Semiconductor light receiving element

Abstract

To provide semiconductor light receiving element capable of high speed.SOLUTION: A semiconductor light receiving element 1 has a substrate 10, a semiconductor stacking section 20, and electrodes 4 and 5 electrically connected to the semiconductor stacking section 20. The semiconductor stacking section 20 includes a light-absorbing layer 23 of the first conductive type including InxGa1-xAs. The In composition x in the light absorbing layer 23 is 0.55 or greater, and the thickness of the light absorbing layer 23 is 0.6 μm to 1.8 μm or less. The semiconductor light receiving element 1 is a side-illuminated type. The width of the light absorbing layer 23 along a direction of incidence of light L with respect to a side surface 20s is 10 μm or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

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

[0002] Patent Document 1 describes an optical waveguide photodetector. This optical waveguide photodetector includes a first semiconductor layer having a first conductivity type, an optical waveguide structure provided on a first region of the first semiconductor layer, and a waveguide photodiode structure provided on a second region of the first semiconductor layer adjacent to the first region. The optical waveguide structure includes an optical waveguide core layer provided on the first semiconductor layer and a cladding layer provided on the optical waveguide core layer. The waveguide photodiode structure includes a light absorption layer provided on the first semiconductor layer and optically coupled to the optical waveguide core layer, the absorption edge of which has a wavelength of 1612 nm or more, and a second semiconductor layer having a second conductivity type provided on the light absorption layer. The length of the light absorption layer in the optical waveguide direction is 12 μm or more. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-117499 Summary of the Invention [Problem to be solved by the invention]

[0004] Meanwhile, in the above technical fields, there is a demand for even faster operating speeds. To achieve this, it is conceivable to shorten the distance that electrons travel by thinning the light absorption layer. However, thinning the light absorption layer results in a decrease in sensitivity. In contrast, in the photodiode described in Patent Document 1, light is incident on the light absorption layer from a direction intersecting the thickness direction of the light absorption layer, thereby increasing the effective thickness of the absorption layer (the light absorption layer has a length of 12 μm in the optical waveguide direction). This is thought to suppress the decrease in sensitivity due to thinning the light absorption layer and thereby achieve an increase in speed. Thus, there is a demand for higher speeds in the above technical fields.

[0005] An object of the present disclosure is to provide a semiconductor light-receiving element that can be made faster. [Means for solving the problem]

[0006] The semiconductor light-receiving element according to the present disclosure is [1] "a semiconductor light-receiving element for receiving incident light of at least one wavelength band selected from the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band, and generating an electrical signal in response to the incident light, the semiconductor light-receiving element comprising: a substrate; a semiconductor laminate portion formed on the substrate, the semiconductor laminate portion including a back surface facing the substrate, a front surface opposite the substrate, and a side surface extending from the back surface toward the front surface; and a first electrode and a second electrode electrically connected to the semiconductor laminate portion, the semiconductor laminate portion comprising In x Ga 1-xa buffer 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 light absorbing layer from the substrate and joined to the light absorbing layer, wherein the first electrode is connected to a first portion of the semiconductor laminate of the first conductivity type located on the substrate side of the light absorbing layer, and the second electrode is connected to a second portion of the semiconductor laminate of the second conductivity type located on the opposite side of the light absorbing layer from the substrate, wherein the In composition x of the light absorbing layer is 0.55 or more, the thickness of the light absorbing layer is 1.8 μm or less, the light absorbing layer is a side incidence type that receives light from the side surface, and the width of the light absorbing layer along the direction of light incidence on the side surface is 10 μm or less.

[0007] The semiconductor photodetector described in [1] above is intended for light in wavelength bands used for optical communications, 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 this semiconductor photodetector, the light absorption layer provided on the substrate is made of In x Ga 1-x The light absorbing layer contains As. The In composition x of the light absorbing layer is 0.55 or more (and less than 1). x Ga 1-x When the In composition x of As is 0.55 or more, the absorption coefficient is improved compared to when the In composition x is 0.53 (for example, in the 1.55 μm band, the absorption coefficient is improved by about two times by setting the composition x to 0.62). Therefore, even if the thickness of the light absorption layer is reduced to about 1.8 μm or less, a decrease in sensitivity can be avoided. This makes it possible to increase speed. Furthermore, for the same reason, the width of the light absorption layer in the incident direction of light can be reduced to 10 μm or less, which reduces the volume of the light absorption layer and enables further speed increase.

[0008] The semiconductor light-receiving element according to the present disclosure may be [2] "the semiconductor light-receiving element according to the above [1], wherein the buffer layer includes a strain relaxation layer having a lattice constant between the lattice constant of the substrate and the lattice constant of the light absorption layer." In this case, the crystallinity of the semiconductor laminate is improved, and an increase in dark current is suppressed.

[0009] The semiconductor light-receiving element according to the present disclosure may be [3] "the semiconductor light-receiving element according to the above [2], in which the buffer layer includes a plurality of strain relaxation layers arranged such that the lattice constant gradually approaches that of the light-absorbing layer from the substrate toward the light-absorbing layer." Alternatively, the semiconductor light-receiving element according to the present disclosure may be [4] "the semiconductor light-receiving element according to the above [2], in which the buffer layer includes a strain relaxation layer whose lattice constant gradually changes such that the lattice constant gradually approaches that of the light-absorbing layer from the substrate toward the light-absorbing layer." In these cases, the crystallinity of the semiconductor laminate portion is reliably improved, and an increase in dark current is suppressed.

[0010] The semiconductor light-receiving element according to the present disclosure may be [5] "the semiconductor light-receiving element according to any one of [1] to [4] above, wherein the semiconductor laminate portion includes: a cap layer of the second conductivity type provided on the light-absorbing layer on the side opposite the substrate with respect to the light-absorbing layer, the cap layer including InAsP or InGaAsP; and a contact layer of the second conductivity type provided on the cap layer on the side opposite the substrate with respect to the light-absorbing layer, the contact layer including InGaAs; the first semiconductor layer includes the contact layer and the cap layer; and the second portion to which the second electrode is connected is the surface of the contact layer." In this case, it is possible to reduce the contact resistance of the second electrode and reduce the series resistance, thereby suppressing deterioration of response. Furthermore, by using a material for the cap layer with a refractive index lower than that of the light-absorbing layer, it is possible to suitably confine light in the light-absorbing layer.

[0011] The semiconductor light-receiving element according to the present disclosure may be [6] "the semiconductor light-receiving element according to any one of the above [1] to [5], wherein the semiconductor laminate portion includes a second semiconductor layer of the first conductivity type disposed between the optical waveguide layer and the light absorption layer, and a capacitance-reducing layer of the first conductivity type disposed between the second semiconductor layer and the light absorption layer, the capacitance-reducing layer having an impurity concentration lower than that of the second semiconductor layer." By providing a capacitance-reducing layer with a relatively low impurity concentration in this way, the capacitance-reducing layer is depleted when a bias is applied, thereby reducing capacitance and thereby achieving further speed increase.

[0012] The semiconductor photodetector according to the present disclosure may be [7] "the semiconductor photodetector according to the above [5], wherein the semiconductor laminate portion includes a third semiconductor layer provided between the light absorption layer and the cap layer, the third semiconductor layer having a bandgap between the bandgap of the light absorption layer and the bandgap of the cap layer." In this case, by providing a layer between the light absorption layer and the cap layer, which has a bandgap therebetween, the barrier between the layers can be reduced, and degradation of response can be suppressed.

[0013] The semiconductor light-receiving element according to the present disclosure may be [8] "the semiconductor light-receiving element according to any one of the above [1] to [7], wherein at least one layer of the buffer layer is semi-insulating by doping with Fe." In this case, it is possible to reduce capacitance.

[0014] The semiconductor light-receiving element according to the present disclosure may be [9] "the semiconductor light-receiving element according to the above [6], wherein the capacitance-reducing layer has an impurity concentration higher than that of the light-absorbing layer, a band gap larger than that of the light-absorbing layer, and is provided between the light-absorbing layer and the optical waveguide layer." In this case, the capacitance-reducing layer has a relatively low impurity concentration as described above and contributes to capacitance reduction. However, simply lowering the impurity concentration of the capacitance-reducing layer increases the barrier between the layers, which may lead to a deterioration in response. On the other hand, increasing the impurity concentration of the capacitance-reducing layer prevents the depletion layer from expanding, making it difficult to sufficiently reduce capacitance. Therefore, as in this case, by lowering the impurity concentration of the capacitance-reducing layer while at least ensuring that the capacitance-reducing layer has a band gap larger than that of the light-absorbing layer, light absorption in the capacitance-reducing layer and carrier generation in the capacitance-reducing layer due to light absorption are suppressed, thereby suppressing a deterioration in response. Furthermore, since the capacitance-reducing layer has a larger band gap than the light-absorbing layer, and also has a higher impurity concentration than the light-absorbing layer, the barrier in the capacitance-reducing layer is reduced.

[0015] The semiconductor light-receiving element according to the present disclosure is

[10] "the capacitance-reducing layer has a thickness of 0.3 μm or more and 3.0 μm or less, and an impurity concentration of the capacitance-reducing layer is 2.0×10 14 cm -3 Over 3.0 x 10 16 cm -3 The semiconductor light-receiving element may be the semiconductor light-receiving element described in [6] or [9] above, which is as follows: In this case, by setting the upper limit of the impurity concentration of the capacitance-reducing layer as described above, it is possible to achieve favorable depletion when a bias is applied. Furthermore, by setting the thickness of the capacitance-reducing 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.

[0016] The semiconductor light-receiving element according to the present disclosure may be

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

[10] above, in which the In composition x in the light-absorbing layer is 0.57 or more, and the thickness of the light-absorbing layer is 1.2 μm or less." Furthermore, the semiconductor light-receiving element according to the present disclosure may be

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

[11] above, in which the In composition x in the light-absorbing layer is 0.59 or more, and the thickness of the light-absorbing layer is 0.7 μm or less." In these cases, a higher speed can be achieved by further thinning the light-absorbing layer.

[0017] The semiconductor light-receiving element according to the present disclosure may be

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

[12] , wherein the substrate includes a semi-insulating semiconductor." In this case, by providing the pad of the first electrode on the substrate, the pad capacitance can be reduced, enabling higher speeds.

[0018] The semiconductor photodetector according to the present disclosure may be

[14] "the semiconductor photodetector according to any one of the above [1] to

[13] , wherein the substrate includes an insulator or a semi-insulating semiconductor, and the semiconductor laminate is bonded to the substrate." In this case, by constructing the semiconductor photodetector by separately constructing the substrate and the semiconductor laminate and directly bonding them, it is possible to increase the diameter and reduce costs by fabricating optical components using inexpensive materials.

[0019] The semiconductor light-receiving element according to the present disclosure is

[15] "a semiconductor light-receiving element for receiving incident light of at least one wavelength band selected from the 1.3 μm band, the 1.55 μm band, and the 1.6 μm band, and generating an electrical signal in response to the incident light, the semiconductor light-receiving element comprising: a substrate; a semiconductor laminate portion formed on the substrate, the semiconductor laminate portion including a back surface facing the substrate, a front surface opposite the substrate, and a side surface extending from the back surface toward the front surface; and a first electrode and a second electrode electrically connected to the semiconductor laminate portion, the semiconductor laminate portion comprising In x Ga 1-xa buffer layer of a second conductivity type containing As; a buffer 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 light absorbing layer from the substrate and joined to the light absorbing layer, wherein the first electrode is connected to a first portion of the semiconductor laminate of the first conductivity type located on the substrate side of the light absorbing layer, and the second electrode is connected to a second portion of the semiconductor laminate of the second conductivity type located on the opposite side of the light absorbing layer from the substrate, wherein the In composition x of the light absorbing layer is 0.55 or more, the thickness of the light absorbing layer is 1.8 μm or less, the light absorbing layer is a side incidence type that receives light from the side surface, and the width of the light absorbing layer along the direction of light incidence on the side surface is 10 μm or less.

[0020] The semiconductor photodetector described in

[15] above is intended for light in wavelength bands used in optical communications, 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 this semiconductor photodetector, the light absorption layer provided on the substrate is made of In x Ga 1-x The light absorbing layer contains As. The In composition x of the light absorbing layer is 0.55 or more (and less than 1). x Ga 1-x When the In composition ratio x of As is 0.55 or more, the absorption coefficient is improved compared to when the In composition ratio x is 0.53 (for example, in the 1.55 μm band, the absorption coefficient is improved by about two times by setting the composition ratio x to 0.62). Therefore, even if the thickness of the light absorption layer is reduced to about 1.8 μm or less, a decrease in sensitivity can be avoided. Furthermore, for the same reason, the width of the light absorption layer in the incident direction of light can be reduced to 10 μm or less, which reduces the capacitance of the light absorption layer and enables further speed increase.

[0021] The semiconductor light-receiving element according to the present disclosure may be

[16] "the semiconductor light-receiving element according to the above

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

[0022] The semiconductor light-receiving element according to the present disclosure may be

[17] "the semiconductor light-receiving element according to the above

[16] , in which the buffer layer includes a plurality of strain relaxation layers arranged such that the lattice constant gradually approaches that of the light-absorbing layer from the substrate toward the light-absorbing layer." Alternatively, the semiconductor light-receiving element according to the present disclosure may be

[18] "the semiconductor light-receiving element according to the above

[16] , in which the buffer layer includes a strain relaxation layer whose lattice constant gradually changes such that the lattice constant gradually approaches that of the light-absorbing layer from the substrate toward the light-absorbing layer." In these cases, the crystallinity of the semiconductor laminate portion is reliably improved, and an increase in dark current is suppressed.

[0023] The semiconductor light-receiving element according to the present disclosure may be

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

[15] to

[18] above, wherein the semiconductor laminate portion includes: a diffusion block layer of the second conductivity type provided on the light-absorbing layer on the side opposite the substrate with respect to the light-absorbing layer, the diffusion block layer containing InAsP or InGaAsP; and a contact layer of the second conductivity type provided on the diffusion block layer on the side opposite the substrate with respect to the light-absorbing layer, the contact layer containing InGaAs; the fourth semiconductor layer includes the contact layer and the diffusion block layer; and the second portion to which the second electrode is connected is the surface of the contact layer." In this case, it is possible to reduce the contact resistance of the second electrode and reduce the series resistance, thereby suppressing deterioration of response. Furthermore, by using a material for the diffusion block layer with a refractive index lower than that of the light-absorbing layer, it is possible to suitably confine light in the light-absorbing layer.

[0024] The semiconductor photodetector according to the present disclosure may be

[20] "the semiconductor photodetector according to any one of

[15] to

[19] above, wherein the semiconductor laminate includes a first conductivity type electron transit layer provided between the buffer layer and the light absorption layer, and the impurity concentration of the electron transit layer is lower than the impurity concentration of the buffer layer." By relatively lowering the impurity concentration of the electron transit layer in this way, the electron transit layer is depleted when a bias is applied, thereby reducing capacitance and achieving further speed increase.

[0025] The semiconductor photodetector according to the present disclosure may be

[21] "the semiconductor photodetector according to the above

[19] , wherein the semiconductor laminate includes a sixth semiconductor layer provided between the light absorption layer and the diffusion blocking layer, the sixth semiconductor layer having a bandgap between the bandgap of the light absorption layer and the bandgap of the diffusion blocking layer." In this case, by providing a layer between the light absorption layer and the cap layer having a bandgap therebetween, the barrier between the layers can be reduced, and degradation of response can be suppressed.

[0026] The semiconductor light-receiving element according to the present disclosure may be

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

[15] to

[21] , wherein at least one of the buffer layers includes a layer that is semi-insulating by doping with Fe." In this case, it is possible to reduce capacitance.

[0027] The semiconductor photodetector according to the present disclosure may be

[23] "the semiconductor photodetector according to the above

[20] , wherein the electron transit layer has an impurity concentration lower than that of the light absorption layer and a band gap larger than that of the light absorption layer, and is disposed between the light absorption layer and the optical waveguide layer." In this case, the capacitance can be reduced by relatively lowering the impurity concentration of the electron transit layer. Furthermore, lowering the impurity concentration of the electron transit layer facilitates depletion and also reduces the barrier between the electron transit layer and the light absorption layer.

[0028] The semiconductor light-receiving element according to the present disclosure is

[24] "the thickness of the electron transit layer is 0.3 μm or more and 3.0 μm or less, and the impurity concentration of the electron transit layer is 2.0 × 10 14 cm -3 Over 3.0 x 10 16 cm -3 The semiconductor photodetector may be the semiconductor photodetector according to the above item

[20] or

[23] , wherein the upper limit of the impurity concentration of the electron transit layer is set as described above, thereby enabling the electron transit layer to be depleted appropriately when a bias is applied. Furthermore, by setting the thickness of the electron transit layer within the above range, it is possible to suppress a decrease in response speed and an increase in the series resistance of the semiconductor photodetector.

[0029] The semiconductor photodetector according to the present disclosure may be

[25] "the semiconductor photodetector according to any one of the above

[15] to

[24] , in which the In composition x in the light absorbing layer is 0.57 or more, and the thickness of the light absorbing layer is 0.3 μm or less." Furthermore, the semiconductor photodetector according to the present disclosure may be

[26] "the semiconductor photodetector according to any one of the above

[15] to

[25] , in which the In composition x in the light absorbing layer is 0.59 or more, and the thickness of the light absorbing layer is 0.1 μm or less." In these cases, a higher speed can be achieved by further thinning the light absorbing layer.

[0030] The semiconductor light-receiving element according to the present disclosure may be

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

[15] to

[26] above, wherein the substrate includes a semi-insulating semiconductor." In this case, by providing the pad of the first electrode on the substrate, the pad capacitance can be reduced, enabling higher speeds.

[0031] The semiconductor photodetector according to the present disclosure may be

[28] "the semiconductor photodetector according to any one of

[15] to

[27] above, wherein the substrate includes an insulator or a semi-insulating semiconductor, and the semiconductor laminate is bonded to the substrate." In this case, by constructing the semiconductor photodetector by separately constructing the substrate and the semiconductor laminate and directly bonding them, it is possible to increase the diameter and reduce costs by fabricating optical components using inexpensive materials.

[0032] The semiconductor light-receiving element according to the present disclosure is

[29] "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 response to the incident light, the semiconductor light-receiving element comprising: a substrate having a main surface including a first region, a second region, and a third region arranged in order along a first direction; a semiconductor laminate portion formed on the second region and including a back surface facing the substrate, a front surface opposite to the substrate, and a side surface extending from the back surface toward the front surface; a first semiconductor portion of a first conductivity type formed on the first region; a second semiconductor portion of a second conductivity type different from the first conductivity type formed on the third region; a first electrode electrically connected to the first semiconductor portion; a second electrode electrically connected to the second semiconductor portion; and an optical waveguide formed on the second region, extending along the main surface and along a second direction intersecting the first direction toward the side surface and coupled to the side surface, the semiconductor laminate portion comprising: In x Ga 1-x a semiconductor light-receiving element including a light-absorbing layer containing As, wherein the In composition x in the light-absorbing layer is 0.55 or more, the thickness of the light-absorbing layer is 1.8 μm or less, the light-absorbing layer is a side-incident type that receives the light from the side surface via the optical waveguide, and the width of the light-absorbing layer along the direction of incidence of the light on the side surface is 10 μm or less.

[0033] The semiconductor photodetector described in

[29] above is intended for light in wavelength bands used in optical communications, 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 this semiconductor photodetector, the light absorption layer provided on the substrate is made of In x Ga 1-x The light absorbing layer contains As. The In composition x of the light absorbing layer is 0.55 or more (and less than 1). x Ga 1-xWhen the In composition ratio x of As is 0.55 or more, the absorption coefficient is improved compared to when the In composition ratio x is 0.53 (for example, in the 1.55 μm band, the absorption coefficient is improved by about two times by setting the composition ratio x to 0.62). Therefore, even if the thickness of the light absorption layer is reduced to about 1.8 μm or less, a decrease in sensitivity can be avoided. Furthermore, for the same reason, the width of the light absorption layer in the incident direction of light can be reduced to 10 μm or less, which reduces the capacitance of the light absorption layer and enables further speed increase. [Effects of the Invention]

[0034] According to the present disclosure, it is possible to provide a semiconductor light receiving element that can achieve high speed. [Brief explanation of the drawings]

[0035] [Figure 1] FIG. 1 is a schematic plan view showing a semiconductor light receiving element according to the first embodiment. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. [Figure 3] FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. [Figure 4] FIG. 4 is a graph illustrating the relationship between the composition of the light absorption layer and the absorption coefficient. [Figure 5] FIG. 5 is a schematic cross-sectional view of the semiconductor light receiving element according to the second embodiment. [Figure 6] FIG. 6 is a schematic cross-sectional view of a semiconductor light-receiving element according to the third embodiment. [Figure 7] FIG. 7 is a schematic cross-sectional view of a semiconductor light-receiving element according to the fourth embodiment. [Figure 8] FIG. 8 is a schematic cross-sectional view of a semiconductor light-receiving element according to the fifth embodiment. [Figure 9] FIG. 9 is a schematic plan view of the semiconductor light receiving element according to the sixth embodiment. [Figure 10] FIG. 10 is a schematic cross-sectional view taken along line XX in FIG. [Figure 11]FIG. 11 is a schematic cross-sectional view taken along line XI-XI in FIG. [Figure 12] FIG. 12 is a cross-sectional view showing a modification of the semiconductor light-receiving element shown in FIG. [Figure 13] FIG. 13 is a schematic cross-sectional view of the semiconductor light-receiving element according to the seventh embodiment. [Figure 14] FIG. 14 is a schematic cross-sectional view of the semiconductor light-receiving element according to the seventh embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0036] An embodiment will be described in detail below with reference to the drawings. In each drawing, the same or corresponding elements are designated by the same reference numerals, and redundant description may be omitted. [First embodiment]

[0037] FIG. 1 is a schematic plan view showing a semiconductor light receiving element according to a first embodiment. FIG. 2 is a schematic cross-sectional view taken along line II-II in FIG. 1. FIG. 3 is a schematic cross-sectional view taken along line III-III in FIG. 1. The semiconductor light receiving element 1 shown in FIGS. 1 to 3 is intended for light in wavelength bands used for optical communications, 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)). That is, the semiconductor light receiving element 1 receives light in at least one of the above wavelength bands and generates an electrical signal in response to the incident light. The 1.3 μm band is, for example, a wavelength range of 1.26 μm to 1.36 μm. The 1.55 μm band is, for example, a wavelength range of 1.53 μm to 1.565 μm. The 1.6 μm band is, for example, a wavelength range greater than 1.565 μm and equal to or less than 1.625 μm. Furthermore, light in a wavelength band for communications is light having a peak within the wavelength range of any of the above wavelength bands (i.e., wavelengths other than the peak may be outside the wavelength range of the above wavelength bands).

[0038] The semiconductor light receiving element 1 includes a substrate 10, a semiconductor laminate 20, an electrode 4 (second electrode), and a pair of electrodes 5 (first electrodes). The electrode 4 includes a bonding portion 4a bonded to the semiconductor laminate 20, a pad portion 4b, and a connection portion 4c connecting the bonding portion 4a and the pad portion 4b. The connection portion 4c increases in width from the bonding portion 4a toward the pad portion 4b. The electrode 5 includes a bonding portion 5a bonded to the semiconductor laminate 20, a pad portion 5b, and a connection portion 5c connecting the bonding portion 5a and the pad portion 5b. The connection portion 5c increases in width from the bonding portion 5a toward the pad portion 5b.

[0039] The substrate 10 includes a semi-insulating semiconductor. Here, the substrate 10 is, for example, a semi-insulating semiconductor substrate made of InP. The substrate 10 includes a front surface (main surface) 10a and a back surface 10b opposite the front surface 10a. The substrate 10 also includes a region RA, a region RB, and a region RC arranged in this order along the X-axis direction (first direction) along the front surface 10a and the back surface 10b. The region RB is between the region RA and the region RC, and is a region where the semiconductor laminate portion 20 is provided.

[0040] As described above, the semiconductor laminate 20 is formed on the region RB of the substrate 10 and is configured as a semiconductor mesa protruding from the surface 10a. The semiconductor laminate 20 includes a back surface 20b on the substrate 10 side, a front surface 20a on the opposite side from the substrate 10, and a side surface 20s extending from the back surface 20b toward the front surface 20a. The side surface 20s connects the back surface 20b and the front surface 20a. The semiconductor laminate 20 includes a buffer layer 21, a capacitance-reducing layer 22, a light-absorbing layer 23, a cap layer 24 (first semiconductor layer), and a contact layer 25 (first semiconductor layer), which are stacked in this order from the substrate 10 side. The front surface 20a is the surface of the contact layer 25 opposite the light-absorbing layer 23, and the back surface 20b is the surface of the buffer layer 21 opposite the light-absorbing layer 23 and is in contact with the front surface 10a of the substrate 10.

[0041] The buffer layer 21 is of a first conductivity type (here, N type, for example, N +The buffer layer 21 is provided across the regions RA and RC, with the region RB at the center. Here, the semiconductor laminate 20 is in contact with the surface 10a of the substrate 10 at the buffer layer 21. The layers of the semiconductor laminate 20 other than the buffer layer 21 are provided on the region RB. That is, the buffer layer 21 has a portion 21p that protrudes from the other layers of the semiconductor laminate 20 when viewed from a direction intersecting the surface 10a, and a bond with the electrode 5 (bonding portion 5a) is formed at this portion 21p.

[0042] The buffer layer 21 includes a first buffer layer, a second buffer layer, and a third buffer layer stacked in this order from the substrate 10 side. + The second buffer layer is made of N + -InAs 0.05 The third buffer layer is made of N + -InAs 0.10 Capacitance-reducing layer 22 is made of a first conductivity type (here, N type, for example, N - As an example, N - -InAs 0.15 It consists of P.

[0043] As a result, buffer layer 21 and capacitance-reducing layer 22 function as strain-relieving layers having a lattice constant between that of substrate 10 and that of light-absorbing layer 23. In other words, semiconductor stack 20 includes a plurality of strain-relieving layers (step layers) that are provided so that the lattice constant gradually approaches that of light-absorbing layer 23 from substrate 10 toward light-absorbing layer 23. Buffer layer 21 has a thickness of, for example, 0.5 μm or more and 5 μm or less.

[0044] Furthermore, capacitance-reducing layer 22 is disposed closer to light-absorbing layer 23 than buffer layer 21, and has an impurity concentration lower than the impurity concentration of buffer layer 21. Light-absorbing layer 23 is of a first conductivity type (e.g., N - The light absorbing layer 23 includes InGaAs. Here, the light absorbing layer 23 includes N - -In x Ga 1-xThe light absorbing layer 23 is made of As. The In composition x of the light absorbing layer 23 is 0.55 or more (and less than 1). For example, the In composition x may be 0.57 or more, and here is 0.59 or more (for example, 0.59).

[0045] The thickness of the light absorbing layer 23 (thickness along the stacking direction (Z-axis direction) of the semiconductor stack portion 20) is 0.6 μm or more and 1.8 μm or less. As an example, the thickness of the light absorbing layer 23 may be 1.2 μm or less, and here is 0.7 μm or less (for example, 0.7 μm). The light absorbing layer 23 may be an absorption layer of a mixed crystal of InGaAs with Al, P, Sb, N, or other material, so long as the band gap is in the range of 0.72 eV or less. The ratio of Al, P, Sb, and N (or other material) mixed into InGaAs can be, for example, 5% or less, or 10% or less.

[0046] Here, capacitance-reducing layer 22 has an impurity concentration higher than the impurity concentration of light-absorbing layer 23. For example, the impurity concentration of capacitance-reducing layer 22 is 2.0×10 14 cm -3 Over 3.0 x 10 16 cm -3 The impurity concentration of the light absorbing layer 23 is about 1.0×10 14 cm -3 Over 1.0 x 10 16 cm -3 Furthermore, capacitance-reducing layer 22 has a band gap larger than the band gap of light-absorbing layer 23. When the band gap of light-absorbing layer 23 is 0.72 eV or less as described above, the band gap of capacitance-reducing layer 22 can be in the range of more than 0.72 eV and 1.35 eV or less.

[0047] As a result, semiconductor laminate 20 has capacitance-reducing layer 22 provided between buffer layer 21 and light-absorbing layer 23. As described above, capacitance-reducing layer 22 is required to have a higher impurity concentration than light-absorbing layer 23 and to be depleted when a bias is applied. This is because, as described above, capacitance-reducing layer 22 has a larger band gap than light-absorbing layer 23, and if the impurity concentration is low, a barrier is created in the conduction band, which may hinder the movement of carriers due to the large barrier and prevent them from being suitably extracted.

[0048] Furthermore, capacitance-reducing layer 22 needs to be depleted when a bias is applied, and therefore the upper limit of the impurity concentration is set to 3.0×10 16 cm -3 It is preferable that the composition of capacitance-reducing layer 22 be about that level. Furthermore, it is desirable that capacitance-reducing layer 22 has a composition that does not absorb incident light (i.e., a band gap wider than that of light-absorbing layer 23). This is because if capacitance-reducing layer 22 absorbs incident light, carriers will be generated in capacitance-reducing layer 22. These carriers will be extracted as signals from capacitance-reducing layer 22 via light-absorbing layer 23, and will become slow carriers, which may deteriorate the response characteristics.

[0049] In other words, by setting the relationship between buffer layer 21, capacitance-reducing layer 22, and light-absorbing layer 23 as described above, capacitance-reducing layer 22 can function as a layer that can reduce capacitance without reducing carrier response. Since capacitance-reducing layer 22 is effective as long as it is provided, there are no particular limitations on its thickness, but it can be set to be 0.3 μm or more and 3 μm or less, for example.

[0050] In addition, P - By providing a type semiconductor layer, it is possible to use the semiconductor layer as a capacitance reducing layer. - The semiconductor layer is P - It is easier to fabricate than P type semiconductor layers, -Since electrons have a higher mobility than carriers in the layer, a N - It is believed that forming capacitance-reducing layer 22 of the same type is more effective.

[0051] Furthermore, in the semiconductor light receiving element 1, the light absorbing layer 23 is a single layer. The light absorbing layer 23 being a single layer means that the light absorbing layer 23 does not have a layered structure formed by stacking two or more layers with different compositions or properties. More specifically, the light absorbing layer 23 being a single layer means that it does not have a superlattice structure formed by repeatedly stacking multiple layers with different compositions, for example.

[0052] The cap layer 24 is of a second conductivity type (here, P type, as an example) different from the first conductivity type. + The cap layer 24 includes InAsP or InGaAsP. In this example, the cap layer 24 includes InAsP. As an example, the cap layer 24 includes P + -InAs 0.15 It is made of P. The thickness of the cap layer 24 is, for example, not less than 0.05 μm and not more than 2.5 μm.

[0053] The contact layer 25 is of a second conductivity type (here, P type, for example, P + The contact layer 25 includes InGaAs. In one example, the contact layer 25 includes P + The contact layer 25 is made of InGaAs. The thickness of the contact layer 25 is, for example, not less than 0.025 μm and not more than 0.2 μm. In this way, the semiconductor laminate 20 includes a first semiconductor layer of the second conductivity type that is located on the opposite side of the light absorption layer 23 from the substrate 10 and is joined to the light absorption layer 23. The first semiconductor layer includes a cap layer 24 and a contact layer 25.

[0054] In the above example, N + The N-type impurity concentration is 1×10 17 cm -3 It means that the degree is higher than that.- The N-type impurity concentration is 3.0×10 16 cm -3 This means that the level is relatively low compared to the N+ type. + The P-type impurity concentration is 1×10 17 cm -3 It means that it is more than the same.

[0055] 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 laminate 20 and a side surface 20s of the semiconductor laminate 20 extending from the periphery of the surface 20a toward the substrate 10 are covered with the protective film F. On the other hand, the remaining portion of the surface 20a of the semiconductor laminate 20, in this case, a portion of the surface of the contact layer 25, is exposed from an opening Fp in the protective film F.

[0056] A junction 4a of the electrode 4 is formed on a portion of the surface 20a exposed from the protective film F, thereby forming a junction between the electrode 4 and the semiconductor laminate 20 (contact layer 25). That is, the electrode 4 is connected to a second portion of the semiconductor laminate 20 (here, the surface of the contact layer 25) of the second conductivity type located on the opposite side of the light absorption layer 23 from the substrate 10. Meanwhile, a part 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 junction 5a of the electrode 5 is formed on the exposed portion, thereby forming a junction between the electrode 5 and the semiconductor laminate 20 (buffer layer 21). That is, the electrode 5 is connected to a first portion of the semiconductor laminate 20 of the first conductivity type (the surface of the buffer layer 21) located on the substrate 10 side of the light absorption layer 23.

[0057] Here, the semiconductor light-receiving element 1 has a light-receiving section 2 including the semiconductor laminate 20 described above, and a waveguide section 3 that propagates light toward the light-receiving section 2. The waveguide section 3 includes a buffer layer 21 and a capacitance-reducing layer 22 provided on the front surface 10a of the substrate 10. More specifically, the buffer layer 21 and the capacitance-reducing layer 22 extend outside the light-receiving section 2 (the semiconductor laminate 20) along the Y-axis direction (a second direction intersecting the first direction) along the front surface 10a and the back surface 10b of the substrate 10, respectively, and the waveguide section 3 is formed by the portions of the buffer layer 21 and the capacitance-reducing layer 22 that extend outside the light-receiving section 2.

[0058] In other words, buffer layer 21 includes portion 21q included in semiconductor laminate portion 20 and portion 21r extending from side surface 20s of semiconductor laminate portion 20 to the outside of semiconductor laminate portion 20, and capacitance-reducing layer 22 includes portion 22q included in semiconductor laminate portion 20 and portion 22r extending from side surface 20s of semiconductor laminate portion 20 to the outside of semiconductor laminate portion 20. Portions 21r and 22r form the waveguide portion 3. The surface of portion 22r opposite to the substrate 10 is covered with protective film F.

[0059] The semiconductor light-receiving element 1 is a side-incidence type in which light L guided by the buffer layer 21 and capacitance-reducing layer 22 in the waveguide portion 3 is incident from a side surface 20s of the semiconductor laminate portion 20. Therefore, in the semiconductor light-receiving element 1, the buffer layer 21 and capacitance-reducing layer 22 also serve as a first conductivity type optical waveguide layer provided between the substrate 10 and the light-absorbing layer 23. The refractive indexes of the buffer layer 21, capacitance-reducing layer 22, and light-absorbing layer 23 increase in this order.

[0060] Therefore, light L propagating through the waveguide portion 3 is distributed mainly in the capacitance-reducing layer 22, enters the semiconductor laminate portion 20 from the side surface 20s of the semiconductor laminate portion 20, transitions from the buffer layer 21 and capacitance-reducing layer 22 side to the light-absorbing layer 23, and is absorbed in the light-absorbing layer 23. That is, the semiconductor light-receiving element 1 is a side-incident type. The light L incident from the side surface 20s reaches the light-absorbing layer 23 via the optical waveguide layer. The width of the light-absorbing layer 23 along the incident direction of the light L to the side surface 20s (the Y-axis direction) is, for example, 2 μm or more and 10 μm or less. Note that by making the refractive index of the light-absorbing layer 23 lower than the refractive index of the cap layer 24, it is possible to suitably confine the light L within the light-absorbing layer 23. Furthermore, the refractive index of the substrate 10 is preferably lower than that of the buffer layer 21, but may be higher than that of the buffer layer 21.

[0061] As described above, the semiconductor light receiving element 1 is intended for light in wavelength bands used 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 absorption layer 23 provided on the substrate 10 is made of In x Ga 1-x The light absorbing layer 23 contains As. The In composition x of the light absorbing layer 23 is 0.55 or more (and less than 1). x Ga 1-x When the In composition x of As is 0.55 or more (graph G2 in Fig. 4), the absorption coefficient is improved (about twice as much in the 1.55 μm band) compared to when the In composition x is 0.53 as shown in graph G1 in Fig. 4. Graph G0 in Fig. 4 shows the case where a light absorption layer made of InGaAsP is used.

[0062] Therefore, even if the thickness of the light-absorbing layer 23 is reduced to approximately 1.8 μm or less, a decrease in sensitivity is avoided. In other words, higher speeds are possible. Furthermore, the semiconductor light-receiving element 1 is a side-incident type in which light enters the semiconductor laminate 20 from the side surface 20s of the semiconductor laminate 20. However, the light incident from the side surface 20s reaches the light-absorbing layer 23 via an optical waveguide layer (at least the capacitance-reducing layer 22) located closer to the substrate 10 than 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, which intersects with the thickness of the light-absorbing layer 23. This increases the area in the light-absorbing layer 23 where light is absorbed, compared to when light is directly incident from an end face of the light-absorbing layer in the Y-axis direction. As a result, a local increase in photocarrier density does not occur, and deterioration of characteristics such as frequency response and linearity is suppressed. Therefore, the semiconductor light-receiving element 1 enables higher speeds while suppressing deterioration of characteristics. Furthermore, according to the semiconductor light receiving element 1, the width of the light absorbing layer 23 in the incident direction of light can be set to 10 μm or less while avoiding a decrease in sensitivity, and the capacitance of the light absorbing layer 23 can be reduced to achieve even higher speeds.

[0063] Furthermore, in the semiconductor light receiving element 1, the semiconductor laminate 20 includes a first conductivity type buffer layer 21 provided between the substrate 10 and the light absorbing layer 23. Therefore, by increasing the impurity concentration of the buffer layer 21, it is possible to suitably use the buffer layer 21 for forming contact with the electrode 5. Furthermore, by providing the buffer layer 21 below the light absorbing layer 23, it is possible to suppress deterioration of response.

[0064] Furthermore, in the semiconductor light receiving element 1, the buffer layer 21 includes strain relaxation layers (first to third buffer layers) having a lattice constant between the lattice constant of the substrate 10 and the lattice constant of the light absorption layer 23. This improves the crystallinity of the semiconductor laminate portion 20 and suppresses an increase in dark current.

[0065] Furthermore, in the semiconductor light receiving element 1, the buffer layer 21 includes a plurality of strain relaxation layers (first to third buffer layers) that are provided so that the lattice constants gradually approach the lattice constant of the light absorbing layer 23 from the substrate 10 toward the light absorbing layer 23. This reliably improves the crystallinity of the semiconductor laminate portion and suppresses an increase in dark current.

[0066] In the semiconductor light-receiving element 1, the semiconductor laminate 20 includes a cap layer 24 (first semiconductor layer) of a second conductivity type that is provided on the light-absorbing layer 23 on the side opposite the substrate 10 with respect to the light-absorbing layer 23 and that contains InAsP, and a contact layer 25 (first semiconductor layer) of the second conductivity type that is provided on the cap layer 24 on the side opposite the substrate 10 with respect to the light-absorbing layer 23 and that contains InGaAs. The second portion to which the electrode 4 is connected is the surface of the contact layer 25. This reduces the contact resistance of the electrode 4 and the series resistance, thereby preventing a deterioration in response. Furthermore, by using a material for the cap layer 24 that has a refractive index lower than that of the light-absorbing layer 23, it is possible to suitably confine light in the light-absorbing layer 23.

[0067] Furthermore, in the semiconductor light receiving element 1, the semiconductor laminate 20 is disposed between the substrate 10 (buffer layer 21) and the light absorbing layer 23, and includes a capacitance-reducing layer 22 of the first conductivity type having an impurity concentration lower than the impurity concentration of the buffer layer 21. By providing capacitance-reducing layer 22 having a relatively low impurity concentration in this manner, capacitance-reducing layer 22 is depleted when a bias is applied, thereby reducing capacitance and achieving further speed increase.

[0068] In addition, in semiconductor light receiving element 1, capacitance-reducing layer 22 has a higher impurity concentration than light-absorbing layer 23 and a larger band gap than light-absorbing layer 23, and is provided between light-absorbing layer 23 and buffer layer 21. As described above, capacitance-reducing layer 22 has a relatively low impurity concentration and contributes to capacitance reduction. However, simply lowering the impurity concentration of capacitance-reducing layer 22 may increase the barrier between the layers, potentially leading to response degradation. On the other hand, increasing the impurity concentration of capacitance-reducing layer 22 may prevent the depletion layer from expanding, making it difficult to sufficiently reduce capacitance.

[0069] Therefore, as described above, when the impurity concentration of capacitance-reducing layer 22 is reduced, capacitance-reducing layer 22 is made to have a larger band gap than light-absorbing layer 23, thereby suppressing light absorption in capacitance-reducing layer 22 and the generation of carriers in capacitance-reducing layer 22 due to the light absorption, and thereby suppressing deterioration of response. Furthermore, because capacitance-reducing layer 22 has a larger band gap than light-absorbing layer 23 and a higher impurity concentration than light-absorbing layer 23, the barrier in capacitance-reducing layer 22 is reduced.

[0070] In semiconductor light-receiving element 1, capacitance-reducing layer 22 has a thickness of 0.3 μm or more and 3.0 μm or less, and an impurity concentration of capacitance-reducing layer 22 is 2.0×10 14 cm -3 Over 3.0 x 10 16 cm -3 Therefore, by setting the upper limit of the impurity concentration of capacitance-reducing layer 22 as described above, it is possible to achieve favorable depletion when a bias is applied. Furthermore, by setting the thickness of capacitance-reducing layer 22 within the above range, it is possible to suppress a decrease in response speed and an increase in the series resistance of semiconductor light-receiving element 1.

[0071] In the semiconductor light receiving element 1, the In composition x of 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 of 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, further thinning of the light absorbing layer 23 can achieve higher speeds.

[0072] Furthermore, in the semiconductor light-receiving element 1, the substrate 10 includes a semi-insulating semiconductor. Therefore, by providing the pad portion 5b of the electrode 5 on the substrate 10, the pad capacitance can be reduced, enabling an increase in speed.

[0073] In the semiconductor light-receiving element 1, the buffer layer 21 constitutes at least a part of the optical waveguide layer, but may also include a layer that is semi-insulating due to Fe doping, which can reduce capacitance.

[0074] Furthermore, in the semiconductor light receiving element 1, the semiconductor laminate 20 may include a third semiconductor layer provided between the light absorbing layer 23 and the capping layer 24, the third semiconductor layer having a bandgap between the bandgap of the light absorbing layer 23 and the bandgap of the capping layer 24. In this case, by providing a layer between the light absorbing layer 23 and the capping layer 24, which has a bandgap therebetween, the barrier between the layers can be reduced, and response degradation can be suppressed.

[0075] The following lists examples of combinations of each wavelength band with the thickness of the light absorbing layer 23 and the In composition x of the light absorbing layer 23. For example, the following (5) can be configured not only for the C-band but also for the O-band and the L-band.

[0076] (1) C-band. Sensitivity: 0.86A / W or more. Cutoff frequency: 20GHz or higher (for 28GB etc.). Absorbing layer thickness: 1.5 μm. In composition x:x=0.55.

[0077] (2) C-band. Sensitivity: 0.90A / W or more. Cutoff frequency: 20GHz or higher (for 28GB high sensitivity products). Absorbing layer thickness: 1.5 μm. In composition x:x=0.57.

[0078] (3) C-band. Sensitivity: 0.80A / W or more. Cutoff frequency: 30GHz or higher (for 56GB etc.). Absorbing layer thickness: 1.2 μm. In composition x:x=0.57.

[0079] (4) C-band. Sensitivity 0.85A / W or more. Cutoff frequency: 30GHz or higher (for 56GB high sensitivity products). Absorbing layer thickness: 1.2 μm. In composition x:x=0.59.

[0080] (5) C-band. Sensitivity 0.7A / W or more. Cutoff frequency: 45GHz or higher (for 96GB etc.). Absorbing layer thickness: 0.7 μm. In composition x:x=0.59.

[0081] (6) C-band. Sensitivity 0.90A / W or more. Cutoff frequency: 16GHz or higher (for 25GB etc.). Absorbing layer thickness: 1.8 μm. In composition x:x=0.55.

[0082] (7) C-band. Sensitivity 0.93A / W or more. Cutoff frequency: 16GHz or higher (for 25GB etc.). Absorbing layer thickness: 1.8 μm. In composition x:x=0.57. [Second embodiment]

[0083] 5 is a schematic cross-sectional view of a semiconductor light receiving element according to the second embodiment. As shown in FIG. 5, the semiconductor light receiving element 1A differs from the semiconductor light receiving element 1 according to the first embodiment in that it includes a semiconductor laminate 20A instead of the semiconductor laminate 20. The semiconductor laminate 20A further includes an optical waveguide layer 27A in addition to the layers of the semiconductor laminate 20. The optical waveguide layer 27A is provided between the light absorption layer 23 and the substrate 10, more specifically, between the buffer layer 21 and the substrate 10.

[0084] The optical waveguide layer 27A is in contact with the surface 10a of the substrate 10. In the semiconductor light-receiving element 1A, the refractive index increases in the order of the optical waveguide layer 27A, the buffer layer 21, the capacitance-reducing layer 22, and the light-absorbing layer 23. The optical waveguide layer 27A includes, for example, InGaAsP. The optical waveguide layer 27A may be made of a material that does not contain a dopant (e.g., an undoped material) to reduce optical loss. Alternatively, the optical waveguide layer 27A may be made of an insulating material for the same reason. Note that the refractive index of the substrate 10 is preferably lower than that of the optical waveguide layer 27A, but may be higher than that of the optical waveguide layer 27A.

[0085] The optical waveguide layer 27A includes a portion 27q included in the semiconductor laminate 20A and a portion 27r extending from the side surface 20s of the semiconductor laminate 20A to the outside of the semiconductor laminate 20A. The surface of the portion 27r opposite the substrate 10 is covered with a protective film F. In the semiconductor light receiving element 1A, this portion 27r forms the waveguide portion 3. The semiconductor light receiving element 1A is a side incidence type in which light L guided by the optical waveguide layer 27A (portion 27r) in the waveguide portion 3 is received from the side surface 20s of the semiconductor laminate 20A. In the semiconductor light receiving element 1A, light L propagating through the waveguide portion 3 (optical waveguide layer 27A) enters the semiconductor laminate 20A from the side surface 20s of the semiconductor laminate 20A, transitions 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-illumination type. Light L incident from the side surface 20s reaches the light absorption layer 23 via the optical waveguide layer 27A (and the buffer layer 21 and capacitance-reducing layer 22).

[0086] On the other hand, in the semiconductor light receiving element 1A, the buffer layer 21 and the capacitance reducing layer 22 are terminated at the side surface 20s (the end faces of the buffer layer 21 and the capacitance reducing layer 22 are flush with the end face of the light absorbing layer 23) and do not extend outside the side surface 20s. In the semiconductor light receiving element 1A, the semiconductor laminate 20A includes a first conductivity type buffer layer 21 (second semiconductor layer) provided between the optical waveguide layer 27A and the light absorbing layer 23, and a first conductivity type capacitance reducing layer 22 provided between the buffer layer 21 and the light absorbing layer 23, the capacitance reducing layer 22 having an impurity concentration lower than that of the buffer layer 21. The capacitance reducing layer 22 has an impurity concentration higher than that of the light absorbing layer 23 and 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.

[0087] The semiconductor light-receiving element 1A described above can also achieve the same effects as the semiconductor light-receiving element 1. In particular, in the semiconductor light-receiving element 1A, the optical waveguide layer 27A, which is responsible for the propagation of light to the light-receiving section 2, and the buffer layer 21 are configured as separate layers. Therefore, by increasing the impurity concentration of the buffer layer 21, it is possible to suitably use the buffer layer 21 for forming a contact with the electrode 5 without causing optical loss (due to free electron absorption) due to an increase in the impurity concentration of the optical waveguide layer 27A.

[0088] In the semiconductor light receiving element 1A, the semiconductor laminate 20A includes a first conductivity type buffer layer 21 (second semiconductor layer) provided between the optical waveguide layer 27A and the light absorbing layer 23, and a first conductivity type capacitance reducing layer 22 having an impurity concentration lower than that of the buffer layer 21 and provided between the buffer layer 21 and the light absorbing layer 23. By providing the capacitance reducing layer 22 having a relatively low impurity concentration in this way, the capacitance reducing layer 22 is depleted when a bias is applied, thereby achieving a further increase in speed due to the reduction in capacitance. [Third embodiment]

[0089] Fig. 6 is a schematic cross-sectional view of a semiconductor light receiving element according to the third embodiment. As shown in Fig. 6, the semiconductor light receiving element 1B differs from the semiconductor light receiving element 1 according to the first embodiment in that it includes a semiconductor laminate 20B instead of the semiconductor laminate 20. The semiconductor laminate 20B differs from the semiconductor laminate 20 in that it includes an electron transit layer 22B instead of the capacitance reducing layer 22, a light absorbing layer 23B instead of the light absorbing layer 23, and a diffusion blocking layer 24B instead of the cap layer 24.

[0090] The light absorbing layer 23B is In x Ga 1-x Contains As, and is of the second conductivity type (here, P type, as an example, P + The light absorbing layer 23B has an In composition x of 0.55 or more (and less than 1). For example, the In composition x may be 0.57 or more, and here is 0.59 or more (for example, 0.59). The thickness of the light absorbing layer 23B is 1.8 μm or less. For example, the thickness of the light absorbing layer 23B may be 0.3 μm or less, and here may be 0.1 μm or less. For example, the thickness of the light absorbing layer 23B may be 0.02 μm or more and 0.5 μm or less. The width of the light absorbing layer 23B along the incident direction of the light L onto the side surface 20s (the Y-axis direction) is, for example, 2 μm or more and 10 μm or less.

[0091] The electron transit layer 22B is provided between the light absorption layer 23B and the buffer layer 21, and is of a first conductivity type (here, N type, for example, N - The electron transit layer 22B has, for example, an N - -InAs 0.15 The electron transit layer 22B is made of P. The impurity concentration of the electron transit layer 22B is lower than the impurity concentration of the buffer layer 21. The thickness of the electron transit layer 22B is, for example, 0.1 μm to 3.0 μm, and may be 0.3 μm to 3.0 μm. The impurity concentration of the electron transit layer 22B is 2.0×10 14 cm -3 Over 3.0 x 10 16 cm -3 It is about the following.

[0092] The diffusion blocking layer 24B is of a second conductivity type (here, P type, for example, P + The diffusion blocking layer 24B includes InAsP or InGaAsP. In this example, the diffusion blocking layer 24B includes InAsP. As an example, the diffusion blocking layer 24B includes P + -InAs 0.15 The diffusion blocking layer 24B is made of P. The thickness of the diffusion blocking layer 24B is, for example, not less than 0.05 μm and not more than 2.5 μm. In this way, the semiconductor laminate 20B includes a fourth semiconductor layer of the second conductivity type that is located on the opposite side of the light absorbing layer 23B from the substrate 10 and is joined to the light absorbing layer 23B. The fourth semiconductor layer includes the diffusion blocking layer 24B and the contact layer 25.

[0093] In the semiconductor light-receiving element 1B, the buffer layer 21 and the electron transit layer 22B extend outside the semiconductor laminate 20B to form the waveguide 3, similar to the buffer layer 21 and the capacitance-reducing layer 22 of the semiconductor light-receiving element 1. That is, the semiconductor light-receiving element 1B is a side-illuminated element. In the semiconductor light-receiving element 1B, the buffer layer 21 and the electron transit layer 22B also serve as a first-conductivity-type optical waveguide layer provided between the substrate 10 and the light-absorbing layer 23B. In the semiconductor light-receiving element 1B, light L incident from the side surface 20s reaches the light-absorbing layer 23B via the optical waveguide layer.

[0094] The semiconductor photodetector 1B described above can also achieve the same effects as the semiconductor photodetector 1. Furthermore, the UTC structure of the semiconductor photodetector 1B allows for consideration of the movement of electrons only, and improved response can be expected when the light absorption layer 23B is thin. Furthermore, since InAsP and InGaAsP are expected to have faster electron mobility than InP, improved response can also be expected for the same film thickness.

[0095] In the semiconductor light-receiving element 1B, the semiconductor laminate 20B includes a second-conductivity-type diffusion block layer 24B containing InAsP and provided on the light-absorbing layer 23B on the side opposite the substrate 10 from the light-absorbing layer 23B, and a second-conductivity-type contact layer 25 containing InGaAs and provided on the diffusion block layer 24B on the side opposite the substrate 10 from the light-absorbing layer 23B. The fourth semiconductor layer includes the contact layer 25 and the diffusion block layer 24B, and the second portion to which the electrode 4 is connected is the surface of the contact layer 25. This reduces the contact resistance of the electrode 4 and the series resistance, thereby preventing deterioration of response. Furthermore, using a material with a refractive index lower than that of the light-absorbing layer 23B for the diffusion block layer 24B enables light to be suitably confined in the light-absorbing layer 23B.

[0096] In the semiconductor light receiving element 1B, the thickness of the electron transit layer 22B is 0.3 μm or more and 3.0 μm or less, and the impurity concentration of the electron transit layer 22B is 2.0×10 14 cm -3 Over 3.0 x 10 16 cm -3 Therefore, by setting the upper limit of the impurity concentration of the electron transit layer 22B as described above, the electron transit layer 22B can be depleted appropriately when a bias is applied. Furthermore, by setting the thickness of the electron transit layer 22B 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 1B.

[0097] In the semiconductor light receiving element 1B, similarly to the semiconductor light receiving element 1A, the buffer layer 21 and the diffusion blocking layer 24B are terminated at the side surface 20s (the end faces of the buffer layer 21 and the diffusion blocking layer 24B are flush with the end face of the light absorbing layer 23B), and an optical waveguide layer 27A can be provided between the buffer layer 21 and the substrate 10. In this case, the semiconductor laminate 20B includes a first conductivity type buffer layer 21 (fifth semiconductor layer) provided between the optical waveguide layer 27A and the light absorbing layer 23B, and a first conductivity type electron transit 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 relatively lowering the impurity concentration of the electron transit layer 22B in this way, the electron transit layer 22B is depleted when a bias is applied, thereby reducing capacitance and achieving further speed increase.

[0098] In this case, the electron transit layer 22B may have an impurity concentration lower than that of the light absorption layer 23B and a band gap larger than that of the light absorption layer 23B, and may be provided between the light absorption layer 23B and the optical waveguide layer 27A. In this case, the capacitance can be reduced by relatively lowering the impurity concentration of the electron transit layer 22B. Furthermore, lowering the impurity concentration of the electron transit layer 22B facilitates depletion and also reduces the barrier between the electron transit layer 22B and the light absorption layer 23B.

[0099] Furthermore, in the semiconductor light receiving element 1B, the semiconductor laminate 20B may include a sixth semiconductor layer provided between the light absorbing layer 23B and the diffusion blocking layer 24B, the sixth semiconductor layer having a bandgap between the bandgap of the light absorbing layer 23B and the bandgap of the diffusion blocking layer 24B. In this case, by providing a layer between the light absorbing layer 23B and the diffusion blocking layer 24B, which has a bandgap therebetween, the barrier between the layers can be reduced, and response degradation can be suppressed. [Fourth embodiment]

[0100] 7 is a schematic cross-sectional view of a semiconductor light receiving element according to the fourth embodiment. As shown in FIG. 7, the semiconductor light receiving element 1C differs from the semiconductor light receiving element 1 according to the first embodiment in that it further includes an optical waveguide layer 27C and a cladding layer 29C. In the semiconductor light receiving element 1C, like the semiconductor light receiving element 1, the buffer layer 21 includes a portion 21q included in the semiconductor laminate 20 and a portion 21r extending from a side surface 20s of the semiconductor laminate 20 to the outside of the semiconductor laminate 20, but the capacitance-reducing layer 22 terminates at the side surface 20s.

[0101] In the semiconductor light-receiving element 1C, an optical waveguide layer 27C and a cladding layer 29C are stacked in this order on the portion 21r of the buffer layer 21 in the waveguide section 3. The optical waveguide layer 27C has a refractive index higher than at least the refractive index of the buffer layer 21 and the refractive index of the cladding layer 29C. The optical waveguide layer 27C includes, for example, InGaAsP. The optical waveguide layer 27A may be made of a material that does not contain a dopant (e.g., an undoped material) to reduce optical loss. Alternatively, the optical waveguide layer 27C may be made of an insulating material for the same reason.

[0102] The cladding layer 29C may be made of, for example, InP, InAsP, InGaAsP, or the like. The cladding layer 29C has a refractive index lower than that of at least the optical waveguide layer 27C. The surface of the cladding layer 29C opposite to the optical waveguide layer 27C is covered with a protective film F. End faces of the optical waveguide layer 27C and the cladding layer 29C in the optical waveguiding direction (Y-axis direction) are bonded to the side surface 20s of the semiconductor laminate 20. As a result, the optical waveguide layer 27C is optically coupled to the semiconductor laminate 20.

[0103] Here, the thickness of the optical waveguide layer 27C is greater than the sum of the thicknesses of the capacitance-reducing layer 22 and the light-absorbing layer 23. As a result, the optical waveguide layer 27C extends from the interface between the buffer layer 21 and the capacitance-reducing layer 22, over the interface between the light-absorbing layer 23 and the cap layer 24, and into the cap layer 24 in the stacking direction (Z-axis direction) of the semiconductor laminate 20. The refractive index of the light-absorbing layer 23 can be made higher than the refractive indexes of the capacitance-reducing layer 22 and the cap layer 24. As a result, light L that propagates through the optical waveguide layer 27C and enters the semiconductor laminate 20 from the side surface 20s transitions to the light-absorbing layer 23 and is absorbed in the light-absorbing layer 23. In other words, the semiconductor light-receiving element 1C is a side-illuminated type.

[0104] In particular, in the semiconductor light receiving element 1C, the optical waveguide layer 27C and the light absorption layer 23 are directly coupled to each other at the side surface 20s. Therefore, in the semiconductor light receiving element 1C, the light L propagating through the optical waveguide layer 27C is directly incident on the light absorption layer 23 in the incident direction (Y-axis direction) with respect to the side surface 20s. The optical waveguide layer 27C and the cladding layer 29C can be formed by, for example, regrowing a semiconductor layer on the buffer layer 21.

[0105] The semiconductor photodetector 1C described above can also achieve the same effects as the semiconductor photodetector 1, except for the effect that light L incident from the side surface 20s reaches the light absorption layer 23 via the optical waveguide layer. In addition, by arranging the optical waveguide layer 27C directly beside the light absorption layer 23, the influence of light propagation between the core layer and the cladding layer can be reduced. This increases coupling efficiency and enables gain in sensitivity over a short distance.

[0106] In the semiconductor light receiving element 1C, the semiconductor laminate 20 may be changed to a semiconductor laminate 20B, as in the semiconductor light receiving element 1B. In this case, the light absorbing layer 23 is changed to a light absorbing layer 23B of a second conductivity type, and the capacitance reducing layer 22 and the cap layer 24 are changed to an electron transit layer 22B and a diffusion blocking layer 24B, respectively. The relationship between the optical waveguide layer 27C and the cladding layer 29C and each layer is similar. [Fifth embodiment]

[0107] FIG. 8 is a schematic cross-sectional view of a semiconductor light receiving element according to the fifth embodiment. As shown in FIG. 8, the semiconductor light receiving element 1D differs from the semiconductor light receiving element 1 according to the first embodiment in that the side surface 20s of the semiconductor laminate 20 is covered with a protective film F. Therefore, in the semiconductor light receiving element 1D, the end surfaces of all layers of the semiconductor laminate 20 are flush with each other to form the side surface 20s. As a result, in the semiconductor light receiving element 1D, the end surface of the light absorbing layer 23 is exposed through the protective film F, so that light L propagating through, for example, space or an optical fiber can be coupled to the end surface of the light absorbing layer 23 at the side surface 20s. Therefore, the semiconductor light receiving element 1D is a side incidence type in which light L is incident on the side surface 20s of the semiconductor laminate 20. In particular, in the semiconductor light receiving element 1D, light is directly incident on the light absorbing layer 23 in the incident direction (Y-axis direction) relative to the side surface 20s.

[0108] The semiconductor light receiving element 1D described above can also achieve the same effects as the semiconductor light receiving element 1, except for the effect that light L incident from the side surface 20s reaches the light absorbing layer 23 via the optical waveguide layer. Furthermore, by making light directly incident on the light absorbing layer 23, it is not necessary to fabricate the waveguide section 3 on the chip, which makes it possible to minimize the chip size. Furthermore, since no waveguide layer is required, a laminated structure can be considered (for example, by epitaxial growth) with only the core layer (light absorbing layer) and cladding layer, which allows for simplification.

[0109] In the semiconductor light receiving element 1D, the semiconductor laminate 20 may be changed to a semiconductor laminate 20B, similar to the semiconductor light receiving element 1B. In this case, the light absorbing layer 23 is changed to a light absorbing layer 23B of a second conductivity type, and the capacitance reducing layer 22 and the cap layer 24 are changed to an electron transit layer 22B and a diffusion blocking layer 24B, respectively. [Sixth embodiment]

[0110] FIG. 9 is a schematic plan view of a semiconductor light receiving element according to a sixth embodiment. FIG. 10 is a schematic cross-sectional view taken along line XX in FIG. 9. FIG. 11 is a schematic cross-sectional view taken along line XI-XI in FIG. 9. As shown in FIGS. 7 to 9, the semiconductor light receiving element 1K includes a semiconductor laminate 20K provided on the surface 10a of a substrate 10. The surface 10a (main surface) of the substrate 10 includes a first region 10a1, a second region 10a2, and a third region 10a3 arranged in this order along the X-axis direction (first direction). The semiconductor laminate 20K is provided on the second region 10a2.

[0111] The semiconductor light receiving element 1K has a first conductivity type (here, N type, as an example) formed on the first region 10a1. + a first semiconductor portion 41K of a second conductivity type (here, P type, as an example, P + and a second semiconductor portion 42K of a (non-transistor type) type. As a result, a light absorption layer 23K and a semiconductor laminate portion 20K, which will be described later, are disposed between the first semiconductor portion 41K and the second semiconductor portion 42K and are provided so as to be 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 made of, for example, InP, InAsP, or InGaAaP.

[0112] The protective film F covers the surface 20a of the semiconductor laminate 20K. Meanwhile, an opening Fn is provided in the protective film F so as to expose a portion of the surface (top surface) of the first semiconductor portion 41K, and an opening Fp is provided so as to expose a portion of the surface (top surface) of the second semiconductor portion 42K. The electrode 4 (bonding portion 4a) is bonded and electrically connected to the second semiconductor portion 42K through the opening Fp, and the electrode 5 (bonding portion 5a) is bonded and electrically connected to the first semiconductor portion 41K through the opening Fn. Note that contact layers may be provided between the first semiconductor portion 41K and the second semiconductor portion 42K and the electrodes 4 and 5.

[0113] The semiconductor laminate 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 side opposite to the substrate 10. The light absorbing layer 23K is an I-type or a first conductivity type (e.g., N - The light absorbing layer 23K includes InGaAs. Here, the light absorbing layer 23K is an N - -In x Ga 1-x The light absorbing layer 23K is made of As. The In composition x of the light absorbing layer 23K is 0.55 or more (and less than 1). For example, the In composition x may be 0.57 or more, and is 0.59 or more here (for example, 0.59). The thickness of the light absorbing layer 23K is 0.6 μm or more and 1.8 μm or less. For example, the thickness of the light absorbing layer 23K may be 1.2 μm or less, and is 0.7 μm or less here (for example, 0.7 μm). The width of the light absorbing layer 23K along the incident direction of light L to the side surface 20s (Y-axis direction) is, for example, 2 μm or more and 10 μm or less.

[0114] The cladding layer 31K may be made of, for example, InP, InAsP, InGaAsP, or the like. The cladding layer 31K has a refractive index lower than that of the light absorption layer 23K. Here, the surface 20a of the semiconductor laminate 20K is the surface of the cladding layer 31K opposite the light absorption layer 23K. The optical waveguide layer 27K includes, for example, InGaAsP (is made of InGaAsP). The optical waveguide layer 27K may be made of a material that does not contain a dopant (e.g., an undoped material) to reduce optical loss. Alternatively, the optical waveguide layer 27K may be made of an insulating material for the same reason.

[0115] Like the optical waveguide layer 27A, the optical waveguide layer 27K includes a portion 27q that is included in the semiconductor laminate 20K and a portion 27r that extends from the side surface 20s of the semiconductor laminate 20K to the outside of the semiconductor laminate 20K. The surface of the portion 27r opposite to the substrate 10 is covered with a protective film F. In the semiconductor light-receiving element 1K, this portion 27r forms the waveguide portion 3. The semiconductor light-receiving element 1K is a side-incident type in which light L guided by the optical waveguide layer 27K in the waveguide portion 3 is incident from the side surface 20s of the semiconductor laminate 20K.

[0116] In the semiconductor light receiving element 1K, light L propagating through the waveguide 3 (optical waveguide layer 27K) enters the semiconductor laminate 20K from the side surface 20s of the semiconductor laminate 20K, transitions from the optical waveguide layer 27K side to the light absorption layer 23K, and is absorbed in the light absorption layer 23K. That is, the light L incident from the side surface 20s reaches the light absorption layer 23K via the optical waveguide layer 27K. Note that in the semiconductor light receiving element 1K, lattice relaxation can be achieved between the substrate 10 and the light absorption layer 23K in the optical waveguide layer 27K.

[0117] The semiconductor light receiving element 1K described above can also achieve the same effects as the semiconductor light receiving element 1 according to the first embodiment. Furthermore, by using a material with a higher refractive index than the optical waveguide layer 27K and a lower refractive index than the light absorption layer 23K, light can be guided to the absorption layer more efficiently.

[0118] As shown in FIG. 12, the semiconductor light receiving element 1K may be fabricated by directly bonding the semiconductor laminate 20K to a separately prepared substrate after removing the substrate 10 by etching, polishing, or the like. In the example shown in FIG. 12, a substrate 10M including a first layer 51M and a second layer 52M stacked on top of each other is prepared, and the semiconductor laminate 20K is directly bonded to the first layer 51M. In this case, the optical waveguide layer 27K of the semiconductor laminate 20K can be directly bonded to the waveguide 53M formed in the second layer 52M. The first layer 51M and the second layer 52M may contain, for example, SiO2, and the waveguide 53M may contain, for example, Si. By fabricating the semiconductor light receiving element 1K by separately constructing and bonding the substrate 10M and the semiconductor laminate 20K in this manner, a large-area waveguide can be produced inexpensively. [Seventh embodiment]

[0119] Figures 13 and 14 are schematic cross-sectional views of a semiconductor light receiving element according to the seventh embodiment. Figure 13 shows a cross section corresponding to the cross section along line XX in Figure 9 of the sixth embodiment, and Figure 14 shows a cross section corresponding to the cross section along line XI-XI in Figure 9 of the sixth embodiment. The semiconductor light receiving element 1L shown in Figures 13 and 14 differs from the semiconductor light receiving element 1K according to the sixth embodiment in that it includes a semiconductor laminate 20L instead of the semiconductor laminate 20K and in that it includes an optical waveguide layer 32L.

[0120] The semiconductor laminate 20L differs from the semiconductor laminate 20K in that it includes a light absorbing layer 23L instead of the light absorbing layer 23K and a cladding layer 33L instead of the optical waveguide layer 27K. The cladding layer 33L may be made of the same material as the cladding layer 31K. The cladding layer 33L extends beyond the side surface 20s of the semiconductor laminate 20L to the outside of the semiconductor laminate 20L. That is, the cladding layer 33L includes a portion 33q included in the semiconductor laminate 20L and a portion 33r extending from the side surface 20s of the semiconductor laminate 20L to the outside of the semiconductor laminate 20L. The optical waveguide layer 32L is stacked on the portion 33r of the cladding layer 33L outside the semiconductor laminate 20L. The surface of the optical waveguide layer 32L opposite the substrate 10 is covered with a protective film F.

[0121] The light absorbing layer 23L changes the conductivity type of the light absorbing layer 23K to a second conductivity type (for example, P - In the semiconductor light receiving element 1L, a first conductivity type (for example, N - The electron transit layer 43 is provided with a UTC structure. The material of the electron transit layer 43 is the same as that of the electron transit layer 22B. In this way, by adopting a UTC structure, the movement of only electrons is taken into consideration, and improved response is expected when the light absorption layer 23L is thin. Furthermore, since InAsP and InGaAsP are expected to have faster electron mobility than InP, improved response can also be expected for the same film thickness.

[0122] In the semiconductor light receiving element 1L, light L that propagates through the optical waveguide layer 32L and enters the semiconductor laminate 20L from the side surface 20s transitions to the light absorption layer 23L and is absorbed by the light absorption layer 23L. That is, the semiconductor light receiving element 1L is a side-incident type. In particular, in the semiconductor light receiving element 1L, the optical waveguide layer 32L and the light absorption layer 23L are directly coupled to each other at the side surface 20s. Therefore, in the semiconductor light receiving element 1L, the light L that propagates through the optical waveguide layer 32L is directly incident on the light absorption layer 23L in the incident direction (Y-axis direction) relative to the side surface 20s.

[0123] The above-described semiconductor photodetector 1L can also achieve the same effects as the semiconductor photodetector 1, except for the effect of light L incident from the side surface 20s reaching the light absorption layer 23 via the optical waveguide layer. Furthermore, by arranging the optical waveguide layer 32L directly beside the light absorption layer 23L, the influence of light propagation between the core layer and the cladding layer can be reduced. This increases coupling efficiency and increases sensitivity over a short distance.

[0124] In the semiconductor light receiving element 1L, the light absorbing layer 23L may be a light absorbing layer 23K of the first conductivity type, similar to the semiconductor light receiving element 1K. In this case, the electron transit layer 43 may not be provided. In addition, in the semiconductor light receiving element 1K, the conductivity type of the light absorbing layer 23K may be a second conductivity type (for example, P -The electron transit layer 43 may be provided.

[0125] [Other variations]

[0126] The above embodiment has described one aspect of the present disclosure. Therefore, the semiconductor light receiving element according to the present disclosure can be obtained by arbitrarily modifying the above-described semiconductor light receiving elements 1, 1A, 1B, 1C, 1D, 1K, and 1L.

[0127] For example, in the semiconductor light receiving elements 1, 1A, 1B, 1C, and 1D, the buffer layer 21 is not limited to InAsP, but may contain InGaAsP (or may be made of InGaAsP) for the purpose of increasing the band gap and improving the transmittance in the 1.3 μm band, 1.55 μm band, and 1.6 μm band. Furthermore, each layer of the semiconductor laminate portion 20 may contain other elements such as Al.

[0128] Furthermore, in the semiconductor light-receiving elements 1, 1A, 1B, 1C, and 1D, the buffer layer 21 may include a strain relaxation layer whose lattice constant changes continuously from the substrate 10 toward the light-absorbing layer 23, 23B so as to approach the lattice constant of the light-absorbing layer 23. Furthermore, in the semiconductor light-receiving elements 1, 1A, 1C, and 1D, of the cap layer 24 and contact layer 25 stacked in this order on the light-absorbing layer 23, the cap layer 24 may be omitted and the contact layer 25 may be formed directly on the light-absorbing layer 23. Even in this case, the contact resistance of the electrode 4 is reduced.

[0129] Furthermore, when focusing on the viewpoint of increasing speed, the light absorption layers 23 and 23B in the semiconductor light receiving elements 1, 1A, 1B, 1C, and 1D may be applied to a waveguide-type semiconductor light receiving element. In a waveguide-type semiconductor light receiving element, a ridge waveguide is formed on a semi-insulating InP substrate, and a light receiving section including the light absorption layers 23 and 23B is formed within the ridge waveguide. In this way, even in a waveguide-type element, by employing the light absorption layers 23 and 23B with improved absorption, it is possible to shorten the length of the light receiving surface along the extension direction of the waveguide and reduce capacitance. Furthermore, even if the thickness is the same, the response is improved by increasing the electron travel speed.

[0130] Furthermore, in the semiconductor photodetectors 1, 1A, 1B, 1C, 1D, 1K, and 1L, the substrate 10 may be removed by, for example, etching or polishing, and then the semiconductor laminates 20, 20A, 20B, and 20K may be bonded to a substrate made of an insulator such as quartz or a semi-insulating semiconductor other than InP (e.g., gallium arsenide). In other words, in the semiconductor photodetector 1, the substrate 10 may include an insulator or a semi-insulating semiconductor and be configured separately from the semiconductor laminates 20, 20A, 20B, and 20K, and the semiconductor laminates 20, 20A, 20B, and 20K may be bonded (e.g., directly) to the substrate 10. In this way, by manufacturing the semiconductor photodetector 1 by separately configuring and bonding the substrate 10 and the semiconductor laminates 20, 20A, 20B, and 20K, it is possible to increase the diameter and reduce costs by fabricating optical components using inexpensive materials.

[0131] Furthermore, when bonding the substrate 10 and the semiconductor laminated portions 20, 20A, 20B, 20K, and 20L, which are formed separately from each other, direct bonding or bonding using a resin can be adopted. If a resin is used to bond the substrate 10 and the semiconductor laminated portions 20, 20A, 20B, 20K, and 20L, depending on the properties of the resin, there is a possibility that light in the target wavelength band will be absorbed, but this is not possible with direct bonding.

[0132] Furthermore, in the semiconductor light receiving elements 1, 1A, 1B, 1C, 1D, 1K, and 1L, an MIM structure, an electronic device such as a transistor, an optical circuit including a spot size converter, etc. may be further formed on the substrate 10. [Explanation of symbols]

[0133] 1, 1A, 1B, 1C, 1D, 1K, 1L...semiconductor photodetector, 20, 20A, 20B, 20K, 20L...semiconductor laminate portion, 21...buffer layer (strain relaxation layer, second semiconductor layer, fifth semiconductor layer), 22...capacitance reduction layer, 22B...electron transit layer, 23, 23B, 23K, 23L...light absorption layer, 24...cap layer (first semiconductor layer), 24B...diffusion blocking layer (fourth semiconductor layer), 25...contact layer (first semiconductor layer, fourth semiconductor layer), 27A, 27C...optical waveguide layer, 4...electrode (second electrode), 5...electrode (first electrode).

Claims

1. A semiconductor light-receiving element for receiving light in at least one wavelength band selected from the group consisting of a 1.3 μm band, a 1.55 μm band, and a 1.6 μm band, and for generating an electrical signal in response to the incident light, A substrate; a semiconductor laminate portion formed on the substrate, the semiconductor laminate portion including a back surface on the substrate side, a front surface opposite to the substrate, and a side surface extending from the back surface toward the front surface; a first electrode and a second electrode electrically connected to the semiconductor laminate portion; Equipped with The semiconductor laminate portion is In ｘ Ga １－ｘ a first conductivity type light absorbing layer containing As; a buffer layer of the first conductivity type provided between the substrate and the light absorbing layer; a first semiconductor layer of a second conductivity type different from the first conductivity type, which is located on the opposite side of the light absorbing layer from the substrate and is joined to the light absorbing layer; Including, the first electrode is connected to a first portion of the semiconductor laminate portion of the first conductivity type that is located on the substrate side with respect to the light absorption layer, the second electrode is connected to a second portion of the semiconductor laminate that is of the second conductivity type and that is located on the opposite side of the light absorption layer from the substrate, the In composition x in the light absorption layer is 0.55 or more; the thickness of the light absorbing layer is 1.8 μm or less; a side incidence type in which the light is incident from the side surface, a width of the light absorbing layer along the direction of incidence of the light on the side surface is 10 μm or less; Semiconductor photodetector.

2. the buffer layer includes a strain relaxation layer having a lattice constant between the lattice constant of the substrate and the lattice constant of the light absorption layer; 2. The semiconductor light-receiving element according to claim 1.

3. The semiconductor laminate portion is a cap 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, the cap layer including InAsP or InGaAsP; a contact layer of the second conductivity type provided on the cap layer on the opposite side of the substrate with respect to the light absorption layer, the contact layer including InGaAs; Including, 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.

2. The semiconductor light-receiving element according to claim 1.

4. The semiconductor laminate portion is a second semiconductor layer of the first conductivity type disposed between the substrate and the light absorbing layer; a capacitance-reducing layer of the first conductivity type having an impurity concentration lower than an impurity concentration of the second semiconductor layer and disposed between the second semiconductor layer and the light absorbing layer; Including, 2. The semiconductor light-receiving element according to claim 1.

5. the semiconductor laminate portion includes a third semiconductor layer provided between the light absorption layer and the cap layer and having a band gap between a band gap of the light absorption layer and a band gap of the cap layer; 4. The semiconductor light-receiving element according to claim 3.

6. At least one layer of the buffer layer is semi-insulating due to Fe doping.

2. The semiconductor light-receiving element according to claim 1.

7. the capacitance-reducing layer has an impurity concentration higher than an impurity concentration of the light absorbing layer and a band gap larger than a band gap of the light absorbing layer, and is provided between the light absorbing layer and the buffer layer.

5. The semiconductor light-receiving element according to claim 4.

8. the capacitance-reducing layer has a thickness of 0.3 μm or greater and 3.0 μm or less; The capacitance-reducing layer has an impurity concentration of 2.0×10 １４ cm －３ Above 3.0 x 10 １６ cm －３ Below is the 8. The semiconductor light-receiving element according to claim 7.

9. the In composition x in the light absorption layer is 0.57 or more; The thickness of the light absorbing layer is 1.2 μm or less.

2. The semiconductor light-receiving element according to claim 1.

10. the In composition x in the light absorption layer is 0.59 or more; The thickness of the light absorbing layer is 0.7 μm or less. The semiconductor light-receiving element according to claim 9 .

11. the substrate comprises an insulator or a semi-insulating semiconductor; The semiconductor laminate is bonded to the substrate.

2. The semiconductor light-receiving element according to claim 1.

12. A semiconductor light-receiving element for receiving light in at least one wavelength band selected from the group consisting of a 1.3 μm band, a 1.55 μm band, and a 1.6 μm band, and for generating an electrical signal in response to the incident light, A substrate; a semiconductor laminate portion formed on the substrate, the semiconductor laminate portion including a back surface on the substrate side, a front surface opposite to the substrate, and a side surface extending from the back surface toward the front surface; a first electrode and a second electrode electrically connected to the semiconductor laminate portion; Equipped with The semiconductor laminate portion is In ｘ Ga １－ｘ a light absorbing layer of a second conductivity type containing As; a buffer layer of a first conductivity type different from the second conductivity type provided between the substrate and the light absorbing layer; a fourth semiconductor layer of the second conductivity type located on the opposite side of the light absorbing layer from the substrate and joined to the light absorbing layer; Including, the first electrode is connected to a first portion of the semiconductor laminate portion of the first conductivity type that is located on the substrate side with respect to the light absorption layer, the second electrode is connected to a second portion of the semiconductor laminate that is of the second conductivity type and that is located on the opposite side of the light absorption layer from the substrate, the In composition x in the light absorption layer is 0.55 or more; the thickness of the light absorbing layer is 1.8 μm or less; a side incidence type in which the light is incident from the side surface, a width of the light absorbing layer along the direction of incidence of the light on the side surface is 10 μm or less; Semiconductor photodetector.

13. the buffer layer includes a strain relaxation layer having a lattice constant between the lattice constant of the substrate and the lattice constant of the light absorption layer; The semiconductor light-receiving element according to claim 12.

14. The semiconductor laminate portion is a diffusion blocking 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, the diffusion blocking layer including InAsP or InGaAsP; a contact layer of the second conductivity type, the contact layer being provided on the diffusion blocking layer on the opposite side of the substrate from the light absorbing layer, the contact layer including InGaAs; Including, the fourth semiconductor layer includes the contact layer and the diffusion blocking layer; the second portion to which the second electrode is connected is a surface of the contact layer. The semiconductor light-receiving element according to claim 12.

15. the semiconductor laminate portion includes a first conductivity type electron transit layer provided between the buffer layer and the light absorption layer, the impurity concentration of the electron transit layer is lower than the impurity concentration of the buffer layer; The semiconductor light-receiving element according to claim 12.

16. the semiconductor laminate portion includes a sixth semiconductor layer provided between the light absorbing layer and the diffusion blocking layer, the sixth semiconductor layer having a band gap between the band gap of the light absorbing layer and the band gap of the diffusion blocking layer; The semiconductor light-receiving element according to claim 14.

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

18. the electron transit layer has an impurity concentration lower than that of the light absorption layer and a band gap larger than that of the light absorption layer, and is provided between the light absorption layer and the buffer layer; The semiconductor light-receiving element according to claim 15.

19. the thickness of the electron transit layer is 0.3 μm or more and 3.0 μm or less; The impurity concentration of the electron transport layer is 2.0×10 １４ cm －３ Above 3.0 x 10 １６ cm －３ Below is the 19. The semiconductor light-receiving element according to claim 18.

20. the In composition x in the light absorption layer is 0.57 or more; The thickness of the light absorbing layer is 0.3 μm or less. The semiconductor light-receiving element according to claim 12.

21. the In composition x in the light absorption layer is 0.59 or more; The thickness of the light absorbing layer is 0.1 μm or less. The semiconductor light-receiving element according to claim 12.

22. the substrate comprises an insulator or a semi-insulating semiconductor; The semiconductor laminate is bonded to the substrate. The semiconductor light-receiving element according to claim 12.

23. A semiconductor light-receiving element for receiving light in at least one wavelength band selected from the group consisting of a 1.3 μm band, a 1.55 μm band, and a 1.6 μm band, and for generating an electrical signal in response to the incident light, a substrate having a main surface including a first region, a second region, and a third region arranged in order along a first direction; a semiconductor laminate portion formed on the second region and including a back surface on the substrate side, a front surface opposite to the substrate, and a side surface extending from the back surface toward the front 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; a second electrode electrically connected to the second semiconductor portion; an optical waveguide formed on the second region, extending along the main surface and in a second direction intersecting the first direction toward the side surface and coupled to the side surface; Equipped with The semiconductor laminate portion is In ｘ Ga １－ｘ a light absorbing layer containing As, the In composition x in the light absorption layer is 0.55 or more; the thickness of the light absorbing layer is 1.8 μm or less; a side incidence type in which the light is incident from the side surface via the optical waveguide, a width of the light absorbing layer along the direction of incidence of the light on the side surface is 10 μm or less; Semiconductor photodetector.

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