layer includes the contact layer and the cap layer, and the second portion connected to the second electrode is the surface of the contact layer". In this case, the contact resistance of the second electrode can be reduced, and the series resistance can be reduced. Thus, the deterioration of the responsiveness can be suppressed. In addition, by using a material with a refractive index lower than that of the light-absorbing layer as the cap layer, light can be appropriately confined in the light-absorbing layer.

[0015] The semiconductor light-receiving element disclosed in the present invention may also be, [6] "a semiconductor light-receiving element according to any one of [1] to [5], wherein the semiconductor stack portion includes: a second semiconductor layer of the first conductivity type, which is arranged between the optical waveguide layer and the light absorption layer; and a capacitance-reducing layer of the first conductivity type, which has an impurity concentration lower than the impurity concentration of the second semiconductor layer, and is arranged between the second semiconductor layer and the light absorption layer". In this way, by providing a capacitance-reducing layer with a relatively low impurity concentration, the capacitance-reducing layer is depleted when a bias voltage is applied, thereby achieving further speed increase by reducing the capacitance.

[0016] The semiconductor light-receiving element of the present disclosure may also be, [7] "the semiconductor light-receiving element according to [5], wherein the semiconductor stack portion includes a third semiconductor layer, the third semiconductor layer is provided between the light-absorbing layer and the cap layer, and has a band gap between the band gap of the light-absorbing layer and the band gap of the cap layer". In this case, by providing a layer having a band gap between the light-absorbing layer and the cap layer, the potential barrier between the layers can be reduced, and the degradation of the response can be suppressed.

[0017] The semiconductor light-receiving element of the present disclosure may also be [8] "the semiconductor light-receiving element according to any one of [1] to [7], wherein at least one of the buffer layers is semi-insulated by Fe doping". In this case, the capacitance can be reduced.

[0018] The semiconductor light-receiving element of the present disclosure may also be, [9] "the semiconductor light-receiving element according to the above [6], wherein the capacitance-reducing layer is provided between the light-absorbing layer and the optical waveguide layer, has an impurity concentration higher than that of the light-absorbing layer, and has a band gap larger than that of the light-absorbing layer". In this case, the capacitance-reducing layer is a layer having a relatively low impurity concentration as described above and contributing to capacitance reduction. However, if only the impurity concentration of the capacitance-reducing layer is reduced, the potential barrier between the layers becomes larger, which may lead to degradation of the response. On the other hand, if the impurity concentration of the capacitance-reducing layer is increased, the depletion layer cannot be widened, and therefore it is difficult to sufficiently reduce the capacitance. Therefore, by reducing the impurity concentration of the capacitance-reducing layer to the minimum as in this case, the capacitance-reducing layer has a larger band gap than the light-absorbing layer, and the absorption of light in the capacitance-reducing layer and the generation of carriers in the capacitance-reducing layer caused by the absorption of light are suppressed, thereby suppressing the degradation of the response. In addition, since the capacitance-reducing layer has a larger band gap than the light-absorbing layer and, on the other hand, the capacitance-reducing layer has a higher impurity concentration than the light-absorbing layer, the potential barrier in the capacitance-reducing layer is reduced.

[0019] The semiconductor light-receiving element of the present disclosure may also be,

[10] “the semiconductor light-receiving element according to [6] or [9], wherein the thickness of the capacitance-reducing layer is 0.3 μm or more and 3.0 μm or less, and the impurity concentration of the capacitance-reducing layer is 2.0×10 14 cm -3 Above and 3.0×10 16 cm -3 In this case, by setting the upper limit of the impurity concentration of the capacitance reducing layer as described above, it can be appropriately depleted when a bias voltage is applied. In addition, by setting the thickness of the capacitance reducing layer to the above range, a decrease in response speed and an increase in series resistance of the semiconductor light receiving element can be suppressed.

[0020] The semiconductor light receiving element of the present disclosure may also be,

[11] "a semiconductor light receiving element according to any one of [1] to

[10] , wherein the In composition x in the light absorbing layer is greater than 0.57, and the thickness of the light absorbing layer is less than 1.2 μm". Furthermore, the semiconductor light receiving element of the present disclosure may also be,

[12] "a semiconductor light receiving element according to

[11] , wherein the In composition x in the light absorbing layer is greater than 0.59, and the thickness of the light absorbing layer is less than 0.7 μm". In these cases, high speed is achieved by further thinning the light absorbing layer.

[0021] The semiconductor light-receiving element of the present disclosure may also be,

[13] "a semiconductor light-receiving element according to any one of [1] to

[12] , wherein the substrate includes a semi-insulating semiconductor". In this case, by providing a pad for the first electrode on the substrate, the pad capacitance can be reduced, and the speed can be increased.

[0022] The semiconductor light-receiving element disclosed in the present invention may also be,

[14] "a semiconductor light-receiving element according to any one of [1] to

[13] , wherein the substrate comprises an insulator or a semi-insulating semiconductor, and the semiconductor stack portion is bonded to the substrate". In this case, by forming the substrate and the semiconductor stack portion separately and forming the semiconductor light-receiving element by direct bonding, it is possible to achieve a larger aperture and suppress costs by using inexpensive materials to make optical parts.

[0023] The semiconductor light receiving element disclosed in the present invention is

[15] "a semiconductor light receiving element for receiving incident light of at least one of the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band, and generating an electrical signal according to the incident light, wherein the semiconductor light receiving element comprises: a substrate; a semiconductor stacking portion formed on the substrate, including a back surface on the substrate side, a surface on the opposite side of the substrate, and a side surface extending from the back surface toward the surface; and a first electrode and a second electrode electrically connected to the semiconductor stacking portion, wherein the semiconductor stacking portion comprises: a second conductivity type light absorption layer including In x Ga 1-x As; a buffer layer of a first conductivity type, which is arranged between the substrate and the light absorbing layer and is different from the second conductivity type; and a fourth semiconductor layer of the second conductivity type, which is located on the opposite side of the substrate relative to the light absorbing layer and is bonded to the light absorbing layer, the first electrode is connected to a first portion of the first conductivity type in the semiconductor stack portion, which is located on the substrate side relative to the light absorbing layer, and the second electrode is connected to a second portion of the second conductivity type in the semiconductor stack portion, which is located on the opposite side of the substrate relative to the light absorbing layer, the In composition x in the light absorbing layer is greater than 0.55, the thickness of the light absorbing layer is less than 1.8μm, the semiconductor light receiving element is a side-incident type that receives the incident light from the side, and the width of the light absorbing layer along the incident direction of the light relative to the side is less than 10μm.

[0024] The semiconductor light-receiving element of

[15] is targeted at light in the wavelength band used for optical communication, such as the 1.3 μm band (O-band (Original-band)), the 1.55 μm band (C-band (Conventional-band)), and the 1.6 μm band (L-band (Long-wavelength-band)). In the semiconductor light-receiving element, the light absorption layer provided on the substrate includes In x Ga 1- x As. Moreover, the In composition x of the light absorbing layer is greater than 0.55 (and less than 1). x Ga 1-xWhen the In composition x of As is set to 0.55 or more, for example, the absorption coefficient is increased compared to the case where the In composition x is 0.53 (for example, by setting the composition x to 0.62 in the 1.55 μm band, the absorption coefficient is increased to about 2 times). Therefore, even if the thickness of the light absorption layer is thinned to about 1.8 μm or less, the sensitivity can be avoided from being reduced. Furthermore, for the same reason, the width of the light absorption layer in the incident direction of light can be set to 10 μm or less, which can reduce the capacitance of the light absorption layer and achieve further high speed.

[0025] The semiconductor light-receiving element of the present disclosure may also be,

[16] "a semiconductor light-receiving element according to

[15] , wherein the buffer layer includes a strain relaxation layer having a lattice constant between the lattice constant of the substrate and the lattice constant of the light-absorbing layer". In this case, the crystallinity of the semiconductor stack is improved, and the increase of dark current is suppressed.

[0026] The semiconductor light-receiving element of the present invention may also be,

[17] "According to the semiconductor light-receiving element described in

[16] , wherein the buffer layer includes a plurality of strain relief layers, and the plurality of strain relief layers are configured so that the lattice constant gradually approaches the lattice constant of the light-absorbing layer as it moves from the substrate toward the light-absorbing layer". Alternatively, the semiconductor light-receiving element of the present invention may also be,

[18] "According to the semiconductor light-receiving element described in

[16] , wherein the buffer layer includes a strain relief layer, and the strain relief layer changes so that the lattice constant continuously approaches the lattice constant of the light-absorbing layer as it moves from the substrate toward the light-absorbing layer". In these cases, the crystallinity of the semiconductor stack portion is reliably improved, and the increase of dark current is suppressed.

[0027] The semiconductor light-receiving element disclosed in the present invention may also be,

[19] "a semiconductor light-receiving element according to any one of

[15] to

[18] , wherein the semiconductor stack portion includes: a diffusion barrier layer of the second conductivity type, which is arranged on the light-absorbing layer on the opposite side of the substrate relative to the light-absorbing layer and includes InAsP or InGaAsP; and a contact layer of the second conductivity type, which is arranged on the diffusion barrier layer on the opposite side of the substrate relative to the light-absorbing layer and includes InGaAs, the fourth semiconductor layer includes the contact layer and the diffusion barrier layer, and the second portion connected to the second electrode is the surface of the contact layer". In this case, the contact resistance of the second electrode can be reduced, and the series resistance can be reduced. Thus, the deterioration of the responsiveness can be suppressed. In addition, by using a material with a refractive index lower than that of the light-absorbing layer as the diffusion barrier layer, light can be appropriately confined in the light-absorbing layer.

[0028] The semiconductor light-receiving element disclosed in the present invention may also be,

[20] "a semiconductor light-receiving element according to any one of

[15] to

[19] , wherein the semiconductor stack portion includes an electron transport layer of a first conductivity type arranged between the buffer layer and the light-absorbing layer, and the impurity concentration of the electron transport layer is lower than the impurity concentration of the buffer layer". In this way, by relatively reducing the impurity concentration of the electron transport layer, the electron transport layer is depleted when a bias voltage is applied, thereby achieving further speed increase by reducing the capacitance.

[0029] The semiconductor light-receiving element of the present disclosure may also be,

[21] "the semiconductor light-receiving element according to

[19] , wherein the semiconductor stack portion includes a sixth semiconductor layer, the sixth semiconductor layer is provided between the light-absorbing layer and the diffusion barrier layer, and has a band gap between the band gap of the light-absorbing layer and the band gap of the diffusion barrier layer". In this case, by providing a layer having a band gap between the light-absorbing layer and the cap layer, the potential barrier between the layers can be reduced and the degradation of the response can be suppressed.

[0030] The semiconductor light-receiving element of the present disclosure may also be

[22] "a semiconductor light-receiving element according to any one of

[15] to

[21] , wherein at least one of the buffer layers includes a layer semi-insulated by Fe doping". In this case, the capacitance can be reduced.

[0031] The semiconductor light-receiving element disclosed in the present invention may also be,

[23] "according to the semiconductor light-receiving element described in

[20] , wherein the electron transport layer is arranged between the light-absorbing layer and the optical waveguide layer, has an impurity concentration lower than the impurity concentration of the light-absorbing layer, and has a band gap larger than the band gap of the light-absorbing layer". In this case, by relatively reducing the impurity concentration of the electron transport layer, it is possible to reduce the capacitance. In addition, by reducing the impurity concentration of the electron transport layer, it is easy to deplete it, and it is also possible to reduce the potential barrier between it and the light-absorbing layer.

[0032] The semiconductor light-receiving element of the present disclosure may also be,

[24] "the semiconductor light-receiving element according to

[20] or

[23] , wherein the thickness of the electron transport layer is 0.3 μm or more and 3.0 μm or less, and the impurity concentration of the electron transport layer is 2.0×10 14 cm -3 Above and 3.0×10 16 cm -3 In this case, by setting the upper limit of the impurity concentration of the electron transport layer as described above, it can be appropriately depleted when a bias voltage is applied. In addition, by setting the thickness of the electron transport layer to the range described above, a decrease in response speed and an increase in series resistance of the semiconductor light-receiving element can be suppressed.

[0033] The semiconductor light receiving element of the present invention may also be,

[25] "a semiconductor light receiving element according to any one of

[15] to

[24] , wherein the In composition x in the light absorbing layer is greater than 0.57, and the thickness of the light absorbing layer is less than 0.3 μm". Furthermore, the semiconductor light receiving element of the present invention may also be,

[26] "a semiconductor light receiving element according to any one of

[15] to

[25] , wherein the In composition x in the light absorbing layer is greater than 0.59, and the thickness of the light absorbing layer is less than 0.1 μm". In these cases, high speed is achieved by further thinning the light absorbing layer.

[0034] The semiconductor light-receiving element disclosed in the present invention may also be,

[27] "a semiconductor light-receiving element according to any one of

[15] to

[26] , wherein the substrate includes a semi-insulating semiconductor". In this case, by providing a pad for the first electrode on the substrate, the pad capacitance can be reduced, and the speed can be increased.

[0035] The semiconductor light-receiving element disclosed in the present invention may also be,

[28] "a semiconductor light-receiving element according to any one of

[15] to

[27] , wherein the substrate comprises an insulator or a semi-insulating semiconductor, and the semiconductor stack portion is bonded to the substrate". In this case, by forming the substrate and the semiconductor stack portion separately and forming the semiconductor light-receiving element by direct bonding, it is possible to achieve a larger aperture and suppress costs by using inexpensive materials to make optical parts.

[0036] The semiconductor light receiving element disclosed in the present invention is

[29] "a semiconductor light receiving element for receiving incident light of at least one of the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band, and generating an electrical signal according to the incident light, wherein the semiconductor light receiving element comprises: a substrate having a main surface including a first region, a second region, and a third region arranged in sequence along a first direction; a semiconductor stack portion formed on the second region, including a back surface on the substrate side, a surface on the opposite side of the substrate, and a side surface extending from the back surface toward the surface; a first semiconductor portion of a first conductivity type formed on the first region; a second semiconductor portion of a second conductivity type formed on the third region and different from the first conductivity type; a first electrode electrically connected to the first semiconductor portion; a second electrode electrically connected to the second semiconductor portion; and an optical waveguide formed on the second region, extending toward the side surface along a second direction and coupled to the side surface, the second direction being along the main surface and intersecting the first direction, the semiconductor stack portion including a light absorbing layer, the light absorbing layer including In x Ga 1-xAs, the In composition x in the light absorbing layer is greater than or equal to 0.55, the thickness of the light absorbing layer is less than or equal to 1.8 μm, the semiconductor light receiving element is a side-incident type that receives the incident light from the side via the optical waveguide, and the width of the light absorbing layer along the incident direction of the light relative to the side is less than or equal to 10 μm.

[0037] The semiconductor light-receiving element of

[29] is targeted at light in the wavelength bands used for optical communication such as the 1.3 μm band (O-band (Original-band)), the 1.55 μm band (C-band (Conventional-band)), and the 1.6 μm band (L-band (Long-wavelength-band)). In the semiconductor light-receiving element, the light absorption layer provided on the substrate includes In x Ga 1- x As. Moreover, the In composition x of the light absorbing layer is greater than 0.55 (and less than 1). x Ga 1-x When the In composition x of As is set to 0.55 or more, for example, the absorption coefficient is increased compared to the case where the In composition x is 0.53 (for example, by setting the composition x to 0.62 in the 1.55 μm band, the absorption coefficient is increased to about 2 times). Therefore, even if the thickness of the light absorption layer is thinned to about 1.8 μm or less, the sensitivity can be avoided from being reduced. Furthermore, for the same reason, the width of the light absorption layer in the incident direction of light can be set to 10 μm or less, which can reduce the capacitance of the light absorption layer and achieve further high speed.

[0038] Effects of the Invention

[0039] According to the present disclosure, it is possible to provide a semiconductor light-receiving element capable of increasing speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 It is a schematic plan view showing the semiconductor light-receiving element according to the first embodiment.

[0041] Figure 2 It is along Figure 1 A schematic cross-sectional view taken along line II-II.

[0042] Figure 3 It is along Figure 1 Schematic cross-sectional view along line III-III.

[0043] Figure 4 This is a graph illustrating the relationship between the composition of the light absorbing layer and the absorption coefficient.

[0044] Figure 5It is a schematic cross-sectional view of a semiconductor light-receiving element according to the second embodiment.

[0045] Figure 6 It is a schematic cross-sectional view of a semiconductor light-receiving element according to a third embodiment.

[0046] Figure 7 It is a schematic cross-sectional view of a semiconductor light-receiving element according to a fourth embodiment.

[0047] Figure 8 It is a schematic cross-sectional view of a semiconductor light-receiving element according to a fifth embodiment.

[0048] Fig. 9 It is a schematic top view of the semiconductor light receiving element according to the sixth embodiment.

[0049] Fig.10 It is along Fig. 9 A schematic cross-sectional view along line XX.

[0050] Fig.11 It is along Fig. 9 A schematic cross-sectional view taken along line XI-XI.

[0051] Fig.12 Yes means Fig.11 A cross-sectional view of a modified example of the semiconductor light-receiving element shown.

[0052] Fig.13 It is a schematic cross-sectional view of a semiconductor light-receiving element according to the seventh embodiment.

[0053] Fig.14 It is a schematic cross-sectional view of a semiconductor light-receiving element according to the seventh embodiment. DETAILED DESCRIPTION

[0054] Hereinafter, one embodiment will be described in detail with reference to the drawings. In addition, in each figure, the same reference numerals are attached to the same or corresponding elements, and overlapping descriptions may be omitted.

[0055] [First embodiment]

[0056] Figure 1 It is a schematic plan view showing the semiconductor light-receiving element according to the first embodiment. Figure 2 It is along Figure 1 A schematic cross-sectional view taken along line II-II. Figure 3 It is along Figure 1 Schematic cross-sectional view along line III-III. Figures 1 to 3The semiconductor photosensitive element 1 shown targets light in wavelength bands used for optical communications, such as the 1.3μm band (O-band (Original-band)), the 1.55μm band (C-band (Conventional-band)), and the 1.6μm band (L-band (Long-wavelength-band)). That is, the semiconductor photosensitive element 1 is used to receive the incidence of light in at least one of the above-mentioned multiple bands, and generate an electrical signal based on the incident light. The 1.3μm band is, for example, a wavelength range of greater than 1.26μm and less than 1.36μm. The 1.55μm band is, for example, a wavelength range of greater than 1.53μm and less than 1.565μm. The 1.6μm band is, for example, a wavelength range of less than 1.625μm, which is larger than 1.565μm. In addition, light in the wavelength band used for communication is light having a peak within the wavelength range of any of the above-mentioned bands (that is, wavelengths other than the peak may be outside the wavelength range of the above-mentioned bands).

[0057] The semiconductor light receiving element 1 includes a substrate 10, a semiconductor stacked portion 20, an electrode 4 (second electrode), and a pair of electrodes 5 (first electrodes). The electrode 4 includes a joint portion 4a joined to the semiconductor stacked portion 20, a pad portion 4b, and a connection portion 4c connecting the joint portion 4a and the pad portion 4b. The connection portion 4c widens from the joint portion 4a toward the pad portion 4b. The electrode 5 includes a joint portion 5a joined to the semiconductor stacked portion 20, a pad portion 5b, and a connection portion 5c connecting the joint portion 5a and the pad portion 5b. The connection portion 5c widens from the joint portion 5a toward the pad portion 5b.

[0058] The substrate 10 includes a semi-insulating semiconductor. Here, the substrate 10 is, for example, a semi-insulating semiconductor substrate composed of InP. The substrate 10 includes a surface (main surface) 10a and a back surface 10b on the opposite side of the surface 10a. In addition, the substrate 10 includes a region RA, a region RB, and a region RC arranged in sequence along the X-axis direction (first direction) according to the surface 10a and the back surface 10b. The region RB is a region between the region RA and the region RC, and is a region where the semiconductor stacking portion 20 is provided.

[0059] As described above, the semiconductor stack portion 20 is formed on the region RB of the substrate 10, and becomes a semiconductor table protruding from the surface 10a. The semiconductor stack portion 20 includes a back side 20b on the substrate 10 side, a surface 20a on the opposite side of the substrate 10, and a side 20s extending from the back side 20b toward the surface 20a. The side 20s connects the back side 20b and the surface 20a. The semiconductor stack portion 20 includes a buffer layer 21, a capacitance reduction layer 22, a light absorption layer 23, a cap layer 24 (first semiconductor layer), and a contact layer 25 (first semiconductor layer) stacked in sequence from the substrate 10 side. The surface 20a is the surface on the opposite side of the light absorption layer 23 of the contact layer 25, and the back side 20b is the surface on the opposite side of the light absorption layer 23 of the buffer layer 21, and contacts the surface 10a of the substrate 10.

[0060] The buffer layer 21 has a first conductivity type (here, N type, as an example, N + The buffer layer 21 is provided in the region RA and the region RC with the region RB as the center. Here, the semiconductor stack portion 20 is in contact with the surface 10a of the substrate 10 at the buffer layer 21. The layers other than the buffer layer 21 of the semiconductor stack portion 20 are provided on the region RB. That is, the buffer layer 21 has a portion 21p protruding from other layers of the semiconductor stack portion 20 when viewed from a direction intersecting the surface 10a, and a junction with the electrode 5 (junction 5a) is formed in the portion 21p.

[0061] The buffer layer 21 includes a first buffer layer, a second buffer layer, and a third buffer layer stacked in order from the substrate 10 side. As an example, the first buffer layer is composed of N + -InP, the second buffer layer is composed of N + -InAs 0.05 P, the third buffer layer is composed of N + -InAs 0.10 The capacitance reducing layer 22 has a first conductivity type (here, N type, as an example, N - Type), as an example, by N - -InAs 0.15 P composition.

[0062] Thus, the buffer layer 21 and the capacitance reduction layer 22 function as strain relaxation layers having a lattice constant between the lattice constant of the substrate 10 and the lattice constant of the light absorption layer 23. That is, the semiconductor stacked portion 20 includes a plurality of strain relaxation layers (step layers) provided so that the lattice constant gradually approaches the lattice constant of the light absorption layer 23 as it moves from the substrate 10 toward the light absorption layer 23. The thickness of the buffer layer 21 is, for example, not less than 0.5 μm and not more than 5 μm.

[0063] The capacitance reduction layer 22 is disposed on the light absorbing layer 23 side of the buffer layer 21 and has an impurity concentration lower than that of the buffer layer 21. The light absorbing layer 23 has a first conductivity type (eg, N - The light absorbing layer 23 includes InGaAs. Here, the light absorbing layer 23 is composed of N - -In x Ga 1-x As. The In composition x of the light absorbing layer 23 is 0.55 or more (and less than 1). As an example, the In composition x may be 0.57 or more, and is 0.59 or more (0.59 as an example) in this example.

[0064] In addition, the thickness of the light absorption layer 23 (the thickness along the stacking direction (Z-axis direction) of the semiconductor stacking portion 20) is greater than or equal to 0.6 μm and less than or equal to 1.8 μm. As an example, the thickness of the light absorption layer 23 may be less than or equal to 1.2 μm, and is less than or equal to 0.7 μm (0.7 μm as an example). In addition, the light absorption layer 23 may be an absorption layer of a mixed crystal of Al, P, Sb, N, other materials, and InGaAs within a band gap range of less than or equal to 0.72 eV. The proportion of Al, P, Sb, and N (or other materials) mixed in InGaAs can be set to, for example, less than or equal to 5% or less than or equal to 10%.

[0065] Here, the capacitance reduction layer 22 has an impurity concentration higher than the impurity concentration of the light absorbing layer 23. As an example, the impurity concentration of the capacitance reduction layer 22 is 2.0×10 14 cm -3 Above and 3.0×10 16 cm -3 The impurity concentration of the light absorbing layer 23 is 1.0×10 14 cm -3 Above and 1.0×10 16 cm -3 Furthermore, the capacitance reducing layer 22 has a band gap larger than the band gap of the light absorbing layer 23. As described above, when the band gap of the light absorbing layer 23 is 0.72 eV or less, the band gap of the capacitance reducing layer 22 can be set to a range larger than 0.72 eV and 1.35 eV or less.

[0066] Thus, the semiconductor stacked portion 20 has a capacitance reduction layer 22 disposed between the buffer layer 21 and the light absorbing layer 23. The capacitance reduction layer 22 is required to have a higher impurity concentration than the light absorbing layer 23 and to be depleted when a bias is applied, as described above. The reason for this is that, as described above, the capacitance reduction layer 22 has a larger band gap than the light absorbing layer 23, and therefore, when the impurity concentration is low, a potential barrier is formed in the conduction band, and the movement of carriers with a large potential barrier is hindered, and it may not be properly extracted.

[0067] In addition, since the capacitance reducing layer 22 needs to be depleted when a bias voltage is applied, the upper limit of the impurity concentration can be set to 3.0×10 16 cm -3 Furthermore, as the capacitance reduction layer 22, it is desirable to have a composition that does not absorb incident light (that is, the band gap is wider than that of the light absorbing layer 23). This is because if the capacitance reduction layer 22 absorbs incident light, carriers are generated in the capacitance reduction layer 22. The carriers are taken out as signals from the capacitance reduction layer 22 via the light absorbing layer 23, and therefore become slow carriers, which may deteriorate the responsiveness characteristics.

[0068] In other words, by setting the relationship between the buffer layer 21, the capacitance reducing layer 22, and the light absorbing layer 23 as described above, the capacitance reducing layer 22 can function as a layer that can reduce capacitance without reducing the response of carriers. The capacitance reducing layer 22 can achieve the effect as long as it is provided, so its thickness is not particularly limited, but as an example, it can be set to 0.3 μm or more and 3 μm or less.

[0069] In addition, by providing a P between the light absorbing layer 23 and the cap layer 24 described later, - The semiconductor layer of N type can also be used as a capacitance reduction layer. - The production of semiconductor layers of type P - The semiconductor layer of the type is easy to be more electron-free than P - In view of the high mobility of carriers in the layer, it is considered that N is formed directly below the light absorbing layer 23 (between the light absorbing layer 23 and the buffer layer 21, in contact with the light absorbing layer 23). - The capacitance reducing layer 22 of the type is more effective.

[0070] In addition, in the semiconductor light-receiving element 1, the light-absorbing layer 23 is a single layer. The light-absorbing layer 23 is a single layer, which means that the light-absorbing layer 23 does not have a stacked structure composed of two or more layers with different stacked compositions or characteristics. More specifically, the light-absorbing layer 23 is a single layer, which means that, for example, it does not have a superlattice structure composed of a plurality of layers with different compositions repeatedly stacked.

[0071] The cap layer 24 has a second conductivity type (here, P type, as an example, P + The cap layer 24 includes InAsP or InGaAsP. Here, the cap layer 24 includes InAsP. As an example, the cap layer 24 is made of P + -InAs 0.15 The cap layer 24 has a thickness of, for example, 0.05 μm or more and 2.5 μm or less.

[0072] The contact layer 25 has a second conductivity type (here, P type, as an example, P+ The contact layer 25 includes InGaAs. As an example, the contact layer 25 is made of P + -InGaAs. The thickness of the contact layer 25 is, for example, not less than 0.025 μm and not more than 0.2 μm. Thus, the semiconductor stack 20 includes a first semiconductor layer of the second conductivity type, which is located on the opposite side of the substrate 10 relative to the light absorbing layer 23 and is bonded to the light absorbing layer 23. The first semiconductor layer includes a cap layer 24 and a contact layer 25.

[0073] In addition, in the above example, N + The N-type impurity concentration is 1×10 17 cm -3 N - The N-type impurity concentration is 3.0×10 16 cm -3 The degree is below, which is relatively low compared with N+ type. + The concentration of P-type impurities is 1×10 17 cm -3 above the level.

[0074] The semiconductor light receiving element 1 includes a protective film (passivation film) F. The protective film F is, for example, an insulating film. A portion of the surface 20a (top surface) of the semiconductor stack portion 20 and a side surface 20s of the semiconductor stack portion 20 extending from the periphery of the surface 20a toward the substrate 10 are covered with the protective film F. On the other hand, the remaining portion of the surface 20a of the semiconductor stack portion 20 and a portion of the surface of the contact layer 25 are exposed from the opening Fp of the protective film F.

[0075] Furthermore, the bonding portion 4a of the electrode 4 is formed in the portion of the surface 20a exposed from the protective film F, and the bonding between the electrode 4 and the semiconductor stack portion 20 (contact layer 25) is formed. That is, the electrode 4 is connected to the second portion of the second conductivity type located on the opposite side of the substrate 10 relative to the light absorbing layer 23 in the semiconductor stack portion 20 (here, the surface of the contact layer 25). On the other hand, a portion of the surface of the portion 21p of the buffer layer 21 is exposed from the opening Fn of the protective film F, and the bonding portion 5a of the electrode 5 is formed in the exposed portion, and the bonding between the electrode 5 and the semiconductor stack portion 20 (buffer layer 21) is formed. That is, the electrode 5 is connected to the first portion of the first conductivity type located on the substrate 10 side relative to the light absorbing layer 23 in the semiconductor stack portion 20 (the surface of the buffer layer 21).

[0076] Here, the semiconductor light receiving element 1 has a light receiving portion 2 including the semiconductor stacked portion 20 described above, and a waveguide portion 3 that propagates light toward the light receiving portion 2. The waveguide portion 3 includes a buffer layer 21 and a capacitance reduction layer 22 provided on the surface 10a of the substrate 10. More specifically, the buffer layer 21 and the capacitance reduction layer 22 are respectively provided to extend to the outside of the light receiving portion 2 (semiconductor stacked portion 20) along the Y-axis direction (a second direction intersecting the first direction) according to the surface 10a and the back surface 10b of the substrate 10, and the waveguide portion 3 is formed by the portions of the buffer layer 21 and the capacitance reduction layer 22 extending to the outside of the light receiving portion 2.

[0077] In other words, the buffer layer 21 includes a portion 21q included in the semiconductor stack portion 20 and a portion 21r extending from the side surface 20s of the semiconductor stack portion 20 to the outside of the semiconductor stack portion 20, and the capacitance reducing layer 22 includes a portion 22q included in the semiconductor stack portion 20 and a portion 22r extending from the side surface 20s of the semiconductor stack portion 20 to the outside of the semiconductor stack portion 20. The waveguide portion 3 is formed by the portions 21r and 22r. The surface of the portion 22r opposite to the substrate 10 is covered with a protective film F.

[0078] The semiconductor light receiving element 1 is a side-incident type that receives the light L guided by the buffer layer 21 and the capacitance reduction layer 22 in the waveguide portion 3 from the side surface 20s of the semiconductor stack portion 20. Therefore, in the semiconductor light receiving element 1, the buffer layer 21 and the capacitance reduction layer 22 are also optical waveguide layers of the first conductivity type provided between the substrate 10 and the light absorbing layer 23. The refractive indexes of the buffer layer 21, the capacitance reduction layer 22, and the light absorbing layer 23 become higher in this order.

[0079] Therefore, the light L propagating in the waveguide portion 3 is mainly distributed in the capacitance reduction layer 22, and at the same time, it is incident on the semiconductor stack portion 20 from the side 20s of the semiconductor stack portion 20, migrates from the buffer layer 21 and the capacitance reduction layer 22 side to the light absorption layer 23 and is absorbed in the light absorption layer 23. That is, the semiconductor light receiving element 1 is a side-incident type. The light L incident from the side 20s reaches the light absorption layer 23 via the optical waveguide layer. The width of the light absorption layer 23 along the incident direction (Y-axis direction) of the light L relative to the side 20s is, for example, greater than 2 μm and less than 10 μm. In addition, by making the refractive index of the light absorption layer 23 lower than the refractive index of the cap layer 24, the light L can be appropriately confined in the light absorption layer 23. In addition, the refractive index of the substrate 10 can be lower than the refractive index of the buffer layer 21, or higher than the refractive index of the buffer layer 21.

[0080] As described above, the semiconductor light receiving element 1 is adapted to receive light in a wavelength band for optical communication such as the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band. In the semiconductor light receiving element 1, the light absorbing layer 23 provided on the substrate 10 includes Inx Ga 1-x As. Moreover, the In composition x of the light absorbing layer 23 is greater than 0.55 (and less than 1). x Ga 1-x The In composition x of As is set to be 0.55 or more ( Figure 4 G2), for example, with Figure 4 Compared with the case where the In composition x is 0.53 shown in the graph G1, the absorption coefficient is improved (in Figure 4 In the example above, the improvement is twice as high in the 1.55 μm band. Figure 4 Graph G0 of FIG. 1 shows a case where a light absorbing layer composed of InGaAsP is used.

[0081] Therefore, even if the thickness of the light absorbing layer 23 is thinned to less than 1.8 μm, the sensitivity can be avoided from being reduced. That is, it is possible to increase the speed. Furthermore, the semiconductor light receiving element 1 is a side-incident type in which light is incident on the semiconductor stacking part 20 from the side 20s of the semiconductor stacking part 20, and the light incident from the side 20s reaches the light absorbing layer 23 via the optical waveguide layer (at least the capacitance reduction layer 22) on the substrate 10 side of the light absorbing layer 23. In other words, in the semiconductor light receiving element 1, the light is incident at least obliquely with respect to the Y-axis direction intersecting the thickness of the light absorbing layer 23. As a result, compared with the case where light is directly incident from the end face of the light absorbing layer along the Y-axis direction, the area of ​​light absorption in the light absorbing layer 23 is increased. As a result, there is no local increase in the light carrier density, and the degradation of characteristics such as frequency characteristics and linearity is suppressed. Therefore, according to the semiconductor light receiving element 1, it is possible to increase the speed while suppressing the degradation of characteristics. Furthermore, according to the semiconductor light receiving element 1 , the width of the light absorbing layer 23 in the incident direction of light can be set to 10 μm or less while avoiding a decrease in sensitivity, thereby reducing the capacitance of the light absorbing layer 23 and achieving further speed increase.

[0082] In addition, in the semiconductor light-receiving element 1, the semiconductor stacked portion 20 includes a first conductivity type buffer layer 21 provided between the substrate 10 and the light-absorbing layer 23. Therefore, by increasing the impurity concentration of the buffer layer 21, the buffer layer 21 can be appropriately used for forming a contact with the electrode 5. In addition, by providing the buffer layer 21 below the light-absorbing layer 23, it is possible to suppress the degradation of the response.

[0083] In the semiconductor light-receiving element 1, the buffer layer 21 includes strain relaxation layers (first to third buffer layers) having lattice constants between the lattice constants of the substrate 10 and the light-absorbing layer 23. Therefore, the crystallinity of the semiconductor stack 20 is improved, and an increase in dark current is suppressed.

[0084] In addition, in the semiconductor light-receiving element 1, the buffer layer 21 includes a plurality of strain relaxation layers (first to third buffer layers), and the plurality of strain relaxation layers are provided so that the lattice constant gradually approaches the lattice constant of the light-absorbing layer 23 as it goes from the substrate 10 toward the light-absorbing layer 23. Therefore, the crystallinity of the semiconductor stacked portion is reliably improved, and the increase of dark current is suppressed.

[0085] In addition, in the semiconductor light receiving element 1, the semiconductor stacking portion 20 includes a second conductive type cap layer 24 (first semiconductor layer) provided on the light absorbing layer 23 on the opposite side of the substrate 10 relative to the light absorbing layer 23 and including InAsP, and a second conductive type contact layer 25 (first semiconductor layer) provided on the cap layer 24 on the opposite side of the substrate 10 relative to the light absorbing layer 23 and including InGaAs. Moreover, the second portion of the connecting electrode 4 is the surface of the contact layer 25. Therefore, the contact resistance of the electrode 4 can be reduced, and the series resistance can be reduced. Thus, the deterioration of the responsiveness can be suppressed. In addition, by using a material with a refractive index lower than the refractive index of the light absorbing layer 23 as the cap layer 24, light can be appropriately confined in the light absorbing layer 23.

[0086] In addition, in the semiconductor light-receiving element 1, the semiconductor stacked portion 20 includes a first conductivity type capacitance reducing layer 22, which is disposed between the substrate 10 (buffer layer 21) and the light absorbing layer 23 and has an impurity concentration lower than that of the buffer layer 21. In this way, by providing the capacitance reducing layer 22 having a relatively low impurity concentration, the capacitance reducing layer 22 is depleted when a bias is applied, thereby achieving further speed increase by reducing the capacitance.

[0087] In addition, in the semiconductor light-receiving element 1, the capacitance reduction layer 22 is arranged between the light absorption layer 23 and the buffer layer 21, and has an impurity concentration higher than the impurity concentration of the light absorption layer 23, and has a band gap larger than the band gap of the light absorption layer 23. The capacitance reduction layer 22 is a layer with a relatively low impurity concentration as described above, which helps to reduce the capacitance. However, if only the impurity concentration of the capacitance reduction layer 22 is reduced, the potential barrier between the layers becomes larger, which may lead to degradation of the response. On the other hand, if the impurity concentration of the capacitance reduction layer 22 is increased, the depletion layer cannot be widened, and therefore, it is difficult to fully reduce the capacitance.

[0088] Therefore, as described above, when the impurity concentration of the capacitance reducing layer 22 is reduced, the absorption of light in the capacitance reducing layer 22 and the generation of carriers in the capacitance reducing layer 22 due to the absorption of light are suppressed by making the capacitance reducing layer 22 have a larger band gap than the light absorbing layer 23, thereby suppressing the degradation of the response. In addition, since the capacitance reducing layer 22 has a larger band gap than the light absorbing layer 23 and, on the other hand, has a higher impurity concentration than the light absorbing layer 23, the potential barrier in the capacitance reducing layer 22 is reduced.

[0089] In the semiconductor light-receiving element 1, the thickness of the capacitance-reducing layer 22 is 0.3 μm or more and 3.0 μm or less, and the impurity concentration of the capacitance-reducing layer 22 is 2.0×10 14 cm -3 Above and 3.0×10 16 cm -3 Therefore, by setting the upper limit of the impurity concentration of the capacitance reduction layer 22 as described above, it can be appropriately depleted when a bias voltage is applied. In addition, by setting the thickness of the capacitance reduction layer 22 to the above range, it is possible to suppress a decrease in response speed and an increase in the series resistance of the semiconductor light-receiving element 1.

[0090] In addition, in the semiconductor light receiving element 1, the In composition x in the light absorbing layer 23 is 0.57 or more, and the thickness of the light absorbing layer 23 is 1.2 μm or less. Furthermore, in the semiconductor light receiving element 1, the In composition x in the light absorbing layer 23 is 0.59 or more, and the thickness of the light absorbing layer 23 is 0.7 μm or less. Therefore, the light absorbing layer 23 is further thinned to achieve high speed.

[0091] In the semiconductor light-receiving element 1, the substrate 10 includes a semi-insulating semiconductor. Therefore, by providing the pad portion 5b of the electrode 5 on the substrate 10, the pad capacitance can be reduced, and the speed can be increased.

[0092] In the semiconductor light-receiving element 1 , the buffer layer 21 constitutes at least a part of the optical waveguide layer, but may include a layer that is semi-insulated by doping with Fe. In this case, the capacitance can be reduced.

[0093] In addition, in the semiconductor light-receiving element 1, the semiconductor stacked portion 20 may include a third semiconductor layer, which is provided between the light-absorbing layer 23 and the cap layer 24 and has a band gap between the band gap of the light-absorbing layer 23 and the band gap of the cap layer 24. In this case, by providing a layer having a band gap between the light-absorbing layer 23 and the cap layer 24, the potential barrier between the layers can be reduced, and the degradation of the response can be suppressed.

[0094] In addition, the following lists examples of combinations of each wavelength band, the thickness of the light absorbing layer 23, and the In composition x of the light absorbing layer 23. In addition, for example, the following (5) is not limited to the C-band, and can be similarly configured in the O-band and L-band.

[0095] (1) C-band.

[0096] Sensitivity: 0.86A / W or more.

[0097] Cut-off frequency: 20 GHz or more (in the case of 28 GB, etc.).

[0098] Absorption layer thickness: 1.5μm.

[0099] In composition x: x=0.55.

[0100] (2) C-band.

[0101] Sensitivity: 0.90A / W or more.

[0102] Cut-off frequency: 20 GHz or more (in the case of 28 GB high sensitivity products) Absorption layer thickness: 1.5 μm.

[0103] In composition x: x=0.57.

[0104] (3) C-band.

[0105] Sensitivity: 0.80A / W or more.

[0106] Cut-off frequency: 30 GHz or more (for 56 GB, etc.).

[0107] Absorption layer thickness: 1.2μm.

[0108] In composition x: x=0.57.

[0109] (4) C-band.

[0110] Sensitivity 0.85A / W or above.

[0111] Cut-off frequency: 30 GHz or more (for 56 GB high sensitivity products) Absorption layer thickness: 1.2 μm.

[0112] In composition x: x=0.59.

[0113] (5) C-band.

[0114] Sensitivity above 0.7A / W.

[0115] Cut-off frequency: 45 GHz or higher (for 96 GB, etc.).

[0116] Absorption layer thickness: 0.7μm.

[0117] In composition x: x=0.59.

[0118] (6) C-band.

[0119] Sensitivity 0.90A / W or above.

[0120] Cut-off frequency: 16 GHz or higher (for example, 25 GB).

[0121] Absorption layer thickness: 1.8μm.

[0122] In composition x: x=0.55.

[0123] (7) C-band.

[0124] Sensitivity 0.93A / W or above.

[0125] Cut-off frequency: 16 GHz or higher (for example, 25 GB).

[0126] Absorption layer thickness: 1.8μm.

[0127] In composition x: x=0.57.

[0128] [Second embodiment]

[0129] Figure 5 FIG. 2 is a schematic cross-sectional view of a semiconductor light-receiving element according to the second embodiment. Figure 5 As shown, the semiconductor light receiving element 1A is different from the semiconductor light receiving element 1 of the first embodiment in that it includes a semiconductor stacked portion 20A instead of the semiconductor stacked portion 20. The semiconductor stacked portion 20A includes an optical waveguide layer 27A in addition to the layers of the semiconductor stacked portion 20. The optical waveguide layer 27A is provided between the light absorbing layer 23 and the substrate 10, more specifically, between the buffer layer 21 and the substrate 10.

[0130] The optical waveguide layer 27A is in contact with the surface 10a of the substrate 10. In the semiconductor light receiving element 1A, the refractive index increases in the order of the optical waveguide layer 27A, the buffer layer 21, the capacitance reduction layer 22, and the light absorption layer 23. The optical waveguide layer 27A contains, for example, InGaAsP. In order to reduce light loss, the optical waveguide layer 27A may be composed of a material that does not contain a dopant (for example, a non-doped material). Alternatively, for the same reason, the optical waveguide layer 27A may also be composed of an insulating material. In addition, the refractive index of the substrate 10 may be lower than the refractive index of the optical waveguide layer 27A, or may be higher than the refractive index of the optical waveguide layer 27A.

[0131] The optical waveguide layer 27A includes a portion 27q included in the semiconductor stack portion 20A and a portion 27r extending from the side surface 20s of the semiconductor stack portion 20A to the outside of the semiconductor stack portion 20A. The surface of the portion 27r on the opposite side of the substrate 10 is covered with a protective film F. In the semiconductor light receiving element 1A, the waveguide portion 3 is formed by the portion 27r. The semiconductor light receiving element 1A is set to a side-incident type that receives the light L guided by the optical waveguide layer 27A (portion 27r) in the waveguide portion 3 from the side surface 20s of the semiconductor stack portion 20A. In the semiconductor light receiving element 1A, the light L propagating in the waveguide portion 3 (optical waveguide layer 27A) is incident on the semiconductor stack portion 20A from the side surface 20s of the semiconductor stack portion 20A, migrates from the optical waveguide layer 27A side to the light absorption layer 23, and is absorbed in the light absorption layer 23. That is, the semiconductor light receiving element 1A is a side-incident type. Light L incident from the side surface 20 s reaches the light absorbing layer 23 via the optical waveguide layer 27A (and the buffer layer 21 and the capacitance reducing layer 22 ).

[0132] On the other hand, in the semiconductor light receiving element 1A, the buffer layer 21 and the capacitance reduction layer 22 are terminated at the side surface 20s (the end surfaces of the buffer layer 21 and the capacitance reduction layer 22 are set flush with the end surface of the light absorbing layer 23), and do not extend outside the side surface 20s. In the semiconductor light receiving element 1A, the semiconductor stacked portion 20A includes a first conductivity type buffer layer 21 (second semiconductor layer) provided between the optical waveguide layer 27A and the light absorbing layer 23, and a first conductivity type capacitance reduction layer 22 having an impurity concentration lower than that of the buffer layer 21 and provided between the buffer layer 21 and the light absorbing layer 23. The capacitance reduction layer 22 is provided between the light absorbing layer 23 and the optical waveguide layer 27A, has an impurity concentration higher than that of the light absorbing layer 23, and has a band gap larger than that of the light absorbing layer 23.

[0133] The semiconductor light receiving element 1A described above can also achieve the same effects as the semiconductor light receiving element 1. In particular, in the semiconductor light receiving element 1A, the optical waveguide layer 27A and the buffer layer 21 that are responsible for the propagation of light to the light receiving unit 2 are configured as separate layers. Therefore, light loss (caused by free electron absorption) caused by increasing the impurity concentration of the optical waveguide layer 27A does not occur, and by increasing the impurity concentration of the buffer layer 21, the buffer layer 21 can be appropriately used for forming a contact with the electrode 5.

[0134] In the semiconductor light-receiving element 1A, the semiconductor stacked portion 20A includes a first conductivity type buffer layer 21 (second semiconductor layer) provided between the optical waveguide layer 27A and the light absorbing layer 23, and a first conductivity type capacitance reducing layer 22 having an impurity concentration lower than that of the buffer layer 21 and provided between the buffer layer 21 and the light absorbing layer 23. In this way, by providing the capacitance reducing layer 22 having a relatively low impurity concentration, the capacitance reducing layer 22 is depleted when a bias is applied, thereby achieving further speed increase by reducing the capacitance.

[0135] [Third Embodiment]

[0136] Figure 6 FIG. 1 is a schematic cross-sectional view of a semiconductor light-receiving element according to the third embodiment. Figure 6 As shown, the semiconductor light receiving element 1B is different from the semiconductor light receiving element 1 of the first embodiment in that it includes a semiconductor stacked portion 20B instead of the semiconductor stacked portion 20. The semiconductor stacked portion 20B is different from the semiconductor stacked portion 20 in that it includes an electron transport layer 22B instead of the capacitance reducing layer 22, includes a light absorbing layer 23B instead of the light absorbing layer 23, and includes a diffusion barrier layer 24B instead of the cap layer 24.

[0137] The light absorbing layer 23B contains In x Ga 1-x As has a second conductivity type (here, P type, as an example, P + Type). The In composition x of the light absorbing layer 23B is greater than 0.55 (and less than 1). As an example, the In composition x may be greater than 0.57, and herein is greater than 0.59 (as an example, 0.59). In addition, the thickness of the light absorbing layer 23B is less than 1.8 μm. As an example, the thickness of the light absorbing layer 23B may be less than 0.3 μm, and herein, may be less than 0.1 μm. As an example, the thickness of the light absorbing layer 23B may also be set to be greater than 0.02 μm and less than 0.5 μm. The width of the light absorbing layer 23B along the incident direction (Y-axis direction) of the light L relative to the side surface 20s is, for example, greater than 2 μm and less than 10 μm.

[0138] The electron transport layer 22B is provided between the light absorbing layer 23B and the buffer layer 21 and has a first conductivity type (here, N type, as an example, N - As an example, the electron transport layer 22B is made of N - -InAs 0.15The electron transport layer 22B has an impurity concentration lower than that of the buffer layer 21. The thickness of the electron transport layer 22B is, for example, 0.1 μm to 3.0 μm, or 0.3 μm to 3.0 μm. In addition, the impurity concentration of the electron transport layer 22B is 2.0×10 14 cm -3 Above and 3.0×10 16 cm -3 The following degree.

[0139] The diffusion barrier layer 24B has a second conductivity type (here, P type, as an example, P + The diffusion barrier layer 24B includes InAsP or InGaAsP. Here, the diffusion barrier layer 24B includes InAsP. As an example, the diffusion barrier layer 24B is made of P + -InAs 0.15 The thickness of the diffusion barrier layer 24B is, for example, not less than 0.05 μm and not more than 2.5 μm. Thus, the semiconductor stack portion 20B includes a fourth semiconductor layer of the second conductivity type, which is located on the opposite side of the substrate 10 relative to the light absorbing layer 23B and is bonded to the light absorbing layer 23B. The fourth semiconductor layer includes the diffusion barrier layer 24B and the contact layer 25.

[0140] In addition, in the semiconductor light receiving element 1B, the buffer layer 21 and the electron transport layer 22B are extended to the outside of the semiconductor stacked portion 20B, similar to the buffer layer 21 and the capacitance reduction layer 22 of the semiconductor light receiving element 1, to form the waveguide portion 3. That is, the semiconductor light receiving element 1B is a side-incident type. In the semiconductor light receiving element 1B, the buffer layer 21 and the electron transport layer 22B are also optical waveguide layers of the first conductivity type provided between the substrate 10 and the light absorbing layer 23B. In the semiconductor light receiving element 1B, the light L incident from the side 20s reaches the light absorbing layer 23B via the optical waveguide layer.

[0141] Even the semiconductor light receiving element 1B described above can exert the same effect as the semiconductor light receiving element 1. In addition, in the semiconductor light receiving element 1B, by setting the UTC structure, only the movement of electrons is considered, and when the light absorption layer 23B is thin, the responsiveness is expected to be improved. In addition, compared with InP, the mobility of electrons in InAsP and InGaAsP can be expected to be faster, so the responsiveness can also be expected to be improved at the same film thickness.

[0142] In addition, in the semiconductor light receiving element 1B, the semiconductor stacked portion 20B includes a second conductivity type diffusion barrier layer 24B provided on the light absorbing layer 23B on the opposite side of the substrate 10 relative to the light absorbing layer 23B and including InAsP, and a second conductivity type contact layer 25 provided on the diffusion barrier layer 24B on the opposite side of the substrate 10 relative to the light absorbing layer 23B and including InGaAs. Moreover, the fourth semiconductor layer includes the contact layer 25 and the diffusion barrier layer 24B, and the second portion of the connection electrode 4 is the surface of the contact layer 25. Therefore, the contact resistance of the electrode 4 can be reduced, and the series resistance can be reduced. Thus, the deterioration of the responsiveness can be suppressed. In addition, by using a material with a refractive index lower than the refractive index of the light absorbing layer 23B as the diffusion barrier layer 24B, light can be appropriately confined in the light absorbing layer 23B.

[0143] In the semiconductor light-receiving element 1B, the thickness of the electron transport layer 22B is 0.3 μm or more and 3.0 μm or less, and the impurity concentration of the electron transport layer 22B is 2.0×10 14 cm -3 Above and 3.0×10 16 cm -3 Therefore, by setting the upper limit of the impurity concentration of the electron transport layer 22B as described above, it can be properly depleted when a bias is applied. In addition, by setting the thickness of the electron transport layer 22B to the above range, it is possible to suppress the decrease in response speed and the increase in the series resistance of the semiconductor light-receiving element 1B.

[0144] In addition, in the semiconductor light receiving element 1B, the buffer layer 21 and the diffusion barrier layer 24B can be terminated at the side surface 20s (the end surfaces of the buffer layer 21 and the diffusion barrier layer 24B are set flush with the end surface of the light absorbing layer 23B), and the optical waveguide layer 27A can be provided between the buffer layer 21 and the substrate 10, as in the semiconductor light receiving element 1A. In this case, the semiconductor stacked portion 20B includes a first conductivity type buffer layer 21 (fifth semiconductor layer) provided between the optical waveguide layer 27A and the light absorbing layer 23B, and a first conductivity type electron transport layer 22B having an impurity concentration lower than that of the buffer layer 21 and provided between the buffer layer 21 and the light absorbing layer 23B. In this way, by relatively reducing the impurity concentration of the electron transport layer 22B, the electron transport layer 22B is depleted when a bias is applied, thereby achieving further speed increase by reducing the capacitance.

[0145] In this case, the electron transport layer 22B may be provided between the light absorbing layer 23B and the optical waveguide layer 27A, and may have an impurity concentration lower than that of the light absorbing layer 23B, and may have a band gap larger than that of the light absorbing layer 23B. In this case, the capacitance can be reduced by relatively reducing the impurity concentration of the electron transport layer 22B. In addition, by reducing the impurity concentration of the electron transport layer 22B, depletion is facilitated, and the potential barrier between the electron transport layer 22B and the light absorbing layer 23B can also be reduced.

[0146] In addition, in the semiconductor light receiving element 1B, the semiconductor stacked portion 20B may include a sixth semiconductor layer provided between the light absorbing layer 23B and the diffusion barrier layer 24B, and having a band gap between the band gap of the light absorbing layer 23B and the band gap of the diffusion barrier layer 24B. In this case, by providing a layer having a band gap between the light absorbing layer 23B and the diffusion barrier layer 24B, the potential barrier between the layers can be reduced, and the degradation of the response can be suppressed.

[0147] [Fourth Embodiment]

[0148] Figure 7 FIG. 4 is a schematic cross-sectional view of a semiconductor light-receiving element according to a fourth embodiment. Figure 7 As shown, the semiconductor light receiving element 1C is different from the semiconductor light receiving element 1 of the first embodiment in that it further includes an optical waveguide layer 27C and a cladding layer 29C. In the semiconductor light receiving element 1C, similarly to the semiconductor light receiving element 1, the buffer layer 21 includes a portion 21q included in the semiconductor stack portion 20 and a portion 21r extending from the side surface 20s of the semiconductor stack portion 20 to the outside of the semiconductor stack portion 20, but the capacitance reducing layer 22 is terminated at the side surface 20s.

[0149] Furthermore, in the semiconductor light receiving element 1C, in the waveguide portion 3, an optical waveguide layer 27C and a cladding layer 29C are sequentially stacked on the portion 21r of the buffer layer 21. The optical waveguide layer 27C has a refractive index higher than at least the refractive index of the buffer layer 21 and the refractive index of the cladding layer 29C. The optical waveguide layer 27C contains, for example, InGaAsP. In order to reduce optical loss, the optical waveguide layer 27A may be composed of a material that does not contain a dopant (for example, a non-doped material). Alternatively, for the same reason, the optical waveguide layer 27C may also be composed of an insulating material.

[0150] The cladding 29C can be made of, for example, InP, InAsP, InGaAsP, etc. The cladding 29C has a refractive index lower than that of at least the optical waveguide layer 27C. The surface of the cladding 29C on the opposite side to the optical waveguide layer 27C is covered with a protective film F. The end faces of the optical waveguide layer 27C and the cladding 29C in the optical waveguide direction (Y-axis direction) are bonded to the side surface 20s of the semiconductor stack portion 20. Thus, the optical waveguide layer 27C is optically coupled to the semiconductor stack portion 20.

[0151] Here, the thickness of the optical waveguide layer 27C is thicker than the sum of the thickness of the capacitance reduction layer 22 and the thickness of the light absorption layer 23. As a result, the optical waveguide layer 27C passes from the interface between the buffer layer 21 and the capacitance reduction layer 22 to the interface between the light absorption layer 23 and the cap layer 24 in the stacking direction (Z-axis direction) of the semiconductor stack portion 20 and reaches the cap layer 24. The refractive index of the light absorption layer 23 can be higher than the refractive indexes of the capacitance reduction layer 22 and the cap layer 24. As a result, the light L that propagates in the optical waveguide layer 27C and enters the semiconductor stack portion 20 from the side 20s migrates to the light absorption layer 23 and is absorbed in the light absorption layer 23. That is, the semiconductor light receiving element 1C is a side-incident type.

[0152] In particular, in the semiconductor light receiving element 1C, the optical waveguide layer 27C and the light absorbing layer 23 are directly coupled on the side surface 20s. Therefore, in the semiconductor light receiving element 1C, the light L propagating in the optical waveguide layer 27C is directly incident on the light absorbing layer 23 along the incident direction (Y-axis direction) relative to the side surface 20s. In addition, the optical waveguide layer 27C and the cladding layer 29C can be formed by, for example, regrowing a semiconductor layer on the buffer layer 21.

[0153] Even the semiconductor light receiving element 1C described above can achieve the same effect as the semiconductor light receiving element 1, except for the effect brought about by the light L incident from the side 20s reaching the light absorbing layer 23 via the light waveguide layer. In addition, by configuring the light waveguide layer 27C on the front side of the light absorbing layer 23, the influence of the propagation of light between the core layer and the cladding layer can be reduced. As a result, the coupling efficiency can be improved, and sensitivity can be obtained at a short distance.

[0154] In addition, in the semiconductor light receiving element 1C, the semiconductor stacked portion 20 may be changed to a semiconductor stacked portion 20B, similarly to the semiconductor light receiving element 1B. In this case, the light absorbing layer 23 is changed to a light absorbing layer 23B of the second conductivity type, and the capacitance reducing layer 22 and the cap layer 24 are respectively changed to an electron transport layer 22B and a diffusion barrier layer 24B. The relationship between the optical waveguide layer 27C and the cladding layer 29C and the respective layers is the same.

[0155] [Fifth Embodiment]

[0156] Figure 8FIG. 1 is a schematic cross-sectional view of a semiconductor light-receiving element according to the fifth embodiment. Figure 8 As shown, the semiconductor light receiving element 1D is different from the semiconductor light receiving element 1 of the first embodiment in that the side surface 20s of the semiconductor stack portion 20 is covered by a protective film F. Therefore, in the semiconductor light receiving element 1D, the end surfaces of all the layers of the semiconductor stack portion 20 are flush with each other and constitute the side surface 20s. Thus, in the semiconductor light receiving element 1D, the end surface of the light absorbing layer 23 is exposed via the protective film F, so that the light L propagating in, for example, space or an optical fiber can be coupled with the end surface of the light absorbing layer 23 at the side surface 20s. Therefore, the semiconductor light receiving element 1D is a side-incident type that receives the incidence of light L from the side surface 20s of the semiconductor stack portion 20. In particular, in the semiconductor light receiving element 1D, the light L is directly incident on the light absorbing layer 23 along the incident direction (Y-axis direction) relative to the side surface 20s.

[0157] Even the semiconductor light receiving element 1D described above can achieve the same effect as the semiconductor light receiving element 1, in addition to the effect brought about by the light L incident from the side 20s reaching the light absorbing layer 23 via the light waveguide layer. In addition, by directly incident light on the light absorbing layer 23, there is no need to make the waveguide portion 3 on the chip, and the chip size can be minimized. In addition, since there is no waveguide layer, the stacked structure (for example, generated by epitaxial growth) can be considered only by the core layer (light absorbing layer) and the cladding layer, so it can be simplified.

[0158] In addition, in the semiconductor light receiving element 1D, similarly to the semiconductor light receiving element 1B, the semiconductor stacked portion 20 may be changed to a semiconductor stacked portion 20B. In this case, the light absorbing layer 23 is changed to a light absorbing layer 23B of the second conductivity type, and the capacitance reducing layer 22 and the cap layer 24 are changed to an electron transport layer 22B and a diffusion barrier layer 24B, respectively.

[0159] [Sixth Embodiment]

[0160] Fig. 9 It is a schematic top view of the semiconductor light receiving element according to the sixth embodiment. Fig.10 It is along Fig. 9 A schematic cross-sectional view along line XX. Fig.11 It is along Fig. 9 A schematic cross-sectional view of line XI-XI. Figures 7 to 9 As shown, the semiconductor light receiving element 1K includes a semiconductor stacked portion 20K provided on the surface 10a of the substrate 10. The surface 10a (main surface) of the substrate 10 includes a first region 10a1, a second region 10a2, and a third region 10a3 arranged in sequence along the X-axis direction (first direction). The semiconductor stacked portion 20K is provided on the second region 10a2.

[0161] The semiconductor light receiving element 1K includes a first conductivity type (here, N type, as an example, N + The first semiconductor portion 41K of the second conductivity type (here, P type, as an example, P + Thus, the light absorbing layer 23K and the semiconductor stacked portion 20K described later are arranged between the first semiconductor portion 41K and the second semiconductor portion 42K, and are provided to bury the first semiconductor portion 41K and the second semiconductor portion 42K. The first semiconductor portion 41K and the second semiconductor portion 42K are composed of, for example, InP, InAsP, and InGaAsP.

[0162] The protective film F covers the surface 20a of the semiconductor stacked portion 20K. On the other hand, the protective film F is provided with an opening Fn so as to expose a portion of the surface (top surface) of the first semiconductor portion 41K, and an opening Fp so as to expose a portion of the surface (top surface) of the second semiconductor portion 42K. The electrode 4 (joining portion 4a) is electrically connected to the second semiconductor portion 42K by joining via the opening Fp, and the electrode 5 (joining portion 5a) is electrically connected to the first semiconductor portion 41K by joining via the opening Fn. In addition, a contact layer may be provided between the first semiconductor portion 41K and the second semiconductor portion 42K and the electrodes 4 and 5.

[0163] The semiconductor stacked portion 20K includes a light absorbing layer 23K, an optical waveguide layer 27K provided between the light absorbing layer 23K and the substrate 10, and a cladding layer 31K provided on the light absorbing layer 23K on the opposite side of the substrate 10. The light absorbing layer 23K is I-type or a first conductivity type (e.g., N - The light absorbing layer 23K includes InGaAs. Here, the light absorbing layer 23K is composed of N - -In x Ga 1-x As. Moreover, the In composition x of the light absorbing layer 23K is greater than 0.55 (and less than 1). As an example, the In composition x may be greater than 0.57, and here is greater than 0.59 (as an example, 0.59). In addition, the thickness of the light absorbing layer 23K is greater than 0.6 μm and less than 1.8 μm. As an example, the thickness of the light absorbing layer 23K may also be less than 1.2 μm, and here is less than 0.7 μm (as an example, 0.7 μm). The width of the light absorbing layer 23K along the incident direction (Y-axis direction) of the light L relative to the side 20s is, for example, greater than 2 μm and less than 10 μm.

[0164] The cladding layer 31K may be composed of, for example, InP, InAsP, InGaAsP, etc. The cladding layer 31K has a refractive index lower than that of the light absorbing layer 23K. Here, the surface 20a of the semiconductor stacked portion 20K is a surface on the opposite side of the light absorbing layer 23K of the cladding layer 31K. The optical waveguide layer 27K may contain, for example, InGaAsP (composed of InGaAsP). In order to reduce optical loss, the optical waveguide layer 27K may be composed of a material that does not contain a dopant (for example, a non-doped material). Alternatively, for the same reason, the optical waveguide layer 27K may also be composed of an insulating material.

[0165] Similar to the optical waveguide layer 27A, the optical waveguide layer 27K includes a portion 27q included in the semiconductor stack portion 20K and a portion 27r extending from the side surface 20s of the semiconductor stack portion 20K to the outside of the semiconductor stack portion 20K. The surface of the portion 27r on the opposite side from the substrate 10 is covered with a protective film F. In the semiconductor light receiving element 1K, the waveguide portion 3 is formed by the portion 27r. The semiconductor light receiving element 1K is a side-incident type that receives the light L guided by the optical waveguide layer 27K in the waveguide portion 3 from the side surface 20s of the semiconductor stack portion 20K.

[0166] In the semiconductor light receiving element 1K, the light L propagating in the waveguide portion 3 (optical waveguide layer 27K) enters the semiconductor stack portion 20K from the side surface 20s of the semiconductor stack portion 20K, moves from the optical waveguide layer 27K side to the light absorption layer 23K, and is absorbed in the light absorption layer 23K. That is, the light L incident from the side surface 20s reaches the light absorption layer 23K via the optical waveguide layer 27K. In addition, in the semiconductor light receiving element 1K, lattice relaxation between the substrate 10 and the light absorption layer 23K can be achieved in the optical waveguide layer 27K.

[0167] The semiconductor light receiving element 1K described above can also achieve the same effects as the semiconductor light receiving element 1 of the first embodiment. In addition, by using a material having a higher refractive index than the light waveguide layer 27K and a lower refractive index than the light absorbing layer 23K, light can be guided to the absorbing layer more efficiently.

[0168] In addition, if Fig.12 As shown, in the semiconductor light receiving element 1K, the semiconductor stacked portion 20K may be directly bonded to a separately prepared substrate while the substrate 10 is removed by etching or grinding. Fig.12In the example of the embodiment, a substrate 10M including a first layer 51M and a second layer 52M stacked on each other is prepared, and the semiconductor stack portion 20K is directly bonded to the first layer 51M. In this case, the optical waveguide layer 27K of the semiconductor stack portion 20K can be directly bonded to the waveguide 53M formed in the second layer 52M. The first layer 51M and the second layer 52M contain, for example, SiO2, and the waveguide 53M contains, for example, Si. In this way, by separately constituting the substrate 10M and the semiconductor stack portion 20K and manufacturing the semiconductor light receiving element 1K by bonding, a waveguide with a large area can be manufactured at low cost.

[0169] [Seventh Embodiment]

[0170] Fig.13 and Fig.14 It is a schematic cross-sectional view of a semiconductor light-receiving element according to the seventh embodiment. Fig.13 The sixth embodiment corresponds to Fig. 9 The cross section of the cross section of the XX line, Fig.14 The sixth embodiment corresponds to Fig. 9 The cross section of the cross section of XI-XI. Fig.13 , 14 The semiconductor light receiving element 1L shown is different from the semiconductor light receiving element 1K of the sixth embodiment in that it includes a semiconductor stacked portion 20L instead of the semiconductor stacked portion 20K and in that it includes an optical waveguide layer 32L.

[0171] The semiconductor stack portion 20L is different from the semiconductor stack portion 20K in that it has a light absorption layer 23L instead of the light absorption layer 23K, and a cladding layer 33L instead of the optical waveguide layer 27K. The cladding layer 33L can be made of the same material as the cladding layer 31K. The cladding layer 33L extends to the outside of the semiconductor stack portion 20L beyond the side surface 20s of the semiconductor stack portion 20L. That is, the cladding layer 33L includes a portion 33q included in the semiconductor stack portion 20L and a portion 33r extending from the side surface 20s of the semiconductor stack portion 20L to the outside of the semiconductor stack portion 20L. The optical waveguide layer 32L is stacked on the portion 33r of the cladding layer 33L on the outside of the semiconductor stack portion 20L. The surface of the optical waveguide layer 32L on the opposite side of the substrate 10 is covered with a protective film F.

[0172] The light absorbing layer 23L corresponds to the light absorbing layer 23K having the conductivity type set to the second conductivity type (eg, P - In the semiconductor light receiving element 1L, a first conductivity type (eg, N -The electron transport layer 43 of the light absorbing layer 23L is a light absorbing layer of the type (electron transport layer 43). The materials of the electron transport layer 43 are the same as those of the electron transport layer 22B. In this way, by setting the UTC structure, only the movement of electrons is considered, and when the light absorbing layer 23L is thin, the responsiveness is expected to be improved. In addition, compared with InP, the mobility of electrons on the InAsP and InGaAsP side can be expected to be fast, so the responsiveness can also be expected to be improved under the same film thickness.

[0173] In the semiconductor light receiving element 1L, the light L propagating in the optical waveguide layer 32L and incident on the semiconductor stacked portion 20L from the side 20s migrates to the light absorbing layer 23L and is absorbed in the light absorbing layer 23L. That is, the semiconductor light receiving element 1L is a side-incident type. In particular, in the semiconductor light receiving element 1L, the optical waveguide layer 32L and the light absorbing layer 23L are directly coupled on the side 20s. Therefore, in the semiconductor light receiving element 1L, the light L propagating in the optical waveguide layer 32L is directly incident on the light absorbing layer 23L along the incident direction (Y-axis direction) relative to the side 20s.

[0174] Even the semiconductor light receiving element 1L described above can achieve the same effect as the semiconductor light receiving element 1, except for the effect brought about by the light L incident from the side 20s reaching the light absorbing layer 23 via the light waveguide layer. In addition, by arranging the light waveguide layer 32L on the front side of the light absorbing layer 23L, the influence of the propagation of light between the core layer and the cladding layer can be reduced. Thus, the coupling efficiency can be improved, and sensitivity can be obtained at a short distance.

[0175] In addition, in the semiconductor light receiving element 1L, similarly to the semiconductor light receiving element 1K, the light absorbing layer 23L may be a light absorbing layer 23K of the first conductivity type. In this case, the electron transport layer 43 may not be provided. In addition, in the semiconductor light receiving element 1K, the conductivity type of the light absorbing layer 23K may be a second conductivity type (e.g., P - type), and an electron transport layer 43 is provided.

[0176] [Other Modifications]

[0177] The above embodiment is an explanation of one aspect of the present disclosure. Therefore, the semiconductor light receiving element of the present disclosure can arbitrarily change the semiconductor light receiving elements 1, 1A, 1B, 1C, 1D, 1K, and 1L described above.

[0178] For example, in the semiconductor light-receiving elements 1, 1A, 1B, 1C, and 1D, the buffer layer 21 is not limited to containing InAsP, but may contain InGaAsP (or may be composed of InGaAsP) for the purpose of increasing the band gap and improving the transmittance in the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band. Furthermore, each layer of the semiconductor stacked portion 20 may contain other elements such as Al.

[0179] In addition, in the semiconductor light receiving element 1, 1A, 1B, 1C, 1D, the buffer layer 21 may include a strain relaxation layer whose lattice constant changes to be continuously close to the lattice constant of the light absorbing layer 23 as it moves from the substrate 10 toward the light absorbing layer 23, 23B. In addition, in the semiconductor light receiving element 1, 1A, 1C, 1D, the cap layer 24 and the contact layer 25 sequentially stacked on the light absorbing layer 23 may be omitted, and the contact layer 25 may be directly formed on the light absorbing layer 23. Even in this case, the contact resistance of the electrode 4 is reduced.

[0180] In addition, in the case of focusing on the viewpoint of high speed, in the semiconductor light receiving element 1, 1A, 1B, 1C, 1D, the light absorption layer 23, 23B can also be applied to a waveguide type semiconductor light receiving element. In the waveguide type semiconductor light receiving element, a ridge waveguide is formed on a semi-insulating InP substrate, and a light receiving portion including the light absorption layer 23, 23B is formed in the ridge waveguide. In this way, even if it is a waveguide type, by adopting the light absorption layer 23, 23B with improved absorption rate, the length of the light receiving surface along the extension direction of the waveguide can be shortened and the capacitance can be reduced. In addition, even if the thickness is set to the same, the responsiveness is improved by increasing the transmission speed of electrons.

[0181] In addition, in the semiconductor light receiving element 1, 1A, 1B, 1C, 1D, 1K, 1L, for example, the substrate 10 may be removed by etching or grinding, and then the semiconductor stacked portion 20, 20A, 20B, 20K may be bonded to the substrate made of an insulator such as quartz or a semi-insulating semiconductor other than InP (for example, gallium arsenide, etc.). In other words, in the semiconductor light receiving element 1, the substrate 10 may include an insulator or a semi-insulating semiconductor, and may be configured separately from the semiconductor stacked portion 20, 20A, 20B, 20K, and the semiconductor stacked portion 20, 20A, 20B, 20K may be bonded to the substrate 10 (for example, directly). In this way, by configuring the substrate 10 and the semiconductor stacked portion 20, 20A, 20B, 20K separately and bonding them to manufacture the semiconductor light receiving element 1, it is possible to achieve a larger diameter and suppress costs by manufacturing optical components with inexpensive materials.

[0182] In addition, when the substrate 10 and the semiconductor stacked parts 20, 20A, 20B, 20K, 20L, which are separately constructed, are bonded, direct bonding or bonding using resin can be adopted. When resin is used to bond the substrate 10 and the semiconductor stacked parts 20, 20A, 20B, 20K, 20L, the light in the target wavelength band may be absorbed depending on the properties of the resin, but this possibility does not exist in direct bonding.

[0183] In addition, in the semiconductor light receiving elements 1, 1A, 1B, 1C, 1D, 1K, and 1L, an optical circuit including electronic devices such as a MIM structure or a transistor or a spot size converter may be formed on the substrate 10.

[0184] Industrial Applicability

[0185] Provided is a semiconductor light-receiving element capable of increasing speed.

[0186] Description of Reference Numerals

[0187] 1, 1A, 1B, 1C, 1D, 1K, 1L…semiconductor light-receiving element, 20, 20A, 20B, 20K, 20L…semiconductor stacking portion, 21…buffer layer (strain relaxation layer, second semiconductor layer, fifth semiconductor layer), 22…capacitance reduction layer, 22B…electron transport layer, 23, 23B, 23K, 23L…light absorption layer, 24…cap layer (first semiconductor layer), 24B…diffusion barrier layer (fourth semiconductor layer), 25…contact layer (first semiconductor layer, fourth semiconductor layer), 27A, 27C…optical waveguide layer, 4…electrode (second electrode), 5…electrode (first electrode).

Claims

1. A semiconductor light-receiving element, wherein: A semiconductor light receiving element for receiving incident light in at least one of the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band, and generating an electrical signal based on the incident light. The semiconductor light receiving element comprises: substrate; a semiconductor stacked portion formed on the substrate, including a back surface on the substrate side, a surface on the opposite side of the substrate, and a side surface extending from the back surface toward the surface; and A first electrode and a second electrode, which are electrically connected to the semiconductor stacked portion, The semiconductor stack portion comprises: The first conductive type light absorbing layer includes In x Ga 1-x As; The first conductive type buffer layer is disposed between the substrate and the light absorbing layer; and a first semiconductor layer of a second conductivity type different from the first conductivity type, which is located on the opposite side of the substrate with respect to the light absorbing layer and is bonded to the light absorbing layer, The first electrode is connected to a first portion of the semiconductor stacked portion that is located on the substrate side relative to the light absorbing layer. The second electrode is connected to a second portion of the second conductivity type located on the opposite side of the substrate with respect to the light absorbing layer in the semiconductor stacked portion. The In composition x in the light absorbing layer is greater than 0.55, The thickness of the light absorbing layer is less than 1.8 μm, The semiconductor light receiving element is a side-incident type that receives the incident light from the side surface. A width of the light absorbing layer along an incident direction of the light with respect to the side surface is 10 μm or less.

2. The semiconductor light receiving element according to claim 1, wherein: The buffer layer includes a strain relaxation layer having a lattice constant between a lattice constant of the substrate and a lattice constant of the light absorbing layer.

3. The semiconductor light receiving element according to claim 1, wherein The semiconductor stack portion comprises: the second conductivity type cap layer is provided on the light absorbing layer on the opposite side of the substrate relative to the light absorbing layer, and comprises InAsP or InGaAsP; and The second conductivity type contact layer is provided on the cap layer on the opposite side of the substrate relative to the light absorbing layer and includes InGaAs. The first semiconductor layer includes the contact layer and the cap layer, The second portion connected to the second electrode is a surface of the contact layer.

4. The semiconductor light receiving element according to claim 1, wherein The semiconductor stack portion comprises: The first conductive type second semiconductor layer is disposed between the substrate layer and the light absorbing layer; and The first conductivity type capacitance reducing layer has an impurity concentration lower than an impurity concentration of the second semiconductor layer, and is disposed between the second semiconductor layer and the light absorbing layer.

5. The semiconductor light receiving element according to claim 3, wherein: The semiconductor stacked portion includes a third semiconductor layer provided between the light absorbing layer and the cap layer and having a band gap between a band gap of the light absorbing layer and a band gap of the cap layer.

6. The semiconductor light receiving element according to claim 1, wherein At least one layer of the buffer layer is semi-insulating by Fe doping.

7. The semiconductor light receiving element according to claim 4, wherein: The capacitance reducing layer has an impurity concentration higher than that of the light absorbing layer and a band gap larger than that of the light absorbing layer, and is provided between the light absorbing layer and the buffer layer.

8. The semiconductor light receiving element according to claim 7, wherein: The capacitance reducing layer has a thickness of 0.3 μm or more and 3.0 μm or less, The impurity concentration of the capacitance reduction layer is 2.0×10 14 cm -3 Above and 3.0×10 16 cm -3 the following.

9. The semiconductor light receiving element according to claim 1, wherein: The In composition x in the light absorbing layer is greater than 0.57, The light absorbing layer has a thickness of 1.2 μm or less.

10. The semiconductor light receiving element according to claim 9, wherein: The In composition x in the light absorbing layer is greater than 0.59, The light absorbing layer has a thickness of 0.7 μm or less.

11. The semiconductor light receiving element according to claim 1, wherein The substrate comprises an insulator or a semi-insulating semiconductor, The semiconductor stacked portion is bonded to the substrate.

12. A semiconductor light-receiving element, wherein: A semiconductor light receiving element for receiving incident light in at least one of the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band, and generating an electrical signal based on the incident light. The semiconductor light receiving element comprises: substrate; a semiconductor stacked portion formed on the substrate, including a back surface on the substrate side, a surface on the opposite side of the substrate, and a side surface extending from the back surface toward the surface; and A first electrode and a second electrode, which are electrically connected to the semiconductor stacked portion, The semiconductor stack portion comprises: The second conductive type light absorbing layer includes In x Ga 1-x As; a buffer layer of a first conductivity type different from the second conductivity type, disposed between the substrate and the light absorbing layer; and The fourth semiconductor layer of the second conductivity type is located on the opposite side of the substrate with respect to the light absorbing layer and is bonded to the light absorbing layer. The first electrode is connected to a first portion of the semiconductor stacked portion that is located on the substrate side relative to the light absorbing layer. The second electrode is connected to a second portion of the second conductivity type located on the opposite side of the substrate with respect to the light absorbing layer in the semiconductor stacked portion. The In composition x in the light absorbing layer is greater than 0.55, The thickness of the light absorbing layer is less than 1.8 μm, The semiconductor light receiving element is a side-incident type that receives the incident light from the side surface. A width of the light absorbing layer along an incident direction of the light with respect to the side surface is 10 μm or less.

13. The semiconductor light receiving element according to claim 12, wherein: The buffer layer includes a strain relaxation layer having a lattice constant between a lattice constant of the substrate and a lattice constant of the light absorbing layer.

14. The semiconductor light receiving element according to claim 12, wherein: The semiconductor stack portion comprises: The second conductivity type diffusion barrier layer is provided on the light absorbing layer on the opposite side of the substrate relative to the light absorbing layer, and comprises InAsP or InGaAsP; as well as The second conductivity type contact layer is provided on the diffusion barrier layer on the opposite side of the substrate relative to the light absorbing layer and includes InGaAs, The fourth semiconductor layer includes the contact layer and the diffusion barrier layer, The second portion connected to the second electrode is a surface of the contact layer.

15. The semiconductor light receiving element according to claim 12, wherein: The semiconductor stack portion includes a first conductivity type electron transport layer provided between the buffer layer and the light absorbing layer, The impurity concentration of the electron transport layer is lower than the impurity concentration of the buffer layer.

16. The semiconductor light receiving element according to claim 14, wherein: The semiconductor stacked portion includes a sixth semiconductor layer provided between the light absorbing layer and the diffusion barrier layer and having a band gap between a band gap of the light absorbing layer and a band gap of the diffusion barrier layer.

17. The semiconductor light receiving element according to claim 12, wherein: At least one layer of the buffer layer is semi-insulating by Fe doping.

18. The semiconductor light receiving element according to claim 15, wherein: The electron transport layer has an impurity concentration lower than that of the light absorbing layer and a band gap larger than that of the light absorbing layer, and is disposed between the light absorbing layer and the buffer layer.

19. The semiconductor light receiving element according to claim 18, wherein: The thickness of the electron transport layer is greater than or equal to 0.3 μm and less than or equal to 3.0 μm. The impurity concentration of the electron transport layer is 2.0×10 14 cm -3 Above and 3.0×10 16 cm -3 the following.

20. The semiconductor light receiving element according to claim 12, wherein: The In composition x in the light absorbing layer is greater than 0.57, The light absorbing layer has a thickness of 0.3 μm or less.

21. The semiconductor light receiving element according to claim 12, wherein: The In composition x in the light absorbing layer is greater than 0.59, The light absorbing layer has a thickness of 0.1 μm or less.

22. The semiconductor light receiving element according to claim 12, wherein: The substrate comprises an insulator or a semi-insulating semiconductor, The semiconductor stacked portion is bonded to the substrate.

23. A semiconductor light receiving element, wherein: A semiconductor light receiving element for receiving incident light in at least one of the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band, and generating an electrical signal based on the incident light. The semiconductor light receiving element comprises: A substrate having a main surface including a first region, a second region, and a third region sequentially arranged along a first direction; a semiconductor stacked portion formed on the second region, including a back surface on the substrate side, a surface on the opposite side of the substrate, and a side surface extending from the back surface toward the surface; A first semiconductor portion of a first conductivity type formed on the first region; a second semiconductor portion of a second conductivity type different from the first conductivity type, formed on the third region; a first electrode electrically connected to the first semiconductor portion; a second electrode electrically connected to the second semiconductor portion; as well as an optical waveguide formed on the second region, extending along the main surface and along a second direction intersecting the first direction toward the side surface and coupled to the side surface, The semiconductor stack portion includes: a light absorbing layer including In x Ga 1-x As, The In composition x in the light absorbing layer is greater than 0.55, The thickness of the light absorbing layer is less than 1.8 μm, The semiconductor light receiving element is a side-incident type that receives the incident light from the side surface via the optical waveguide. A width of the light absorbing layer along an incident direction of the light with respect to the side surface is 10 μm or less.

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