Semiconductor light receiving element

Abstract

A semiconductor light-receiving element (1) is provided with: a substrate (10); a semiconductor laminated part (20) which is formed on the substrate (10), has a rear surface (10b) on the substrate (10) side, a front surface (10a) on the opposite side from the substrate (10), and a side surface (20s) extending from the rear surface (10b) to the front surface (10a), and which includes a light absorption layer (23) of a first conductivity type containing InxGa1-xAs; the optical waveguide layers (21, 22) of the first conductivity type are provided between the substrate (10) and the light absorption layer (23), and the first semiconductor layer (24) of a second conductivity type different from the first conductivity type is located on the opposite side of the light absorption layer (23) from the substrate (10) and bonded to the light absorption layer (23), and the In composition x in the light absorption layer (23) is 0.55 or more. The thickness of the light-absorbing layer (23) is 1.8 [mu] m or less, the semiconductor light-receiving element (1) is of a side surface incidence type that receives the incidence of the light from the side surface (20s), and the light incident from the side surface (20s) reaches the light-absorbing layer (23) via the optical waveguide layers (21, 22).

Description

Technical Field

[0001] The present invention 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 includes 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 adjacent to the first region of the first semiconductor layer. The optical waveguide structure includes 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 includes a light absorption layer and a second semiconductor layer, wherein the light absorption layer is disposed on the first semiconductor layer, optically coupled with the optical waveguide core layer, and the wavelength of the absorption end is greater than 1612 nm, and the second semiconductor layer is disposed on the light absorption layer and has a second conductivity type. The length of the light absorption layer in the optical waveguide direction is greater than 12 μm.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2019-197794 Summary of the invention

[0006] Problems to be solved by the invention

[0007] However, for the above-mentioned technical field, it is expected that the operation speed will be further increased. Therefore, it is considered to shorten the moving distance of the electrons by thinning the light absorbing layer. However, thinning the light absorbing layer will cause a decrease in sensitivity. In contrast, in the photodiode described in Patent Document 1, the light absorbing layer is incident from a direction intersecting the thickness direction of the light absorbing layer, thereby increasing the effective absorption layer thickness (the light absorbing layer has a length of 12 μm in the optical waveguide direction). It is also believed that the decrease in sensitivity caused by the thinning of the light absorbing layer is suppressed and the speed is increased.

[0008] However, in the optical waveguide type light receiving element described in Patent Document 1, the optical waveguide core layer is directly coupled to the light absorbing layer, and light is directly incident thereon. Therefore, when the incident light is of high intensity, the photocarrier density in the region where the light is absorbed becomes extremely high, and there is a problem that the frequency characteristics, linearity and other characteristics are degraded due to the space charge effect and the like.

[0009] An object of the present invention is to provide a semiconductor light-receiving element capable of suppressing degradation of characteristics and achieving high speed.

[0010] Technical means of solving problems

[0011] The semiconductor light-receiving element of the present invention is [1] "A semiconductor light-receiving element, which is used to receive the incidence of light of at least one wavelength band of the 1.3 μm band, the 1.55 μm band and the 1.6 μm band, and generate an electrical signal in accordance with the incident light, comprising: a substrate; a semiconductor stacked portion formed on the substrate, having 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 to the surface; and a first electrode and a second electrode electrically connected to the semiconductor stacked portion, the semiconductor stacked portion comprising: x Ga 1-x "a light absorbing layer of a first conductivity type of As; an optical waveguide layer of the first conductivity type provided between the substrate and the light absorbing layer; and a first semiconductor layer of a second conductivity type different from the first conductivity type, located on the opposite side of the substrate relative to the light absorbing layer and bonded to the light absorbing layer, the first electrode being connected to a first portion of the first conductivity type located on the substrate side relative to the light absorbing layer in the semiconductor stack, the second electrode being connected to a second portion of the second conductivity type located on the opposite side of the substrate relative to the light absorbing layer in the semiconductor stack, the In composition x in the light absorbing layer being greater than 0.55, the thickness of the light absorbing layer being less than 1.8 μm, the semiconductor light receiving element being a side-incident type that receives the incident light from the side, and the light incident from the side reaches the light absorbing layer via the optical waveguide layer."

[0012] The semiconductor light-receiving element of [1] above targets light in 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, a light-absorbing layer provided on a substrate contains In x Ga 1-x As. Furthermore, 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 0.55 or more, for example, compared with the case where the In composition x is 0.53, the absorption coefficient is improved (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 absorbing layer is reduced to about 1.8 μm or less, a decrease in sensitivity can be avoided. That is, high speed can be achieved. Furthermore, the semiconductor light receiving element of the above [1] is a side-incident type in which light is incident on the semiconductor stack portion from the side of the semiconductor stack portion, but the light incident from the side reaches the light absorbing layer via the optical waveguide layer on the substrate side of the light absorbing layer. In other words, in the semiconductor light receiving element of the above [1], the light is incident at least obliquely with respect to the length direction intersecting with the thickness of the light absorbing layer. As a result, for example, compared with the case in which light is directly incident from the end surface of the light absorbing layer in the length direction as in Patent Document 1, the area where light is absorbed by the light absorbing layer 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 of the above-mentioned [1], it is possible to suppress degradation of characteristics and realize high speed.

[0013] The semiconductor light-receiving element of the present invention may also be [2] "a semiconductor light-receiving element as described in [1] above, wherein the semiconductor stack portion includes the buffer layer of the first conductive type disposed between the substrate and the light-absorbing layer". In this case, the buffer layer can be appropriately used to form contact with the first electrode. In addition, by providing a buffer layer under the light-absorbing layer, degradation of the response can be suppressed.

[0014] The semiconductor light-receiving element of the present invention may also be [3] "a semiconductor light-receiving element as described in [2] above, wherein the buffer layer comprises a strain relief 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 portion can be improved, thereby suppressing the increase in dark current.

[0015] The semiconductor light-receiving element of the present invention may also be [4] "a semiconductor light-receiving element as described in [3] above, wherein the buffer layer includes a plurality of strain relief layers arranged in such a manner 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 [5] "a semiconductor light-receiving element as described in [3] above, wherein the buffer layer includes a plurality of strain relief layers arranged in such a manner 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". In these cases, the crystallinity of the semiconductor stack portion can be reliably improved, thereby suppressing the increase in dark current.

[0016] The semiconductor light-receiving element of the present invention may also be [6] "a semiconductor light-receiving element as described in any one of the above [1] to [5], wherein the semiconductor stack portion includes: a second conductive type covering layer provided on the light-absorbing layer on the opposite side of the substrate relative to the light-absorbing layer and containing InAsP or InGaAsP; and a second conductive type contact layer provided on the covering layer on the opposite side of the substrate relative to the light-absorbing layer and containing InGaAs, the first semiconductor layer includes the contact layer and the covering 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, thereby reducing the series resistance. Thus, the deterioration of the responsiveness can be suppressed. In addition, by using a material having a refractive index lower than that of the light-absorbing layer as the covering layer, light can be appropriately confined to the light-absorbing layer.

[0017] The semiconductor light-receiving element of the present invention may also be [7] "a semiconductor light-receiving element as described in any one of the above [1] to [6], wherein the semiconductor stack portion includes: a second semiconductor layer of the first conductivity type disposed between the optical waveguide layer and the light-absorbing layer; and a capacity reduction layer of the first conductivity type having an impurity concentration lower than that of the second semiconductor layer and disposed between the second semiconductor layer and the light-absorbing layer". In this way, by providing a capacity reduction layer having a relatively low impurity concentration, the capacity reduction layer will be depleted when a bias voltage is applied, thereby enabling further speed increase to be achieved by reducing the capacity.

[0018] The semiconductor light-receiving element of the present invention may also be [8] "a semiconductor light-receiving element as described in [6] above, wherein the semiconductor stack portion includes a third semiconductor layer disposed between the light-absorbing layer and the covering layer and having a band gap between the band gap of the light-absorbing layer and the band gap of the covering layer". In this case, by disposing a layer having a band gap between the light-absorbing layer and the covering layer, it is possible to reduce the potential barrier between the layers and suppress the degradation of the response.

[0019] The semiconductor light-receiving element of the present invention may also be [9] "a semiconductor light-receiving element as described in any one of [1] to [8] above, wherein the optical waveguide layer includes a layer that is semi-insulated by doping with Fe". In this case, the capacity can be reduced.

[0020] The semiconductor light-receiving element of the present invention may also be

[10] "a semiconductor light-receiving element as described in [7] above, wherein the capacity reduction 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, and is disposed between the light-absorbing layer and the light waveguide layer". In this case, the capacity reduction layer has a relatively low impurity concentration as described above, and is a layer that contributes to capacity reduction. However, if the impurity concentration of the capacity reduction layer is simply reduced, the potential barrier between the layers becomes larger, which may cause a deterioration in response. On the other hand, when the impurity concentration of the capacity reduction layer is increased, it is difficult to sufficiently reduce the capacity because the depletion layer does not expand. Therefore, as in this case, by making the capacity reduction layer have a larger band gap than the light-absorbing layer when reducing the impurity concentration of the capacity reduction layer, the absorption of light in the capacity reduction layer and the generation of carriers in the capacity reduction layer caused by the absorption of light are suppressed, thereby suppressing the deterioration in response. In addition, since the capacity reduction layer has a larger band gap than the light-absorbing layer and, on the other hand, has a higher impurity concentration than the light-absorbing layer, the potential barrier in the capacity reduction layer can be reduced.

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

[11] "a semiconductor light-receiving element as described in [7] or

[10] above, wherein the thickness of the capacitance reduction layer is not less than 0.3 μm and not more than 3.0 μm, and the impurity concentration of the capacitance reduction layer is not less than 2.0×10 14 cm -3 Above 3.0×10 16 cm -3 In this case, by setting the upper limit of the impurity concentration of the capacity reduction layer as described above, it is possible to appropriately deplete the layer when a bias voltage is applied. In addition, by setting the thickness of the capacity reduction layer to be within the above range, it is possible to suppress a decrease in response speed and an increase in series resistance of the semiconductor light-receiving element.

[0022] The semiconductor light receiving element of the present invention may also be

[12] "a semiconductor light receiving element as described in any one of the above [1] to

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

[13] "a semiconductor light receiving element as described in the above

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

[0023] The semiconductor light-receiving element of the present invention may also be

[14] "a semiconductor light-receiving element as described in any one of [1] to

[13] above, wherein the substrate includes a semi-insulating semiconductor". In this case, the pad capacity can be reduced by setting the pad of the first electrode on the substrate, thereby achieving high speed.

[0024] The semiconductor light-receiving element of the present invention may also be

[15] "a semiconductor light-receiving element as described in any one of the above [1] to

[14] , wherein the above-mentioned substrate includes an insulator or a semi-insulating semiconductor, and the above-mentioned semiconductor stacking part is bonded to the above-mentioned substrate". In this case, the semiconductor light-receiving element is constructed by separately constituting the substrate and the semiconductor stacking part and directly bonding them, thereby achieving a large diameter and suppressing costs by embedding optical components with inexpensive materials.

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

[16] "A semiconductor light-receiving element, which is used to receive the incident light of at least one wavelength band of the 1.3 μm band, the 1.55 μm band and the 1.6 μm band, and generate an electrical signal in accordance with the incident light, comprising: a substrate; a semiconductor stacking portion formed on the substrate, having 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 to the surface; and a first electrode and a second electrode electrically connected to the semiconductor stacking portion, the semiconductor stacking portion comprising: x Ga 1-x "a light absorbing layer of a second conductivity type of As; an optical waveguide layer of a first conductivity type different from the second conductivity type provided between the substrate and the light absorbing layer; and a fourth semiconductor layer of the second conductivity type located on the opposite side of the substrate relative to the light absorbing layer and bonded to the light absorbing layer, the first electrode being connected to a first portion of the first conductivity type located on the substrate side relative to the light absorbing layer in the semiconductor stacking portion, the second electrode being connected to a second portion of the second conductivity type located on the opposite side of the substrate relative to the light absorbing layer in the semiconductor stacking portion, the In composition x in the light absorbing layer being greater than 0.55, the thickness of the light absorbing layer being less than 1.8 μm, the semiconductor light receiving element being a side-incident type receiving the incident light from the side, and the light incident from the side reaching the light absorbing layer via the optical waveguide layer."

[0026] The semiconductor light-receiving element of

[16] is targeted at light in 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 contains In x Ga 1-x As. Furthermore, 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 greater than 0.55, for example, compared with the case where the In composition x is 0.53, the absorption coefficient is improved (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 absorbing layer is reduced to about 1.8 μm or less, a decrease in sensitivity can be avoided. That is, high speed can be achieved. Furthermore, the semiconductor light receiving element of the above-mentioned

[16] is a side-incident type in which light is incident on the semiconductor stack portion from the side of the semiconductor stack portion, but the light incident from the side reaches the light absorbing layer via the optical waveguide layer on the substrate side of the light absorbing layer. In other words, in the semiconductor light receiving element of the above-mentioned

[16] , the light is incident at least obliquely with respect to the length direction intersecting with the thickness of the light absorbing layer. As a result, for example, compared with the case where light is directly incident from the end surface of the light absorbing layer in the length direction as in Patent Document 1, the area where light is absorbed by the light absorbing layer 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 of the above-mentioned

[16] , it is possible to suppress the degradation of characteristics and achieve high speed.

[0027] The semiconductor light-receiving element of the present invention may also be

[17] "a semiconductor light-receiving element as described in

[16] above, wherein the semiconductor stack portion includes a buffer layer of the first conductive type disposed between the substrate and the light-absorbing layer". In this case, the buffer layer can be appropriately used to form contact with the first electrode. In addition, by providing a buffer layer under the light-absorbing layer, degradation of the response can be suppressed.

[0028] The semiconductor light-receiving element of the present invention may also be

[18] "a semiconductor light-receiving element as described in

[17] above, wherein the buffer layer comprises a strain relief 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 portion can be improved, thereby suppressing the increase in dark current.

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

[19] "a semiconductor light-receiving element as described in

[18] above, wherein the buffer layer includes a plurality of strain relief layers arranged in such a manner 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

[20] "a semiconductor light-receiving element as described in

[18] above, wherein the buffer layer includes a plurality of strain relief layers arranged in such a manner 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". In these cases, the crystallinity of the semiconductor stack portion can be reliably improved, thereby suppressing the increase in dark current.

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

[21] "a semiconductor light-receiving element as described in any one of the above

[16] to

[20] , wherein the semiconductor stack portion includes: a diffusion barrier layer of the second conductivity type provided on the light-absorbing layer on the opposite side of the substrate relative to the light-absorbing layer and containing InAsP or InGaAsP; and a contact layer of the second conductivity type provided on the diffusion barrier layer on the opposite side of the substrate relative to the light-absorbing layer and containing 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, thereby reducing the series resistance. Thus, the deterioration of the responsiveness can be suppressed. In addition, by using a material having a refractive index lower than that of the light-absorbing layer as the diffusion barrier layer, light can be appropriately confined to the light-absorbing layer.

[0031] The semiconductor light-receiving element of the present invention may also be

[22] "a semiconductor light-receiving element as described in any one of the above

[16] to

[21] , wherein the semiconductor stack portion includes: a fifth semiconductor layer of the first conductivity type disposed between the optical waveguide layer and the light absorption layer; and an electron transport layer of the first conductivity type disposed between the fifth semiconductor layer and the light absorption layer and having an impurity concentration lower than that of the fifth semiconductor layer". In this way, by making the impurity concentration of the electron transport layer relatively low, the electron transport layer will be depleted when a bias voltage is applied, thereby enabling further speed increase to be achieved by reducing the capacity.

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

[23] "a semiconductor light-receiving element as described in

[21] above, wherein the semiconductor stack portion includes a sixth semiconductor layer disposed between the light-absorbing layer and the diffusion barrier layer and having 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 disposing a layer having a band gap between the light-absorbing layer and the diffusion barrier layer, it is possible to reduce the potential barrier between the layers and suppress the degradation of the response.

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

[24] "a semiconductor light-receiving element as described in any one of

[16] to

[23] above, wherein the optical waveguide layer includes a layer that is semi-insulated by doping with Fe". In this case, the capacity can be reduced.

[0034] The semiconductor light-receiving element of the present invention may also be

[25] "a semiconductor light-receiving element as described in

[22] above, wherein the electron transport 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, and is arranged between the light-absorbing layer and the optical waveguide layer". In this case, the capacity can be reduced by making the impurity concentration of the electron transport layer relatively low. In addition, the potential barrier between the electron transport layer and the light-absorbing layer can be reduced on the basis of making it easy to deplete by making the impurity concentration of the electron transport layer low.

[0035] The semiconductor light-receiving element of the present invention may also be

[26] "a semiconductor light-receiving element as described in

[22] or

[25] above, wherein the thickness of the electron transport layer is not less than 0.3 μm and not more than 3.0 μm, and the impurity concentration of the electron transport layer is not less than 2.0×10 14 cm -3 Above 3.0×10 16 cm -3 In this case, by making the upper limit of the impurity concentration of the electron transport layer as described above, it is possible to properly deplete it when a bias voltage is applied. In addition, by making the thickness of the electron transport layer within the above range, it is possible to suppress a decrease in response speed and an increase in series resistance of the semiconductor light-receiving element.

[0036] The semiconductor light receiving element of the present invention may also be

[27] "a semiconductor light receiving element as described in any one of the above

[16] to

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

[28] "a semiconductor light receiving element as described in any one of the above

[16] to

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

[0037] The semiconductor light-receiving element of the present invention may also be

[29] "a semiconductor light-receiving element as described in any one of

[16] to

[28] above, wherein the substrate includes a semi-insulating semiconductor". In this case, the pad capacity can be reduced by setting the pad of the first electrode on the substrate, thereby achieving high speed.

[0038] The semiconductor light-receiving element of the present invention may also be

[30] "a semiconductor light-receiving element as described in any one of

[16] to

[29] above, wherein the substrate comprises an insulator or a semi-insulating semiconductor, and the semiconductor stack portion is bonded to the substrate". In this case, the semiconductor light-receiving element is constructed by separately constituting the substrate and the semiconductor stack portion and directly bonding them together, thereby achieving a larger aperture and suppressing costs by embedding optical components with inexpensive materials.

[0039] The semiconductor light-receiving element of the present invention may also be

[31] "A semiconductor light-receiving element, which is used to receive the incident light of at least one wavelength band of the 1.3 μm band, the 1.55 μm band and the 1.6 μm band, and generate an electrical signal in response to the incident light, comprising: 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 stacking portion, which is formed on the second region and has 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 to 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; and a second electrode electrically connected to the second semiconductor portion, wherein the semiconductor stacking portion comprises: a first electrode containing In x Ga 1-xAs light absorbing layer; and an optical waveguide layer provided between the substrate and the light absorbing layer, wherein 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, and the semiconductor light receiving element is a side-incident type that receives the incident light from the side, and the light incident from the side reaches the light absorbing layer via the optical waveguide layer.

[0040] The semiconductor light-receiving element of

[31] is targeted at light in 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 contains In x Ga 1-x As. Furthermore, 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 greater than 0.55, for example, compared with the case where the In composition x is 0.53, the absorption coefficient is improved (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 absorbing layer is reduced to about 1.8 μm or less, the sensitivity can be avoided from decreasing. That is, high speed can be achieved. Furthermore, the semiconductor light receiving element of the above-mentioned

[31] is a side-incident type in which light is incident on the semiconductor stack portion from the side of the semiconductor stack portion, but the light incident from the side reaches the light absorbing layer via the optical waveguide layer on the substrate side of the light absorbing layer. In other words, in the semiconductor light receiving element of the above-mentioned

[31] , the light is incident at least obliquely with respect to the length direction intersecting with the thickness of the light absorbing layer. As a result, for example, compared with the case in which light is directly incident from the end surface of the light absorbing layer in the length direction as in Patent Document 1, the area where light is absorbed by the light absorbing layer 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

[31] mentioned above, it is possible to suppress the degradation of characteristics and achieve high speed.

[0041] Effects of the Invention

[0042] According to the present invention, it is possible to provide a semiconductor light-receiving element capable of suppressing degradation of characteristics and achieving high speed. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 It is a schematic plan view showing the semiconductor light-receiving element according to the first embodiment.

[0044] Figure 2 It is along Figure 1 Schematic cross-sectional view of line II-II.

[0045] Figure 3 It is along Figure 1 Schematic cross-sectional view along line III-III.

[0046] Figure 4 It is a graph explaining the relationship between the composition of the light absorbing layer and the absorption coefficient.

[0047] Figure 5 It is a schematic cross-sectional view of a semiconductor light-receiving element according to the second embodiment.

[0048] Figure 6 It is a schematic cross-sectional view of a semiconductor light-receiving element according to a third embodiment.

[0049] Figure 7 It is a schematic top view of a semiconductor light-receiving element according to a fourth embodiment.

[0050] Figure 8 It is along Figure 7 Schematic cross-sectional view along line VIII-VIII.

[0051] Fig. 9 It is along Figure 7 Schematic cross-sectional view along line IX-IX.

[0052] Fig.10 Yes means Fig. 9 A cross-sectional view of a modified example of the semiconductor light-receiving element shown.

[0053] Fig.11 Yes means Fig. 9 A cross-sectional view of a modified example of the semiconductor light-receiving element shown. DETAILED DESCRIPTION

[0054] Hereinafter, one embodiment will be described in detail with reference to the accompanying drawings. In addition, in each figure, the same or corresponding elements are sometimes marked with the same reference numerals, and repeated descriptions are 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 Schematic cross-sectional view of 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 communication, 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 wavelength band of the above-mentioned multiple wavelength bands, and generate an electrical signal corresponding to the incident light. The 1.3μm band is, for example, a wavelength range of 1.26μm to 1.36μm. The 1.55μm band is, for example, a wavelength range of 1.53μm to 1.565μm. The 1.6μm band is, for example, a wavelength range greater than 1.565μm and less than 1.625μm. 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 wavelength bands (that is, wavelengths other than the peak can be outside the wavelength range of the above-mentioned wavelength bands).

[0057] The semiconductor light receiving element 1 includes a substrate 10, a semiconductor stacking portion 20, an electrode 4 (a second electrode), and a pair of electrodes 5 (a first electrode). The electrode 4 includes a joint portion 4a joined to the semiconductor stacking 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 stacking 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 has a surface (main surface) 10a and a back surface 10b on the opposite side of the surface 10a. In addition, the substrate 10 has a region RA, a region RB, and a region RC arranged in sequence along the X-axis direction (first direction) along 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 is set as a semiconductor table protruding from the surface 10a. The semiconductor stack portion 20 has 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 to the surface 20a. The side 20s connects the back side 20b to the surface 20a. The semiconductor stack portion 20 has a buffer layer 21, a capacity reduction layer 22, a light absorption layer 23, a cover 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 of the contact layer 25 on the opposite side to the light absorption layer 23, and the back side 20b is the surface of the buffer layer 21 on the opposite side to the light absorption layer 23, and is in contact with 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 over the region RA and the region RC with the region RB as the center. Here, the semiconductor stack 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 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 20 as seen 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, and the third buffer layer is composed of N + -InAs 0.10 The capacity reduction 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 capacity 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 in such a manner 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 capacity reduction layer 22 is disposed on the light absorbing layer 23 side relative to 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 contains InGaAs. Here, the light absorbing layer 23 is made of N - -In x Ga 1-x As is formed. In addition, 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 here is 0.59 or more (as an example, 0.59).

[0064] In addition, the thickness of the light absorption layer 23 (the thickness along the stacking direction (Z-axis direction) of the semiconductor stacking part 20) is not less than 0.6 μm and not more than 1.8 μm. As an example, the thickness of the light absorption layer 23 can be not more than 1.2 μm, and here it is not more than 0.7 μm (as an example, it is 0.7 μm). In addition, the light absorption layer 23 can also be set as an absorption layer of a mixed crystal of Al, P, Sb, N, other materials and InGaAs in the range of a band gap of not more than 0.72 eV. The ratio of Al, P, Sb and N (or other materials) mixed in InGaAs can be, for example, not more than 5% or not more than 10%.

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

[0066] Thus, the semiconductor stacked portion 20 has a capacity reduction layer 22 provided between the buffer layer 21 and the light absorbing layer 23. As matters to be determined for the capacity reduction layer 22, as described above, the impurity concentration is higher than that of the light absorbing layer 23 and depletion occurs when a bias is applied. The reason for this is that, as described above, since the capacity reduction layer 22 has a larger band gap than the light absorbing layer 23, when the impurity concentration is low, there is a problem that a potential barrier is generated in the conduction band, and the movement of carriers with a large potential barrier is hindered, and carriers cannot be properly captured.

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

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

[0069] In addition, by providing P between the light absorbing layer 23 and the cover layer 24 described below - The semiconductor layer of N type can also be used as a capacity reduction layer. - The semiconductor layer of type P - The semiconductor layer of this type is easy to make and - The carrier speed in the layer is greater than that of electrons, and it is considered that N is formed just below the light absorbing layer 23 (between the light absorbing layer 23 and the buffer layer 21 and in contact with the light absorbing layer 23). - The capacity reduction layer 22 of this 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 means that the light-absorbing layer 23 does not have a stacked structure composed of two or more layers having different compositions or characteristics. More specifically, the light-absorbing layer 23 is a single layer, for example, does not have a superlattice structure composed of multiple layers having 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 contains InAsP or InGaAsP. Here, the cap layer 24 contains InAsP. As an example, the cap layer 24 is made of P + -InAs 0.15 The coating 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 contains InGaAs. As an example, the contact layer 25 is made of P + -InGaAs. The thickness of the contact layer 25 is, for example, 0.025 μm or more and 0.2 μm or less. Thus, the semiconductor stack 20 includes a first semiconductor layer of the second conductivity type located on the opposite side of the substrate 10 relative to the light absorbing layer 23 and 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 About 1000 N - The impurity concentration of N-type is 3.0×10 16 cm -3 Below the left and right, with N + In addition, P + The concentration of P-type impurities is 1×10 17 cm -3 Above left and right.

[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 by the protective film F. On the other hand, the remaining portion of the surface 20a of the semiconductor stack portion 20, here a portion of the surface of the contact layer 25, is exposed from the opening Fp of the protective film F.

[0075] Furthermore, a joint portion 4a of the electrode 4 is formed in the portion of the surface 20a exposed from the protective film F, and a joint is formed between the electrode 4 and the semiconductor stack portion 20 (contact layer 25). 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 a joint portion 5a of the electrode 5 is formed in the exposed portion, and a joint is formed between the electrode 5 and the semiconductor stack portion 20 (buffer layer 21). 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 for propagating light to 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 extended to the outside of the light receiving portion 2 (semiconductor stacked portion 20) along the Y-axis direction (the second direction intersecting the first direction) along 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 reduction 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 portions 21r and 22r form the waveguide portion 3. 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 buffer layer 21, the capacitance reduction layer 22, and the light absorbing layer 23 have a higher refractive index in this order.

[0079] Therefore, the light L propagating in the waveguide portion 3 is mainly distributed in the capacitance reduction layer 22 and is incident on the semiconductor stack portion 20 from the side 20s of the semiconductor stack portion 20, and 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, not less than 2 μm and not more than 10 μm. In addition, by making the refractive index of the light absorption layer 23 lower than the refractive index of the cover 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, but can also be 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 wavelength bands 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 contains In xGa 1-x As. Furthermore, 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 0.55 or more ( Figure 4 When the curve G2) is Figure 4 Compared with the case where the In composition x is 0.53 represented by the curve G1, the absorption coefficient is improved (in Figure 4 In the example above, the wavelength is increased by about 2 times in the 1.55 μm band. Figure 4 The curve G0 of FIG. 1 represents the case where a light absorption layer composed of InGaAsP is used.

[0081] Therefore, even if the thickness of the light absorbing layer 23 is reduced to about 1.8 μm or less, the sensitivity can be avoided from decreasing. That is, high speed can be achieved. 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, but the light incident from the side 20s reaches the light absorbing layer 23 via the optical waveguide layer (at least the capacity 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 with 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 ​​the light absorbing layer 23 that absorbs light 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 suppress the degradation of characteristics and achieve high speed. Furthermore, according to the semiconductor light receiving element 1, a decrease in sensitivity can be avoided, and the width of the light absorbing layer 23 in the incident direction of light can be made 10 μm or less, thereby reducing the capacity of the light absorbing layer 23 and achieving further speed increase.

[0082] Furthermore, in the semiconductor light-receiving element 1, the semiconductor stacked portion 20 includes a buffer layer 21 of the first conductivity type 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 utilized in forming the contact with the electrode 5. Furthermore, 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 can be improved, and an increase in dark current can be 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) provided in such a manner that the lattice constant gradually approaches the lattice constant of the light-absorbing layer 23 as it moves from the substrate 10 toward the light-absorbing layer 23. Therefore, the crystallinity of the semiconductor stack portion can be reliably improved, and an increase in dark current can be suppressed.

[0085] In addition, in the semiconductor light receiving element 1, the semiconductor stacking part 20 includes a second conductive type covering 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 containing InAsP, and a second conductive type contact layer 25 (first semiconductor layer) provided on the covering layer 24 on the opposite side of the substrate 10 relative to the light absorbing layer 23 and containing InGaAs. Furthermore, the second portion to which the electrode 4 is connected 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 having a refractive index lower than that of the light absorbing layer 23 as the covering layer 24, light can be appropriately confined to the absorption layer 23.

[0086] Furthermore, in the semiconductor light-receiving element 1, the semiconductor stacked portion 20 includes a first conductivity type capacity reduction layer 22 disposed between the substrate 10 (buffer layer 21) and the light-absorbing layer 23 and having an impurity concentration lower than that of the buffer layer 21. By providing the capacity reduction layer 22 having a relatively low impurity concentration, the capacity reduction layer 22 is depleted when a bias is applied, and thus further speed increase can be achieved by reducing the capacity.

[0087] In addition, in the semiconductor light-receiving element 1, the capacity reduction layer 22 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, and is disposed between the light-absorbing layer 23 and the buffer layer 21. As described above, the capacity reduction layer 22 is a layer having a relatively low impurity concentration and contributing to capacity reduction. However, simply reducing the impurity concentration of the capacity reduction layer 22 will increase the potential barrier between the layers, causing a problem of deterioration in response. On the other hand, if the impurity concentration of the capacity reduction layer 22 is increased, the depletion layer does not expand, and it is therefore difficult to sufficiently reduce the capacity.

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

[0089] In the semiconductor light-receiving element 1, the thickness of the capacitance reduction layer 22 is 0.3 μm or more and 3.0 μm or less, and the impurity concentration of the capacitance reduction layer 22 is 2.0×10 14 cm -3 Above 3.0×10 16 cm -3 Therefore, by setting the upper limit of the impurity concentration of the capacity reduction layer 22 as described above, it is possible to appropriately deplete when a bias voltage is applied. In addition, by setting the thickness of the capacity reduction layer 22 to be within 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. 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, it is possible to achieve a higher speed by further reducing the thickness of the light absorbing layer 23.

[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 capacity 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 capacity can be reduced.

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

[0094] In addition, 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 are described below. 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).

[0103] Absorption layer thickness: 1.5μm.

[0104] In composition x: x=0.57.

[0105] (3) C-band.

[0106] Sensitivity: 0.80A / W or more.

[0107] Cut-off frequency: 30 GHz or more (for 56 GB, etc.).

[0108] Absorption layer thickness: 1.2μm.

[0109] In composition x: x=0.57.

[0110] (4) C-band.

[0111] Sensitivity 0.85A / W or above.

[0112] Cut-off frequency: 30 GHz or more (in the case of 56 GB high sensitivity products).

[0113] Absorption layer thickness: 1.2μm.

[0114] In composition x: x=0.59.

[0115] (5) C-band.

[0116] Sensitivity 0.7A / W or above.

[0117] Cut-off frequency: 45 GHz or higher (for 96 GB, etc.).

[0118] Absorption layer thickness: 0.7μm.

[0119] In composition x: x=0.59.

[0120] (6) C-band.

[0121] Sensitivity 0.90A / W or above.

[0122] Cut-off frequency: 16 GHz or more (for example, 25 GB).

[0123] Absorption layer thickness: 1.8μm.

[0124] In composition x: x=0.55.

[0125] (7) C-band.

[0126] Sensitivity 0.93A / W or above.

[0127] Cut-off frequency: 16 GHz or more (for example, 25 GB).

[0128] Absorption layer thickness: 1.8μm.

[0129] In composition x: x=0.57.

[0130] [Second embodiment]

[0131] Figure 5 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 a semiconductor stacked portion 20A is provided instead of the semiconductor stacked portion 20. The semiconductor stacked portion 20A has 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.

[0132] 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 capacity reduction layer 22, and the light absorption layer 23. The optical waveguide layer 27A contains, for example, InGaAsP. The optical waveguide layer 27A can be composed of a material containing no dopant (for example, an undoped material) in order to reduce light loss. Alternatively, the optical waveguide layer 27A can also be composed of an insulating material for the same reason. In addition, the refractive index of the substrate 10 may be lower than the refractive index of the optical waveguide layer 27A, but may also be higher than the refractive index of the optical waveguide layer 27A.

[0133] 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 to 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 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, moves 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 reduction layer 22 ).

[0134] On the other hand, in the semiconductor light receiving element 1A, the buffer layer 21 and the capacity reduction layer 22 are terminated at the side surface 20s (the end surfaces of the buffer layer 21 and the capacity reduction layer 22 are flush with the end surface of the light absorbing layer 23), and do not extend to the outside of the side surface 20s. In the semiconductor light receiving element 1A, the semiconductor stacked portion 20A includes a buffer layer 21 (a second semiconductor layer) of the first conductivity type provided between the optical waveguide layer 27A and the light absorbing layer 23, and a capacity reduction layer 22 of the first conductivity type 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 capacity reduction layer 22 has an impurity concentration higher than that of the light absorbing layer 23, has a band gap larger than that of the light absorbing layer 23, and is provided between the light absorbing layer 23 and the optical waveguide layer 27A.

[0135] In the semiconductor light receiving element 1A described above, the same effects as those of the semiconductor light receiving element 1 can be obtained. In particular, in the semiconductor light receiving element 1A, the optical waveguide layer 27A and the buffer layer 21 responsible for the propagation of light to the light receiving unit 2 are configured as different layers. Therefore, the optical loss (caused by free electron absorption) caused by increasing the impurity concentration of the optical waveguide layer 27A can be avoided, and the buffer layer 21 can be appropriately used for the formation of contact with the electrode 5 by increasing the impurity concentration of the buffer layer 21.

[0136] Furthermore, in the semiconductor light-receiving element 1A, the semiconductor stacked portion 20A includes a buffer layer 21 (second semiconductor layer) of the first conductivity type provided between the optical waveguide layer 27A and the light absorbing layer 23, and a capacity reduction layer 22 of the first conductivity type provided between the buffer layer 21 and the light absorbing layer 23, which has an impurity concentration lower than that of the buffer layer 21. By providing the capacity reduction layer 22 having a relatively low impurity concentration, the capacity reduction layer 22 is depleted when a bias is applied, so that further speed-up can be achieved by reducing the capacity.

[0137] [Third Embodiment]

[0138] Figure 6 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 a semiconductor stacked portion 20B is provided instead of the semiconductor stacked portion 20. The semiconductor stacked portion 20B is different from the semiconductor stacked portion 20 in that an electron transport layer 22B is provided instead of the capacity reduction layer 22, a light absorption layer 23B is provided instead of the light absorption layer 23, and a diffusion barrier layer 24B is provided instead of the cover layer 24.

[0139] The light absorbing layer 23B contains In x Ga 1-x As, having 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 here 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 here, may also be less than 0.1 μm. As an example, the thickness of the light absorbing layer 23B may also 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 20s is, for example, greater than 2 μm and less than 10 μm.

[0140] 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 - The electron transport layer 22B is composed 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 3.0×10 16 cm -3 Below left and right.

[0141] The diffusion barrier layer 24B has a second conductivity type (here, P type, as an example, P + The diffusion barrier layer 24B contains InAsP or InGaAsP. Here, the diffusion barrier layer 24B contains 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, 0.05 μm or more and 2.5 μm or less. Thus, the semiconductor stacked portion 20B includes a fourth semiconductor layer of the second conductivity type located on the opposite side of the substrate 10 relative to the light absorbing layer 23B and bonded to the light absorbing layer 23B. The fourth semiconductor layer includes the diffusion barrier layer 24B and the contact layer 25.

[0142] In addition, in the semiconductor light receiving element 1B, the buffer layer 21 and the electron transport layer 22B extend to the outside of the semiconductor stacking part 20B like the buffer layer 21 and the capacity reduction layer 22 of the semiconductor light receiving element 1 to form the waveguide part 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 conductive 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.

[0143] In the semiconductor light receiving element 1B described above, the same effect as that of the semiconductor light receiving element 1 can be obtained. In addition, in the semiconductor light receiving element 1B, by adopting the UTC structure, considering only the movement of electrons, it is expected that the responsiveness will be improved when the light absorbing layer 23B is thin. In addition, compared with InP, since the electron mobility of InAsP and InGaAsP can be expected to be faster, it is also expected that the responsiveness will be improved at the same film thickness.

[0144] In addition, in the semiconductor light receiving element 1B, the semiconductor stacking part 20B includes a diffusion barrier layer 24B of the second conductivity type provided on the light absorbing layer 23B on the opposite side of the substrate 10 relative to the light absorbing layer 23B and containing InAsP, and a contact layer 25 of the second conductivity type provided on the diffusion barrier layer 24B on the opposite side of the substrate 10 relative to the light absorbing layer 23B and containing InGaAs. Furthermore, the fourth semiconductor layer includes the contact layer 25 and the diffusion barrier layer 24B, and the second part connected to the 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 having 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 to the light absorbing layer 23B.

[0145] 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 3.0×10 16 cm -3 Therefore, by making the upper limit of the impurity concentration of the electron transport layer 22B as described above, it is possible to appropriately deplete when a bias is applied. In addition, by making the thickness of the electron transport layer 22B within 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.

[0146] In addition, in the semiconductor light receiving element 1B, similarly to the semiconductor light receiving element 1A, the buffer layer 21 and the diffusion barrier layer 24B may terminate at the side surface 20s (the end surfaces of the buffer layer 21 and the diffusion barrier layer 24B are flush with the end surface of the light absorbing layer 23B), and the optical waveguide layer 27A may be provided between the buffer layer 21 and the substrate 10. In this case, the semiconductor stacked portion 20B includes the first conductive type buffer layer 21 (fifth semiconductor layer) provided between the optical waveguide layer 27A and the light absorbing layer 23B, and the first conductive 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. By making the impurity concentration of the electron transport layer 22B relatively low in this way, the electron transport layer 22B is depleted when a bias is applied, and thus further speed increase can be achieved by reducing the capacity.

[0147] In this case, the electron transport layer 22B may have an impurity concentration lower than that of the light absorbing layer 23B, and a band gap larger than that of the light absorbing layer 23B, and may be provided between the light absorbing layer 23B and the optical waveguide layer 27A. In this case, by making the impurity concentration of the electron transport layer 22B relatively low, it is possible to reduce the capacity. In addition, it is possible to reduce the barrier between the electron transport layer 22B and the light absorbing layer 23B on the basis of making it easier to deplete by reducing the impurity concentration of the electron transport layer 22B.

[0148] 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, thereby suppressing the degradation of the response.

[0149] [Fourth embodiment]

[0150] Figure 7 It is a schematic top view of a semiconductor light-receiving element according to a fourth embodiment. Figure 8 It is along Figure 7 Schematic cross-sectional view along line VIII-VIII. Fig. 9 It is along Figure 7 A schematic cross-sectional view of the line IX-IX. 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 has 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.

[0151] 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 below are arranged between the first semiconductor portion 41K and the second semiconductor portion 42K, and are provided in a manner embedded in 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, InGaAsP, or the like.

[0152] 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 joined to the second semiconductor portion 42K via the opening Fp and is electrically connected, and the electrode 5 (joining portion 5a) is joined to the first semiconductor portion 41K via the opening Fn and is electrically connected. 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.

[0153] 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 of I type or first conductivity type (e.g. N - The light absorbing layer 23K contains InGaAs. Here, the light absorbing layer 23K is composed of N - -In x Ga 1-x As is formed. Furthermore, 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 can be greater than 0.57, and here is greater than 0.59 (as an example, it is 0.59). In addition, the thickness of the light absorbing layer 23K is greater than 0.6μm and less than 1.8μm. As an example, the thickness of the light absorbing layer 23K can be less than 1.2μm, and here is less than 0.7μm (as an example, it is 0.7μm). 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 2μm and less than 10μm.

[0154] The cladding layer 31K can be made 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 the surface of the cladding layer 31K on the opposite side to the light absorbing layer 23K. The optical waveguide layer 27K contains, for example, InGaAsP (is made of InGaAsP). The optical waveguide layer 27K can be made of a material containing no dopant (for example, an undoped material) in order to reduce optical loss. Alternatively, the optical waveguide layer 27K can also be made of an insulating material for the same reason.

[0155] The optical waveguide layer 27K is similar to the optical waveguide layer 27A, and 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 to 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.

[0156] In the semiconductor light receiving element 1K, the light L propagating in the waveguide portion 3 (optical waveguide layer 27K) enters the semiconductor stacked portion 20K from the side surface 20s of the semiconductor stacked portion 20K, moves from the optical waveguide layer 27K side to the light absorbing layer 23K, and is absorbed in the light absorbing layer 23K. That is, the light L incident from the side surface 20s reaches the light absorbing 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 absorbing layer 23K can be achieved in the optical waveguide layer 27K.

[0157] 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. Furthermore, 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.

[0158] In addition, if Fig.10 As shown, in the semiconductor light receiving element 1K, the substrate 10 may be removed by etching, grinding, etc., and the semiconductor stacked portion 20K may be directly bonded to a separately prepared substrate. Fig.10 In the example of , 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 SiO2, for example, and the waveguide 53M contains Si, for example. By manufacturing the semiconductor light receiving element 1K by separately constituting the substrate 10M and the semiconductor stack portion 20K and bonding them together, a waveguide with a large area can be manufactured at low cost.

[0159] In addition, if Fig.11 As shown, the semiconductor light receiving element 1K can be changed to a semiconductor light receiving element 1L. The semiconductor light receiving element 1L includes a semiconductor stacking portion 20L instead of the semiconductor stacking portion 20K of the semiconductor light receiving element 1K. The semiconductor stacking portion 20L includes a semiconductor layer 20L corresponding to the conductivity type of the light absorbing layer 23K being changed to the second conductivity type (e.g., P -In addition, a first conductive type (e.g., N) light absorbing layer 22L is provided between the first conductive type first semiconductor portion 41K and the side surface 20s of the semiconductor stack portion 20L. - The electron transport layer 43 of the UTC structure is the same as that of the electron transport layer 22B. In this way, by adopting the UTC structure, considering only the movement of electrons, it is foreseeable that the responsiveness will be improved when the light absorption layer 23K is thin. In addition, compared with InP, since the electron mobility of InAsP and InGaAsP can be expected to be faster, it is also possible to expect an improvement in responsiveness at the same film thickness.

[0160] [Other Modifications]

[0161] The above embodiment is an explanation of one aspect of the present invention. Therefore, the semiconductor light receiving element of the present invention can arbitrarily change the semiconductor light receiving elements 1, 1A, 1B, and 1K described above.

[0162] For example, in the semiconductor light-receiving elements 1, 1A, and 1B, the buffer layer 21 is not limited to InAsP, and may contain InGaAsP (or may be composed of InGaAsP) in order to increase the band gap and improve 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.

[0163] In addition, in the semiconductor light receiving elements 1, 1A, 1B, the buffer layer 21 may include a strain relaxation layer whose lattice constant changes in a manner that approaches the lattice constant of the light absorbing layer 23 as it moves from the substrate 10 to the light absorbing layer 23, 23B. In addition, in the semiconductor light receiving elements 1, 1A, the cover 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. In this case, the contact resistance of the electrode 4 is also reduced.

[0164] In addition, in the case of focusing on the viewpoint of high speed, the light absorption layer 23, 23B can also be applied to a waveguide type semiconductor light receiving element in the semiconductor light receiving element 1, 1A, 1B. 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, in the waveguide type, by adopting the light absorption layer 23, 23B with improved absorptivity, the length of the light receiving surface along the extension direction of the waveguide can be shortened to reduce the capacity. In addition, even with the same thickness, the responsiveness can be improved by increasing the electron flight speed.

[0165] In addition, in the semiconductor light-receiving element 1, 1A, 1B, 1K, for example, after removing the substrate 10 by etching or grinding, the semiconductor stacking part 20, 20A, 20B, 20K may be bonded to a substrate made of an insulator such as quartz or a semi-insulating semiconductor material other than InP (for example, gallium arsenide, etc.). In other words, in the semiconductor light-receiving element 1, the substrate 10 may contain an insulator or a semi-insulating semiconductor and be separately formed from the semiconductor stacking part 20, 20A, 20B, 20K, and the semiconductor stacking part 20, 20A, 20B, 20K may be bonded to the substrate 10 (for example, directly). By manufacturing the semiconductor light-receiving element 1 by separately forming the substrate 10 and the semiconductor stacking part 20, 20A, 20B, 20K and bonding them, it is possible to achieve a larger diameter and suppress costs by embedding optical components with inexpensive materials.

[0166] In addition, when the substrate 10 and the semiconductor stacked parts 20, 20A, 20B, 20K, which are separately constructed, are bonded, direct bonding or bonding using resin can be adopted. When the substrate 10 and the semiconductor stacked parts 20, 20A, 20B, 20K are bonded using resin, there is a possibility that the light in the target wavelength band may be absorbed due to the properties of the resin, but this possibility does not exist in direct bonding.

[0167] In addition, in the semiconductor light-receiving elements 1 , 1A, 1B, and 1K, an MIM structure, electronic devices such as transistors, an optical circuit including a spot size converter, and the like may be further formed on the substrate 10 .

[0168] Furthermore, the structures of the semiconductor light receiving elements 1, 1A, 1B, and 1K can be arbitrarily interchangeably adopted.

[0169] Industrial Applicability

[0170] The present invention provides a semiconductor light-receiving element capable of suppressing degradation of characteristics and achieving high speed.

[0171] Explanation of symbols

[0172] 1, 1A, 1B, 1K...semiconductor light-receiving element, 20, 20A, 20B, 20K...semiconductor stacking portion, 21...buffer layer (strain relief layer, second semiconductor layer, fifth semiconductor layer), 22...capacitance reduction layer, 22B...electron transport layer, 23, 23B, 23K...light absorption layer, 24...capping layer (first semiconductor layer), 24B...diffusion barrier layer (fourth semiconductor layer), 25...contact layer (first semiconductor layer, fourth semiconductor layer), 27A...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 of at least one wavelength band of 1.3 μm band, 1.55 μm band and 1.6 μm band and generating an electrical signal in accordance with the incident light. include: substrate; a semiconductor stacked portion formed on the substrate and including a back surface on the substrate side, a surface on the opposite side to the substrate, and a side surface extending from the back surface to the surface; and a first electrode and a second electrode electrically connected to the semiconductor stacked portion, The semiconductor stacking portion comprises: Contains In x Ga 1-x A light absorbing layer of the first conductivity type of As; The first conductive type optical waveguide layer 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, located on the opposite side of the substrate with respect to the light absorbing layer and bonded to the light absorbing layer; The first electrode is connected to the 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 the second portion of the semiconductor stacked portion that is located on the opposite side of the substrate with respect 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 1.8 μm, The semiconductor light receiving element is of a side-incident type that receives the light incident from the side surface, and the light incident from the side surface reaches the light absorbing layer via the optical waveguide layer.

2. The semiconductor light-receiving element according to claim 1, wherein: The semiconductor stack portion includes the first conductivity type buffer layer provided between the substrate and the light absorbing layer.

3. The semiconductor light-receiving element according to claim 2, 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.

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

5. The semiconductor light-receiving element according to claim 1, wherein: The semiconductor stacking portion comprises: A second semiconductor layer of the first conductivity type disposed between the optical waveguide layer and the light absorbing layer; and The first conductivity type capacity reduction layer has an impurity concentration lower than that of the second semiconductor layer and is provided between the second semiconductor layer and the light absorbing layer.

6. The semiconductor light-receiving element according to claim 4, wherein: The semiconductor stacked portion includes a third semiconductor layer provided between the light absorbing layer and the capping layer and having a band gap between a band gap of the light absorbing layer and a band gap of the capping layer.

7. The semiconductor light-receiving element according to claim 1, wherein: The optical waveguide layer includes a layer made semi-insulating by doping with Fe.

8. The semiconductor light-receiving element according to claim 5, wherein: The capacity reduction 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 optical waveguide layer.

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

10. 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.

11. The semiconductor light-receiving element according to claim 10, 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.

12. 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.

13. A semiconductor light receiving element, wherein: A semiconductor light receiving element for receiving incident light of at least one wavelength band of 1.3 μm band, 1.55 μm band and 1.6 μm band and generating an electrical signal in accordance with the incident light. include: substrate; a semiconductor stacked portion formed on the substrate and having a back surface on the substrate side, a surface on the opposite side to the substrate, and a side surface extending from the back surface to the surface; and a first electrode and a second electrode electrically connected to the semiconductor stacked portion, The semiconductor stacking portion comprises: Contains In x Ga 1-x A second conductivity type light absorbing layer of As; an optical waveguide layer of a first conductivity type different from the second conductivity type provided between the substrate and the light absorbing layer; and the fourth semiconductor layer of the second conductivity type located on the opposite side of the substrate with respect to the light absorbing layer and bonded to the light absorbing layer, The first electrode is connected to the 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 the second portion of the semiconductor stacked portion that is located on the opposite side of the substrate with respect 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 1.8 μm, The semiconductor light receiving element is of a side-incident type that receives the light incident from the side surface, and the light incident from the side surface reaches the light absorbing layer via the optical waveguide layer.

14. The semiconductor light-receiving element according to claim 13, wherein: The semiconductor stack portion includes the first conductivity type buffer layer provided between the substrate and the light absorbing layer.

15. The semiconductor light receiving element according to claim 14, 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.

16. The semiconductor light-receiving element according to claim 13, wherein: The semiconductor stack portion comprises: a diffusion barrier layer of the second conductivity type provided on the light absorbing layer on the side opposite to the substrate with respect to the light absorbing layer and containing InAsP or InGaAsP; and The second conductivity type contact layer is provided on the diffusion barrier layer on the opposite side to the substrate with respect to the light absorbing layer and includes InGaAs, The fourth semiconductor layer includes the contact layer and the diffusion barrier layer, The second portion to which the second electrode is connected is a surface of the contact layer.

17. The semiconductor light-receiving element according to claim 13, wherein: The semiconductor stacking portion comprises: a fifth semiconductor layer of the first conductivity type disposed between the optical waveguide layer and the light absorbing layer; and The first conductivity type electron transport layer has an impurity concentration lower than that of the fifth semiconductor layer and is provided between the fifth semiconductor layer and the light absorbing layer.

18. The semiconductor light receiving element according to claim 16, 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.

19. The semiconductor light-receiving element according to claim 13, wherein: The optical waveguide layer includes a layer made semi-insulating by doping with Fe.

20. The semiconductor light-receiving element according to claim 17, wherein: The electron transport layer has an impurity concentration lower than that of the light absorbing layer and has a band gap larger than that of the light absorbing layer, and is provided between the light absorbing layer and the optical waveguide layer.

21. The semiconductor light-receiving element according to claim 20, wherein: The thickness of the electron transport layer is not less than 0.3 μm and not more than 3.0 μm. The impurity concentration of the electron transport layer is 2.0×10 14 cm -3 Above 3.0×10 16 cm -3 the following.

22. The semiconductor light receiving element according to claim 13, 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.

23. The semiconductor light receiving element according to claim 13, 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.

24. The semiconductor light-receiving element according to claim 13, wherein: The substrate comprises an insulator or a semi-insulating semiconductor, The semiconductor stacked portion is bonded to the substrate.

25. A semiconductor light receiving element, wherein: A semiconductor light receiving element for receiving incident light of at least one wavelength band of 1.3 μm band, 1.55 μm band and 1.6 μm band and generating an electrical signal in accordance with the incident light. include: 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 stacked portion formed on the second region and having a back surface on the substrate side, a surface on the opposite side to the substrate, and a side surface extending from the back surface to the surface; a first semiconductor portion of a first conductivity type formed on the first region; a second semiconductor portion formed on the third region and having a second conductivity type different from the first conductivity type; a first electrode electrically connected to the first semiconductor portion; and a second electrode electrically connected to the second semiconductor portion, The semiconductor stacking portion comprises: Contains In x Ga 1-x As light absorbing layer; and An optical waveguide layer disposed between the substrate and 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 1.8 μm, The semiconductor light receiving element is of a side-incident type that receives the light incident from the side surface, and the light incident from the side surface reaches the light absorbing layer via the optical waveguide layer.

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