JP2009027046A - Light-receiving element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a light-receiving element which uses an InP substrate, expands sensitivity to a long wavelength side in a near-infrared rays range, and has a GaInNAs light-receiving layer low in dark current. <P>SOLUTION: The light-receiving element includes an InAsP graded buffer layer 20 which is located on the InP substrate 1 and contains arsenic of which the composition ratio is increased step by step in the direction of going away from the InP substrate, a GaInNAs light-receiving layer 3 located on the InAsP graded buffer layer 20, and an InAsP layer located on the GaInNAs light-receiving layer 3. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a light receiving element, and more specifically to a light receiving element having light receiving sensitivity in the near infrared region.

Since the III-V group compound semiconductor using an InP substrate has a band gap energy corresponding to the near-infrared region, many researches are in progress for purposes such as communication, biopsy, and night imaging. One of the most focused efforts is research on how to form a group III-V semiconductor having a smaller band gap energy on a InP substrate with good crystallinity. For example, by using In _0.82 Ga _0.18 As for the light-receiving layer, the band gap is narrowed (the lattice constant is increased) in the group III by decreasing the Ga ratio and increasing the In ratio. An experimental result of a light receiving element with a longer sensitivity wavelength was announced (Non-patent Document 1). When the In ratio is increased as described above, the lattice constant of InGaAs increases, and the lattice mismatch with the InP substrate increases. In the above-described prototype light receiving element, the InP substrate and the high In ratio InGaAs light receiving layer In the meantime, an attempt was made to solve the problem by providing 12 to 20 InAsP graded layers in which the (As / P) ratio was increased stepwise toward the light receiving layer. An increase in lattice mismatch is accompanied by an increase in lattice defect density, which inevitably leads to an increase in dark current. However, the dark current is 20 μA to 35 μA by interposing the above graded buffer layer. .

  Similarly to the above-described concept, the InAsP / P is reduced in order to reduce the lattice mismatch with the InP substrate for the InGaAs light receiving layer whose absorption edge wavelength is increased to about 2 μm by changing the group III composition ratio. There has been proposed a photodiode in which a graded buffer layer of an InAsP strained superlattice layer is interposed (Patent Document 1). It is stated that the InAsP graded layer can be thinned by inserting the strained superlattice.

Further, in InGaAs, a quaternary III-V group semiconductor using a band gap narrowing effect by N has been proposed as GaInNAs by further adding N to a V group element (Patent Document 2).
T.Murakami, H.Takahashi, M.Nakayama, Y.Miura, K.Takemoto, D.Hara, "InxGa1-xAs / InAsyP1-y detector for near infrared (1-2.6μm)", Conference Proceedings of Indium Phosphide and Related Materials JP-A-6-188447 JP-A-9-219563

  However, since the InGaAs layer having a high In composition formed on the InP substrate with the graded buffer layer interposed does not provide perfect lattice matching between the graded buffer layers, the graded buffer layer itself has a lattice defect density. The InGaAs light-receiving layer having a high In composition formed thereon also has a high lattice defect density. Therefore, the dark current is still high. For example, when an imaging apparatus is configured as a two-dimensional array, an increase in dark current due to lattice defects cannot be avoided, a sufficient dynamic range (S / N ratio) cannot be ensured, and the noise level is high. It becomes an image. Further, when a detection device or a spectroscopic analysis device used for detecting a substance is used, only data with low resolution can be obtained for the same reason as described above.

Further, as long as InGaAs is used for the light receiving layer, the absorption edge wavelength is 2.6 μm at the longest, and the sensitivity cannot be extended to longer wavelengths. For this reason, although GaInNAs using N is expected, it is difficult to grow a GaInNAs light-receiving layer having good crystallinity on an InP substrate, and it has not been put into practical use yet. According to the configuration disclosed in Patent Document 2, the GaInNAs light-receiving layer is grown on the InP substrate / InP clad layer so as to be lattice-matched directly. For this reason, in order to make the absorption edge wavelength of the Ga _x In _(1-x) N _y As _(1-y) light _- receiving layer 2.5 μm or more, the nitrogen composition (y) must be 0.08 or more. However, when the nitrogen composition (y) exceeds 0.02, there is a strong tendency for the crystal quality to deteriorate, and it is possible to ensure good crystallinity while containing nitrogen exceeding 0.02 and reaching about 0.08. very difficult.

  There is a very high demand for light receiving elements having a wide light receiving sensitivity in the longer wavelength region of the near infrared region, and development of a light receiving device having a light receiving sensitivity in the near infrared region using an InP substrate is desired. An object of the present invention is to provide a light receiving element having a small dark current and having a light receiving sensitivity on a longer wavelength side in the near infrared region using an InP substrate.

  The light receiving element of the present invention includes an InP substrate, an InAsP graded buffer layer that is positioned on the InP substrate, and has an (As / P) ratio increased stepwise in a direction away from the InP substrate, and an InAsP graded buffer layer And a GaInNAs light-receiving layer located in the region.

  GaInNAs containing N in high In composition InGaAs (hereinafter referred to as GaInNAs unless otherwise specified) has a smaller lattice constant and a band gap than high In composition InGaAs. Becomes narrower and the absorption edge wavelength becomes longer. Although the lattice constant is reduced by N, since the In composition is high, the lattice constant of GaInNAs is larger than the lattice constant of the InP substrate. When showing the magnitude relationship of the lattice constants, InP <GaInNAs <high In composition InGaAs.

For this reason, as described above, an InAsP graded buffer layer is interposed between the InP substrate and GaInNAs to relax the lattice mismatch, and a GaInNAs light-receiving layer having a good crystallinity can be grown. In addition, even _if the nitrogen composition (y) of the Ga _x In _(1-x) N _y As _(1-y) light _- receiving layer is less than 0.08, the GaInNAs light-receiving is performed while lattice-matching with the base (InAsP graded buffer layer). The absorption edge wavelength of the layer can be increased to 3 μm. Further, since the absorption edge wavelength can be narrowed according to the N composition, the nitrogen composition can be set corresponding to the sensitivity limit on the long wavelength side to be set. For example, even if the nitrogen composition is low, the absorption edge wavelength of the GaInNAs light-receiving layer can be made longer than that of the high In composition GaAs, and the crystallinity can be improved. For this reason, the options (N composition and the number of graded buffer layers) for further reducing the dark current can be diversified.

  As described above, the lattice constant of GaInNAs is larger than InP, but smaller than InGaAs having a high In composition. For this reason, the number of InAsP graded buffer layers interposed between the InP substrate and the light receiving layer is smaller in the case of the GaInNAs light receiving layer in the present invention. In InAsP forming a graded buffer layer, when the (As / P) ratio increases, the lattice constant increases, the band gap narrows, and the absorption edge wavelength becomes longer. As a matter of course, the (As / P) ratio of the InAsP graded buffer layer is low on the InP substrate side and high on the GaInNAs light receiving layer side. As a result, the absorption of near-infrared light on the long wavelength side is reduced in the InAsP graded buffer layer in the light receiving element of the present invention. For this reason, for example, in the case of a back-illuminated light receiving element in which signal light is incident from the back side of the InP substrate, the light receiving element has a near-infrared region compared to a high In composition InGaAs provided with an InAsP graded buffer layer. The light receiving sensitivity on the long wavelength side can be improved.

  An InAsP window layer located on the GaInNAs light-receiving layer can be provided. With this InAsP window layer, the dark current can be lowered.

Additional GaInNAs absorption layer includes at least one of Sb and P, when viewing their status _{Ga x In (1-x)} N y As (1-y-m-n) Sb m P n, the composition m , N or m + n can be 0.0001 or more and 0.02 or less. Thereby, the crystallinity of the GaInNAs light-receiving layer is improved, and the dark current can be further suppressed.

  The InAsP graded buffer layer can be doped with Si. Since Si pinches lattice defects in the crystal, the growth of lattice defects can be suppressed, and the density of lattice defects can be suppressed.

  In addition, Sb may be included in the InAsP graded buffer layer. Since Sb improves the flatness of the InAsP / InAsP interface of the graded buffer layer in the crystal, it suppresses the generation of lattice defects at the interface and is effective in maintaining a low lattice defect density.

  The InAsP window layer described above can be composed of a plurality of InAsP layers in which the (As / P) ratio is gradually reduced in a direction away from the InP substrate. Accordingly, in the case of a top-illuminated type light receiving element in which signal light is incident from the upper surface of the epitaxial layer based on the above-described effect of the As composition of InAsP on the absorption edge wavelength, the absorption of the optical signal in the window layer can be reduced. As a result, it is possible to suppress a decrease in sensitivity in the wavelength region near or below the wavelength of 1.7 μm.

  According to the present invention, it is possible to obtain a light receiving element having a small dark current by using an InP substrate and expanding the light receiving sensitivity toward the long wavelength side in the near infrared region.

(Embodiment 1)
FIG. 1 is a cross-sectional view showing a light receiving element 10 according to Embodiment 1 of the present invention. According to FIG. 1, in the light receiving element 10, a stacked semiconductor layer having the following configuration is grown on the S-doped InP substrate 1.
(S-doped InP substrate 1 / InAsP graded buffer layer 20 / GaInNAs light receiving layer 3 / InAsP window layer 4 / selective diffusion mask 5)
The p-type region 15 located so as to reach from the InAsP window layer 4 to the GaInNAs light-receiving layer 3 is formed by Zn being diffused and introduced from the opening of the selective diffusion mask 5 of the SiN film having a thickness of 100 nm. A p-type electrode 12 made of AuZn is provided in the p-type region 15, and an n-type electrode 11 made of AuGeNi is provided in ohmic contact with the back surface of the InP substrate 1. In the GaInNAs light-receiving layer 3, a pn junction is formed at a position corresponding to the boundary of the p-type region 15, and a depletion layer is formed by applying a reverse bias voltage between the p-part electrode 12 and the n-part electrode 11. Arise. When the signal light is incident from the InAsP window layer 4 side as shown in FIG. 1, the light in the near infrared region excites electrons located in the valence band of the depletion layer of the GaInNAs light receiving layer to the conduction band, A photocurrent is generated between the electrodes.

  When the crystallinity of the GaInNAs light receiving layer 3 is not good, an impurity level or the like is generated, and a thermally excited current, that is, a dark current is generated even when light is not incident. As described above, the GaInNAs light-receiving layer 3 has a high In composition of (number of In atoms / number of Ga atoms) = (0.82 / 0.18). Even if the constant becomes smaller, the lattice constant is still larger than that of the InP substrate. In order to alleviate this difference in lattice constant, the InAsP graded buffer layer 20 is disposed.

  In the above-mentioned Non-Patent Document 1, 12 to 20 graded buffer layers are interposed between the InP substrate and the high In composition InGaAs light receiving layer 3. Although the GaInNAs light-receiving layer 3 in the present embodiment contains N and has a lattice constant smaller than that of the high In composition InGaAs, in order to improve the crystallinity, the step of the lattice constant, that is, the step of the (As / P) ratio is reduced. Therefore, it has 17 layers. The step from the InP substrate 1 can be epitaxially grown or within the lattice matching range. The lattice matching range is a range where | Δa / a | ≦ 0.002, where a is the lattice constant of each layer and Δa is the difference between the lattice constants of the upper and lower graded layers.

The increment of the graded buffer layer in Non-Patent Document 1 is 0.05, whereas the increment of this embodiment is 0.03. That is, in Non-Patent Document 1, the x value of InAs _x P _1-x changes from 0 (zero) → 0.05 → 0.10 → 0.15. On the other hand, in the present embodiment, the x value changes as 0 (zero) → 0.03 → 0.06 → 0.09. In this case, | Δa / a | = 0.016 in Non-Patent Document 1, whereas | Δa / a | = 0.0009 is very small in the embodiment of the present invention, and therefore the level of lattice matching is high. . As a result, the lattice defect density generated at each layer interface of the graded buffer layer 20 and inherited to the upper layer is low in the photodiode 10 in the present embodiment, so that the dark current can be further reduced. .

  In addition, the GaInNAs light-receiving layer 3 containing N has a lattice constant smaller than that of the high InGaAs light-receiving layer, but the band gap energy is reduced as described above. In comparison, it can have light receiving sensitivity up to a longer wavelength range. The wavelength of 2.6 μm of the high InGaAs light receiving layer is the limit of light receiving sensitivity. In addition, even if the N composition is not increased to about 8% but lower than that, the above-described N-specific effects of reduction of the lattice constant and reduction of the band gap energy can be obtained. In view of the above, an appropriate N composition lower than 8% can be selected.

  FIG. 2 is a diagram showing the film thickness, composition, and the like of each layer, the GaInNAs light receiving layer 3 and the InAsP window layer 4 in the InAsP graded buffer layer 20 of FIG. The InP substrate 1 is preferably an S-doped 2-inch substrate having a plane orientation of (100) ± 3 °. As the film-forming method for epitaxial growth on the InP substrate 1, it is preferable to use the MBE (Molecular Beam Epitaxy) method for forming the GaInNAs light-receiving layer 3 in terms of reducing the hydrogen concentration. The InAsP graded buffer layer 20 and the InAsP window layer 4 may be formed by MBE, OMVPE (Organometallic Vapor Phase Deposition), or chloride VPE.

  In the growth of the GaInNAs light-receiving layer 3, N is contained in an N composition (y) of 0.02 so that the absorption edge wavelength λcut-off is, for example, 2.9 μm, that is, about 2 at% in the group V atom. Since the lattice constant changes according to the N composition, the number of InAsP graded buffer layers 20 is changed to an appropriate one according to the N composition. At this time, as described above, the increment from the InP substrate 1 is epitaxially grown or within the lattice matching range.

As shown in FIG. 2, the epitaxially grown layer immediately above the InP substrate 1 is InAs _0.03 P _0.97 , and the As composition step is 0.03. Since InAs _0.51 P _0.49 is in the lattice matching range with respect to GaInNAs having the N composition, graded so that the uppermost layer of InAsP graded buffer layer 20 is InAs _0.51 P _0.49. Set the number of layers. In the case of FIG. 2, there are 17 layers. Although the difference in lattice constant between the InP substrate and the light-receiving layer is smaller than that shown in Non-Patent Document 1, by taking a sufficient number of layers in this way, the lattice defect density can be reduced and darkness is reduced. A reduction in current can be realized.

  Up to the InAsP window layer 4, epitaxial growth is performed by the above-described film forming method to form a semiconductor multilayer structure. Thereafter, as described above, Zn as a p-type impurity is introduced from the opening of the mask pattern 5 of the SiN film so as to reach the GaInNAs light-receiving layer 3 to form a pn junction or a p-type region 15. Further, a p-electrode 12 of AuZn and an n-electrode 11 of AuZeNi are provided.

(Modification (1) of Embodiment 1)
FIG. 3 is a diagram showing a semiconductor stacked structure in a modification (1) of the first embodiment of the present invention. The modification (1) of the first embodiment is characterized in that the InAsP graded buffer layer 20 is doped with Si. The Si doping concentration is 2 × 10 ¹⁷ / cm ³ . However, a non-doped InAsP buffer layer 9 having a thickness of 1 μm is provided immediately below the GaInNAs light-receiving layer 3.

When the InAsP graded buffer layer 20 is doped with Si, lattice defects are pinned by Si, and the lattice defect density can be reduced without causing growth of lattice defects. For this purpose, the InAsP graded buffer layer 20 is doped with Si. However, in order to form a pin photodiode immediately below the GaInNAs light-receiving layer 3, Si of about 10 ¹⁷ / cm ³ or less is doped or non-doped. As shown in FIG. 3, by doping Si into the InAsP graded buffer layer 20, the lattice defect density of each layer of the InAsP graded buffer layer 20 is reduced, and the lattice defect density inherited and accumulated as the layers are stacked is changed to the uppermost layer. Can be greatly reduced. As a result, the lattice defect density of the non-doped InAsP buffer layer 9 and the GaInNAs light receiving layer 3 can be reduced, and the dark current can be significantly suppressed.

(Modification (2) of Embodiment 1)
FIG. 4 is a diagram showing a semiconductor laminated structure in a modification (2) of the first embodiment of the present invention. The modification (2) of the first embodiment is characterized in that Sb is added to the InAsP graded buffer layer 20. The amount of Sb added is 0.1 at% or more and 1 at% or less in the group V atom. That is, InAs _x P _(1−x−m) Sb _m ((0.001 ≦ m ≦ 0.01). Since Sb does not affect the carrier density or the carrier conductivity type, it is directly under the GaInNAs light receiving layer 3. Sb is also added to the InAsP buffer top layer 9 having a thickness of 1 μm provided in Fig. 4. In Fig. 4, Sb-added InAs (0.03) P (0.97) is indicated, but this means that In the growth operation, this means that Sb is added while growing the InAsP film with the target of (As / P) = (0.03 / 0.97), and the composition of the InAsP film obtained as a result of the growth is as follows. Since Sb is a group V element, it is substituted with As or P and slightly deviates from the group V composition shown in Fig. 4. When the Sb composition is InAs _0.03-x P _0.97-y Sb _{x + y} , x + y = About 0.005 .

  Sb improves the flatness of the interface of each layer of the InAsP graded buffer layer 20. Therefore, generation of lattice defects starting from the interface can be suppressed. Therefore, the uppermost layer of the Sb-added InAsP graded buffer layer 20 or the Sb-added InAsP buffer layer 9 does not accumulate the inheritance from lattice defects at each interface origin, and as a result, the lattice defect density in these uppermost layers is suppressed. And ultimately the dark current can be reduced.

(Modification (3) of Embodiment 1)
FIG. 5 is a diagram showing a semiconductor stacked structure in a modification (3) of the first embodiment of the present invention. The modification (3) of the first embodiment is characterized in that the light receiving layer 3 is made of GaInNAsSb instead of GaInNAs. GaInNAsSb tends to obtain better crystallinity than GaInNAs. For this reason, a favorable crystalline GaInNAsSb light-receiving layer can be obtained and dark current can be suppressed. As described above, the crystallinity can be improved by adding P to GaInNAs in the same manner as Sb is added to GaInNAs to improve the crystallinity. Therefore, GaInNAsP may be used for the light receiving layer.

(Embodiment 2)
FIG. 6 is a diagram illustrating the photodiode 10 according to the second embodiment of the present invention. This embodiment is characterized in that it is epi-down mounted. In the case of epi-down mounting, since light enters from the back surface of the InP substrate 1, the n-part electrode 11 is preferably provided in a ring shape on the InAsP graded buffer layer 20. The InAsP graded buffer layer 20 is preferably doped with an n-type impurity such as Si. In addition, an Fe-doped semi-insulating InP substrate 1 is preferably used as the InP substrate, and a protective film 37 is preferably provided on the Fe-doped semi-insulating InP substrate 1 in order to limit an opening through which light is incident. The Fe-doped semi-insulating InP substrate has no free electron absorption compared to the S-doped InP substrate, and the attenuation of the signal light is slight. For this reason, in a back-illuminated type light receiving element (see FIG. 6) that passes through the InP substrate 1 before being received, the Fe-doped semi-insulating InP substrate in which the attenuation of the signal light is small can achieve higher sensitivity. . 2 to 5 can be used for the semiconductor laminated structure. In that case, the layer where the n-part electrode 11 of the InAsP graded buffer layer 20 is arranged has n-type impurities such as those described above. It is preferable to dope Si having a pinning action such as dislocation in order to realize ohmic contact and to prevent the growth of lattice defects.

  6, the As composition or (As / P) ratio of the InAsP graded buffer layer 20 is relatively low compared to the InAsP graded buffer layer in Non-Patent Document 1. It stops at. For this reason, the longest wavelength of the absorption edge wavelength of the InAsP graded buffer layer 20 is correspondingly smaller than that of the InAsP graded buffer layer in Non-Patent Document 1. As a result, the InAsP graded buffer layer 20 of the light receiving element 10 shown in FIG. 6 has no absorption on the longer wavelength side than the predetermined wavelength, and as a result, a near-infrared long wavelength region targeted by the light receiving element of the present invention. The sensitivity at can be increased. That is, not only can the crystallinity of the light receiving layer be improved by reducing the number of graded buffer layers, but also the sensitivity in the long wavelength region of the near infrared region, which is important in the present invention when epi-down mounting is performed. Can do. In order to reduce the above absorption, the thickness of each graded buffer layer 20 is preferably reduced to about 20 nm.

(Embodiment 3)
FIG. 7 is a diagram showing the photodiode 10 according to the third embodiment of the present invention. As shown in FIG. 8, the feature of the present embodiment is that the window layer is a graded InAsP layer in which the As composition is decreased stepwise in the direction away from the light receiving layer 3. In the graded InAsP window layer 40, the InAs _0.03 P _0.97 layer is formed by gradually reducing the As composition or (As / P) ratio from InAs _0.51 P _0.49 epitaxially grown on the GaInNAs light-receiving layer 3. Then, a laminated structure of each epitaxial growth layer reaching the uppermost InP layer is taken. In the graded InAsP window layer 40, the uppermost InP layer is 300 nm, but the layers below it are made as thin as 20 nm. Other portions are the same as those of the photodiode 10 shown in FIG.

According to the graded InAsP window layer 40 described above, the thickness of InAsP having a high As composition ((As / P) ratio) is reduced. In particular, the thickness of the InAs _0.51 P _0.49 layer is 20 nm (0. 02 μm) and thin. For this reason, the absorption of light in the vicinity of the wavelength of 1.7 μm or longer than that is reduced, and the sensitivity in the long wavelength region of the near infrared, which is important in the light receiving element targeted by the present invention, is shown in FIGS. It can be higher than each light receiving element shown. In the light receiving element shown in FIGS. 1 to 6, since the window layer is made of InAs _0.51 P _0.49 having a thickness of 0.5 μm, absorption of light in the vicinity of a wavelength of 1.7 μm or a longer wavelength region is large.

(Modification (1) of Embodiment 3)
FIG. 9 is a diagram showing a semiconductor stacked structure in a modification (1) of the third embodiment of the present invention. The modification (1) of the third embodiment is characterized in that Sb is added to the InAsP graded window layer 40. Regarding the display of the composition of As and P of the group V element in the figure, the description in the modification (2) of the first embodiment is applicable as it is. Sb may or may not be added to the uppermost InP window layer.

  As described above, Sb improves the flatness of the interface of each layer of the InAsP graded window layer 40. Therefore, generation of lattice defects starting from the interface can be suppressed. For this reason, the inheritance from the lattice defect of each interface origin is not accumulated in the uppermost layer of the Sb-added InAsP graded window layer 40 or the InP layer 9. As a result, the lattice defect density in these uppermost layers can be suppressed. As a result, it is possible to improve sensitivity by reducing light scattering and the like.

  In the above embodiment, the light receiving element having a single light receiving layer has been described. However, the light receiving element of the present invention includes a two-dimensionally arranged imaging device, such as a sensor in which the light receiving layer is one-dimensionally or two-dimensionally arranged. Needless to say. Further, the factor for improving the dark current, for example, Si doping or Sb addition to the InAsP graded buffer layer is not limited to a single one, and includes a combination thereof.

  Although the embodiments and examples of the present invention have been described above, the embodiments and examples of the present invention disclosed above are merely examples, and the scope of the present invention is the implementation of these inventions. It is not limited to the form. The scope of the present invention is indicated by the description of the scope of claims, and further includes meanings equivalent to the description of the scope of claims and all modifications within the scope.

  According to the present invention, it is possible to obtain a light receiving element that uses an InP substrate and expands sensitivity to a long wavelength region in the near infrared region and suppresses dark current.

It is sectional drawing which shows the light receiving element (photodiode) in Embodiment 1 of this invention. It is sectional drawing which shows the semiconductor laminated structure of the light receiving element of FIG. It is sectional drawing which shows the semiconductor laminated structure of the light receiving element in the modification (1) of Embodiment 1 of this invention. It is sectional drawing which shows the semiconductor laminated structure of the light receiving element in the modification (2) of Embodiment 1 of this invention. It is sectional drawing which shows the semiconductor laminated structure of the light receiving element in the modification (3) of Embodiment 1 of this invention. It is sectional drawing which shows the light receiving element (photodiode) in Embodiment 2 of this invention. It is sectional drawing which shows the light receiving element (photodiode) in Embodiment 3 of this invention. It is sectional drawing which shows the semiconductor laminated structure of the light receiving element of FIG. It is sectional drawing which shows the semiconductor laminated structure of the light receiving element in the modification (1) of Embodiment 3 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 InP board | substrate, 3 N containing InGaAs type light receiving layer, 4 InAsP window layer (single layer), 5 diffusion mask pattern, 9 Sb addition InAsP buffer top layer, 10 light receiving element (photodiode), 11 n part electrode, 12 p part Electrode, 15 p-type region, 20 InAsP graded buffer layer, 37 protective film, 40 InAsP graded window layer.

Claims (6)

An InP substrate;
An InAsP graded buffer layer positioned on the InP substrate and gradually increasing the (As / P) ratio in a direction away from the InP substrate;
A light receiving element comprising: a GaInNAs light receiving layer located on the InAsP graded buffer layer.   The light receiving element according to claim 1, further comprising an InAsP window layer positioned on the GaInNAs light receiving layer. Wherein the GaInNAs absorption layer, at least one of Sb and P are included, when displaying the state _{Ga x In (1-x)} N y As (1-y-m-n) Sb m P n, the composition m , N, or m + n is 0.0001 or more and 0.02 or less, and the light receiving element according to claim 1 or 2.   The light receiving element according to claim 1, wherein the InAsP graded buffer layer is doped with Si.   The light receiving element according to claim 1, wherein Sb is contained in the InAsP graded buffer layer. 6. The light receiving element according to claim 1, wherein the InAsP window layer includes a plurality of InAsP layers whose (As / P) ratio is gradually reduced in a direction away from the InP substrate. .

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