JP2014192488A - Semiconductor light-receiving element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor light-receiving element capable of operating in a wavelength region of about 2 μm on an InP substrate without providing a buffer layer of an advanced InGaAs light-receiving element for changing a grating constant.SOLUTION: A semiconductor light-receiving element 100 comprises an InP substrate 101, an InGaAsSb light absorbing layer 105 formed on the InP substrate 101 and having a compressive strain structure, and reflecting mirrors 102 and 107 for forming a resonator. The reflecting mirror 102 is formed between the InP substrate 101 and the InGaAsSb light absorbing layer 105 and has a multilayer structure.

Description

  The present invention relates to a semiconductor light receiving element, and more particularly to a semiconductor light receiving element that operates in a wavelength region near 2 μm.

  In recent years, in order to protect the environment, it has become increasingly important to reduce the environmental load generated by humans, for example, by reducing the amount of gas emitted from factories, power plants, garbage incineration facilities, automobiles, and the like. In order to reduce the amount of gas emission, it is necessary to measure the gas emission source and the gas concentration in the atmosphere with high accuracy. Gas measurement using light absorption by a gas absorption line is characterized in that it can be measured in real time, remotely, and even gas isotopes can be specified, and is applied to various gas measurement systems.

FIG. 7 is a diagram showing gas types having absorption lines in the wavelength region near 2 μm and their intensities. In this wavelength range, not only gas species such as CO ₂ , CH ₄ , and N ₂ O, which have a great impact on the global greenhouse effect, but also emission standards from factories and incineration facilities are established to control air pollution. There are absorption lines of gas species such as HCl, NH ₃ , and CO. For this reason, it is one of the important wavelength regions in gas measurement.

In FIG. 7, for each gas type, a wavelength region having a large absorption line intensity is surrounded by a thick line, and a range surrounded by the thick line includes a plurality of isolated absorption lines. As an example of this, FIG. 8 shows an absorption line in a wavelength region near 2.05 μm of CO ₂ . In FIG. 8, nine strong absorption lines exist in a wavelength region of only 5 nm. It can be seen that these individual absorption lines have a sharp spectral shape with a peak half-value width of 0.1 nm or less.

  In general, in gas measurement using a gas absorption line, one absorption line is employed among a plurality of absorption lines as shown in FIG. 8 as an example, and a change in the amount of light absorption by the one absorption line is employed. It is known to perform concentration measurement.

  On the other hand, in order to measure the change in the amount of light absorption, a light source (single wavelength light source) and a light receiving element are required. For example, when gas measurement is performed using a single absorption line as described in the example of FIG. 8, the operating wavelength range between the light source and the light receiving element may be narrow. There are many cases.

  Thus, the wavelength region in the vicinity of 2 μm is an important region in gas measurement using light absorption by gas absorption lines. For this reason, the light source and the light receiving element operating in this wavelength region are required to have high performance.

  For light sources operating in the wavelength region near 2 μm, a semiconductor laser having an active layer with a multiple quantum well structure including an InGaAs strained quantum well layer on an InP substrate has been put into practical use, and this semiconductor laser matches the wavelength of the gas species. The laser can be manufactured.

  On the other hand, in general, a photoconductive light-receiving element having a light absorption layer of PbS operating in a wide wavelength region of 1 to 2.9 μm has been used in the past. However, since the photoconductive light receiving element has a problem that the response speed is slow, in recent years, a photovoltaic light receiving element having a high response speed called an extended InGaAs light receiving element has been used.

  FIG. 9 is a diagram schematically showing a layer structure of a general extended type InGaAs light receiving element 900. In FIG. 9, the layer structure of the extended InGaAs light receiving element 900 includes an InAsP buffer layer 902 in which the As composition is increased stepwise on an n-type InP substrate 901, an InGaAs light absorption layer 903, and an InAsP window layer 904. Consists of.

  The InGaAs lattice constant matches the InP lattice constant, and the In composition ratio is 0.53. In this case, the band gap wavelength is 1.67 μm. For this reason, it is difficult to detect light having a wavelength of 1.7 μm or more in a light receiving element using InGaAs lattice-matched to InP as a light absorption layer.

  Here, in order to be able to detect light having a wavelength of 1.7 μm or more by the InGaAs light absorption layer 903, it is necessary to increase the In composition ratio. However, when an InGaAs light absorption layer 903 having a large In composition ratio and a large film thickness is directly grown on an InP substrate 901, misfit dislocations due to lattice mismatch (indicated by bold lines in FIG. 9). ) Due to a large number of crystal defects, and the light receiving sensitivity of the light receiving element decreases.

  Therefore, the extended InGaAs light-receiving element 900 employs an InAsP buffer layer 902 in which the As composition is increased stepwise in order to suppress the occurrence of misfit dislocations in the InGaAs light absorption layer 903, and moves away from the InP substrate 901. The lattice constant of the InAsP buffer layer 902 is increased. The InGaAs light absorption layer 903 having a relatively large In composition ratio is substantially lattice-matched with the uppermost layer of the InAsP buffer layer. That is, the extended InGaAs light receiving element 900 is configured so that misfit dislocations due to lattice mismatch between the InGaAs light absorption layer 903 and the InAsP buffer layer 902 are less likely to occur.

  At present, an extended InGaAs light-receiving element having an In composition ratio of the InGaAs light absorption layer of about 0.8 is also commercially available, and can cope with a wavelength region near 2.5 μm.

  As described above, the extended InGaAs light receiving element 900 uses the InAsP buffer layer 902 whose As composition is increased stepwise, increases its lattice constant, and uses the InGaAs light absorption layer 903 as a lattice matching condition as the uppermost layer. It is produced by crystal growth in a close state. In this case, an increase in lattice constant in the InAsP buffer layer 902 is realized by causing lattice relaxation in the InAsP buffer layer 902. In this case, misfit dislocations due to lattice mismatch occur in the InAsP buffer layer 902, but the dislocations are prevented from propagating to the InGaAs absorption layer by devising the layer configuration and manufacturing method. Non-patent document 1 discloses a conventional InGaAs optical device.

K. Makita et al., “Ga1-yInyAs / InAsxP1-x (y> 0.53, x> 0) pin photodiodes for long wavelength regions (・> 2 ・ m) grown by hydride vapor phase epiytaxy,” Electronics Letters, Vol. 24, No. 7, 1988, 379-380.

  In general, in gas measurement using light absorption by a gas absorption line in a wavelength region near 2 μm, an extended InGaAs light receiving element is used as the light receiver. As shown in FIG. 9, this extended type InGaAs light receiving element has a layer structure on the premise that misfit dislocations due to lattice mismatch are generated in the InAsP buffer layer and the lattice constant is increased in the InAsP layer. ing. However, it is difficult to completely suppress the propagation of dislocations generated in the InAsP buffer layer to the InGaAs absorption layer. As a result, crystal defects also occur in the InGaAs absorption layer. In the light receiving element disclosed in Non-Patent Document 1, dark current increases due to crystal defects in the InGaAs absorption layer. For this reason, it is difficult to reduce the dark current in the extended type InGaAs light receiving element.

  The present invention has been made in view of the above situation, and operates in a wavelength region near 2 μm on an InP substrate without providing a buffer layer for changing a lattice constant unlike an extended InGaAs light receiving element. An object of the present invention is to provide a possible semiconductor light receiving element.

  The present invention for solving the above problems is a semiconductor light receiving element for converting an optical signal into an electric signal, an InP substrate, an InGaAsSb light absorption layer formed on the InP substrate and having a compressive strain structure, and a resonance A first reflecting mirror and a second reflecting mirror for forming a container, wherein the first reflecting mirror is formed between the InP substrate and the InGaAsSb light absorbing layer and has a multilayer structure.

  Here, when the Sb composition ratio of the InGaAsSb light absorption layer is x, x is in the range of 0 <x ≦ 0.3, and the lattice constant of the InGaAsSb light absorption layer is larger than the lattice constant of InP, If the lattice mismatch ratio of InGaAsSb light absorption layer to InP is P, P may be in the range of 0% <P ≦ 1.5%.

  The multilayer structure of the first reflecting mirror may include two or more elements of In, Ga, Al, As, and P as constituent elements, and may be configured to lattice match with InP.

  According to the conductor light receiving element of the present invention, it is possible to operate on the InP substrate in a wavelength region near 2 μm without providing a buffer layer for changing the lattice constant unlike the extended InGaAs light receiving element.

It is a figure which shows the structural example of the semiconductor light receiving element in Embodiment 1 of this invention. It is a figure for demonstrating an example of a change of the band gap wavelength of InGaAsSb at the time of changing Sb composition ratio. It is a figure for demonstrating the change of the band gap wavelength when changing Sb composition ratio about InGaAsSb on an InP board | substrate considering the shift of the band edge by a lattice distortion. It is a figure for demonstrating in relation to the ratio of the lattice mismatch with respect to InP, an example of the film thickness in which a lattice relaxation arises when the lattice mismatch with respect to InP is changed about InGaAs on an Inp substrate. FIG. 5 is a characteristic diagram for explaining an example of a change in photoluminescence spectrum at room temperature when the growth film thickness is changed for InGaAsSb having a lattice mismatch of + 0.4% with respect to InP grown on an InP substrate. . It is a figure which shows the structural example of the semiconductor light receiving element in Embodiment 2 of this invention. It is a figure for demonstrating in association with the intensity | strength the gas seed | species with which an absorption line exists in the wavelength range of 2 micrometers. Wavelength of CO ₂ is a diagram for explaining the absorption line near 2.05. It is sectional drawing for demonstrating the layer structure of a general expansion type InGaAs light receiving element.

<First Embodiment>
The first embodiment of the semiconductor light receiving element of the present invention will be described below. The semiconductor light receiving element of this embodiment is configured to convert an optical signal into an electrical signal.

[Configuration of semiconductor light receiving element]
First, a configuration example of the semiconductor light receiving element 100 of the present embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration example of the semiconductor light receiving element 100 according to the first embodiment of the present invention.

  The semiconductor light receiving element 100 includes an n-type InP substrate 101, a reflecting mirror (first reflecting mirror) 102 formed on the n-type InP substrate 101, an n-type InGaAsP layer 103 formed on the reflecting mirror 102, and The undoped InGaAsP layer 104 formed on the n-type InGaAsP layer 103, the undoped InGaAsSb light absorption layer 105 formed on the InGaAsP layer 104, and the p-type InGaAsP layer 106 formed on the InGaAsSb light absorption layer 105 And a p-type InGaAs layer 107 formed on the p-type InGaAsP layer 106.

  In FIG. 1, the band gap wavelengths of the n-type InGaAsP layer 103, the InGaAsP layer 104, and the p-type InGaAsP layer 106 are all 1.5 μm, for example.

  InGaAsSb layer 105 has, for example, Sb composition ratio = 0.04, In composition ratio = 0.55, lattice mismatch with InP = + 0.4%, band gap wavelength = 1.83 μm, and film thickness = 0.35 μm. Given in. Note that the values shown in the description of this embodiment are merely examples, and may be changed as appropriate.

  The reflecting mirror 102 has a semiconductor multilayer structure. In this multilayer structure, for example, an n-type InGaAsP layer having a band gap wavelength of 1.5 μm and a film thickness of 130 nm and an n-type InP layer having a band gap wavelength of 1.5 μm and a film thickness of 141 nm are formed as one pair. For example, 10 pairs are stacked in the reflecting mirror 102. In this case, the reflecting mirror 102 has a reflectance of 81% with respect to light having a wavelength of 1.78 μm, for example. The wavelength of 1.78 μm corresponds to the wavelength at which the HCl gas absorption line exists as shown in FIG.

  The p-type InGaAs layer 107 functions as a reflecting mirror (second reflecting mirror) that reflects signal light at the boundary with air. The reflectance in this embodiment is 30%, for example.

  In FIG. 1, the silicon nitride film 108, the p-type electrode 109, and the n-type electrode 110 other than the constituent elements 101 to 107 are referred to in the description of the manufacturing method described later.

[Method for Fabricating Semiconductor Light-Receiving Element]
Next, a method for manufacturing the semiconductor light receiving element 100 of the present embodiment will be described with reference to FIG. 1 again.

For the growth of the epitaxial wafer, for example, a metal organic molecular beam epitaxy method is used. As raw materials in this case, for example, triethylgallium (TEGa) and trimethylindium (TMIn) as group III raw materials, arsine (AsH ₃ ), phosphine (PH ₃ ) and trisdimethylaminoantimony (TDMASb) as group V raw materials, dopant raw materials Tin (Sn) and beryllium (Be) are used. The substrate temperature during crystal growth is, for example, 500 ° C. in all layers.

  In FIG. 1, in the layers other than the InGaAsSb light absorption layer 105, the raw material supply amount is adjusted so that the lattice constant difference with respect to InP is less than 0.1%.

  After forming a circular mesa (see FIG. 1) having a diameter of, for example, 1130 μm using the above-described epitaxial wafer, a nitrogen silicon film 108 is deposited.

  After removing the nitrogen silicon film 108 at the center of the mesa portion, for example, a ring-shaped p-type electrode 109 having an outer diameter = 1100 mm and an inner diameter = 1000 mm is formed.

  Finally, the InP substrate 110 is adjusted to a predetermined thickness by polishing, and then the n-type electrode 110 is formed.

  Here, in the semiconductor light receiving element 100 of the present embodiment, for example, when the operating temperature = 20 ° C. and the bias voltage = −5V, the peak wavelength of the photocurrent is 1.78 μm. The quantum efficiency at the peak wavelength is 62%, but these characteristics are better than those of the semiconductor light receiving element that does not include the reflecting mirror 102 (including the constituent elements 101 and 103 to 110 other than the reflecting mirror 102). .

  In the case of a semiconductor light receiving element that does not include the reflecting mirror 102, for example, the quantum efficiency when a peak wavelength of photocurrent = 1.75 μm is given is 21%, and the quantum efficiency when a wavelength = 1.78 μm is given is 20%. That is, in the semiconductor light receiving element 100, the quantum efficiency is improved about three times as compared with the case where the reflecting mirror 102 is not provided. This is because the region including the InGaAsSb absorption layer 105 functions as a resonator between the surface of the reflecting mirror 102 and the reflecting mirror surface of the p-type doped InGaAs layer 107 (interface with air).

  In the semiconductor light receiving element 100, for example, the quantum efficiency is 31% or more, which is half the peak value, when the wavelength region is from 1.72 μm to 1.82 μm.

  In general, it is known that each absorption line of gas has a sharp spectral shape with a peak half-value width of 0.1 nm or less as described with reference to FIGS. 7 and 8. It is known that one absorption line among the lines is used as a measurement object.

  From this viewpoint, the semiconductor light receiving element 100 of the present embodiment having a narrow operating wavelength and high quantum efficiency is suitable for application to gas measurement using light absorption by a gas absorption line.

In the semiconductor light receiving element 100, when the operating temperature is 20 ° C. and the bias voltage is −0.5 V, the dark current is 0.11 ± 0.03 μA (14 ± 4 μA / cm ² ). That is, it is lower than a general extended type InGaAs light receiving element (for example, KR Linga et al., “Dark current analysis and characterization of InxGa1-xAs / InAsyP1-y graded photodiodes with x> 0.53 for response to longer wavelengths (> 1.7 μm), “IEEE Journal of Lightwave Technology,” Vol. 10, No. 8, 1992, 1050-1055). As will be described later, the InGaAsSb light absorption layer 105 is lattice mismatched with the InP substrate 101. This is because the thickness of the InGaAsSb light absorption layer 105 is small and crystal defects due to misfit dislocations are reduced.

  Here, in the semiconductor light receiving element 100, the thickness of the InGaAsSb light absorption layer 105 is, for example, 0.35 μm, which is thinner than the light absorption layer of the general light receiving element shown in FIG. .

  In the semiconductor light receiving element 100 of the present embodiment, the reflecting mirror 102 is provided so that the light receiving sensitivity is increased even if the light absorption layer 105 is thinned. Such a light receiving element is generally called a Resonant Cavity Enhanced (RCE) Photodetector (for example, K. Kishino et al., “Resonant cavity-enhanced (RCE) detectors,” IEEE Journal of Quantum Electronics, Vol. 27 , No. 8, 1991, 2025-2034). With the configuration of the reflecting mirror 102, it is possible to selectively increase only the light receiving sensitivity in the wavelength region where the reflectance is high.

  In addition, although the case where the reflecting mirror 102 shown in FIG. 1 is formed with a multilayer structure including an InP layer and an InGaAsP layer is illustrated, two or more elements of In, Ga, Al, As, and P are illustrated. As a constituent element, and a semiconductor material that can be doped with a material that can be lattice-matched to the InP substrate 101, the present invention is not limited thereto. Examples of the multilayer structure of the reflecting mirror 102 include a multilayer film composed of InP and InGaAs, a multilayer film composed of InGaAs and InAlAs, and a multilayer film composed of InGaAs and InP. Even if it does in this way, if the film thickness of the reflective mirror 102 is adjusted, it is clear that the same effect as the semiconductor light receiving element 10 of this Embodiment is acquired.

  In the semiconductor light receiving element 100 of the present embodiment, an InGaAsSb layer that does not lattice match with InP is used as the light absorption layer 105, and the band gap wavelength of the InGaAsSb light absorption layer 105 is longer than that of the InGaAs layer that lattice matches. There is a feature in that.

  Next, the band gap wavelength of the InGaAsSb light absorption layer 105 will be described with reference to FIG. FIG. 2 is a diagram for explaining an example of a change in the band gap wavelength of the InGaAsSb light absorption layer 105 when the Sb composition ratio is changed.

  As shown in FIG. 2, the lattice mismatch of InGaAsSb with respect to InP is given values of 0%, + 0.2%, + 0.5%, + 1.0%, and + 1.5%. In this case, the band gap wavelength when InGaAsSb is completely lattice-relaxed takes a value as shown in FIG. When the Sb composition ratio is 0, the band gap wavelength of InGaAs is obtained.

  As shown in FIG. 2, the band gap wavelength of InGaAsSb is such that the Sb composition ratio is within the range of 0 to 0.3 when the Sb composition ratio is in the range of 0 to + 1.5% with respect to InP. It turns out that it becomes a long wavelength with an increase in. That is, in both InGaAsSb and InGaAs, when the lattice mismatch with InP is equal, InGaAsSb has a longer bandgap wavelength than InGaAs when the composition ratio x of InGaAsSb is in the range of 0 <x ≦ 0.3. . In other words, when InGaAsSb is used instead of InGaAs, the bandgap wavelength can be easily increased.

  Here, in the semiconductor light receiving element 100 of the present embodiment, when InGaAsSb is grown on the InP substrate 101, the InGaAsSb crystal lattice is deformed due to the influence of the InP substrate 101. The band edge shift between the conduction band due to valence band and the valence band occurs. An example of the change in the band gap wavelength in this case will be described with reference to FIG.

  FIG. 3 is a diagram for explaining the change of the band gap wavelength when the Sb composition ratio is changed in the InGaAsSb light absorption layer 105 on the InP substrate 101 in consideration of the band edge shift due to the lattice distortion.

  As shown in FIG. 3, the lattice mismatch of InGaAsSb with respect to InP is given values of 0%, + 0.2%, + 0.5%, + 1.0%, and + 1.5%. In this case, the band gap wavelength when InGaAsSb is not completely lattice-relaxed takes a value as shown in FIG. The band gap wavelength shown in FIG. 3 is shorter than the case where the lattice distortion shown in FIG. 2 is not considered because the band edge is shifted by the lattice distortion. However, even when the band edge shift due to the lattice distortion is taken into consideration, the lattice mismatch with respect to InP is 0 to + 1.5% as in the case of FIG. 2 illustrating the value without considering the influence of the lattice distortion. In any range, when the Sb composition ratio is in the range of 0 to 0.3, it can be seen that the wavelength increases with an increase in the Sb composition ratio. That is, even if there is a band edge shift due to lattice distortion as in the InGaAsSb light absorption layer 105 grown on the InP substrate 101, if the composition ratio x of InGaAsSb is in the range of 0 <x ≦ 0.3, InGaAs By adopting InGaAsSb as the light absorption layer instead, the band gap wavelength can be easily increased.

  For example, when the thickness of the InGaAsSb light absorption layer 105 formed on the InP substrate 101 is thin, lattice relaxation does not occur. Therefore, the band gap wavelength of the InGaAsSb light absorption layer 105 is, for example, as shown in FIG. Close to the correct value.

  On the other hand, when the thickness of the InGaAsSb light absorption layer 105 is sufficiently large, the lattice is completely relaxed due to misfit dislocation, so that it is close to the value of the band gap wavelength shown in FIG. 2, for example.

  In the InGaAsSb light absorption layer 105 of the present embodiment, a band gap wavelength located between the value shown in FIG. 2 and the value shown in FIG. 3 is taken according to the lattice relaxation rate described above.

  In general, the above-described film thickness at which lattice relaxation can occur is called a critical film thickness. There is no report on the critical thickness of InGaAsSb, but there are many reports on the critical thickness of InGaAs.

  In the semiconductor light receiving element 100 of the present embodiment, if the Sb composition ratio of the InGaAsSb light absorption layer 105 is 0.3 or less, the composition of InGaAsSb approximates that of InGaAs, and the InGaAsSb light absorption layer 105 is substantially the same as InGaAs. It is considered to have characteristics. This point will be described below.

  FIG. 4 illustrates an example of the critical film thickness at which lattice relaxation occurs when the lattice mismatch with respect to InP is changed in the InGaAsSb light absorption layer 105 on the InP substrate 101 in relation to the ratio of the lattice mismatch with respect to InP. FIG.

  The critical film thickness values shown in FIG. 4 are generally known for the thickness of InGaAs on InP (for example, M. Gendry et al., “Critical thicknesses of highly strained InGaAs layers on InP by molecular beam epitaxy,” Applied Physics Letters, Vol. 60, No. 18, 1992, 2249-2251).

  From FIG. 4, when the lattice mismatch with respect to InP is between 0 and + 1.5%, the critical film thickness is relatively large because the crystal growth proceeds two-dimensionally. On the other hand, when the lattice mismatch becomes larger than + 1.5%, the critical film thickness rapidly decreases because the crystal growth proceeds three-dimensionally. Therefore, when the ratio P of lattice mismatch to InP is greater than 0% and not more than + 1.5% (0 <P ≦ 1.5), the introduction of crystal defects due to the lattice mismatch becomes slow. . This will be described with reference to FIG. 5 using a photoluminescence measurement result of lattice-mismatched InGaAsSb grown on the InP substrate 101.

  FIG. 5 illustrates an example of changes in the photoluminescence spectrum at room temperature when the growth film thickness is changed for InGaAsSb having a lattice mismatch of + 0.4% with respect to InP grown on the InP substrate 101. FIG. The sample was prepared according to the aforementioned organometallic molecular beam epitaxy method. At the time of fabrication, the amount of raw material supplied during InGaAsSb growth was constant for each sample.

  As can be seen from FIG. 5, when the thickness of InGaAsSb is increased from 0.22 μm to 0.35 μm, for example, the emission peak wavelength of photoluminescence changes from 1.80 μm to 1.84 μm, and the peak intensity is 70%. To a degree. The longer emission peak wavelength with this increase in film thickness is because the relaxation of the lattice occurs due to the increase in the film thickness of InGaAsSb, and the shift of the band edge due to the lattice distortion is suppressed.

  The decrease in emission peak intensity is due to the occurrence of crystal defects due to lattice relaxation, but the intensity decrease is only about 30% reduction.

  And even if the film thickness of InGaAsSb increases from 0.35 μm to 0.42 μm, the emission peak wavelength remains at 1.84 μm, and the peak intensity becomes almost constant. As described with reference to FIG. 4, when the ratio P of lattice mismatch to InP is relatively small, 0% <P ≦ + 1.5% or less, the introduction of crystal defects due to lattice mismatch is gradual. It is shown that.

  As described above, according to the semiconductor light receiving element 100 of the present embodiment, InGaAsSb having a lattice constant larger than that of InP is used for the light absorption layer on the InP substrate 101, so that conventionally used InGaAs is used as the light absorption layer. The operating wavelength can be made longer than that of the light receiving element. The InGaAsSb light absorption layer 105 needs to be thin enough that the influence of crystal defects due to misfit dislocations on the device characteristics is not significant. However, the signal light incident on the light receiving element 100 is separated from the InGaAsSb light absorption layer 105 and the InP. Multiple reflection is performed between the reflecting mirror 102 provided between the substrates 101 and the reflecting mirror 107 installed on the signal light incident side. For this reason, even if the thickness of the InGaAsSb light absorption layer 105 is small, a large light receiving sensitivity can be obtained. This eliminates the need for a layer (see FIG. 9) for causing lattice relaxation like the InAsP buffer layer in the above-described extended InGaAs light-receiving element, and allows high sensitivity to signal light having a wavelength of about 2 μm on the InP substrate 101. Can be detected.

  Even if an InGaAsSb layer that is not lattice-matched with InP is used as the light absorption layer 105, if the ratio of lattice mismatch to InP is greater than 0% and less than + 1.5%, crystal defects caused by lattice mismatch Is not introduced rapidly, and as a result, the dark current can be kept small.

  In the present embodiment, the semiconductor light receiving element 100 using InGaAsSb having a lattice mismatch ratio of + 0.4%, for example, as the light absorption layer 105 is described as an example. However, the lattice mismatch is larger than 0% and +1. If it is within the range of .5% or less, crystal defects due to lattice mismatch are not abruptly introduced and can be applied as the light absorption layer 105.

  In the above embodiment, the case where the metalorganic molecular beam epitaxy method is used as the manufacturing method has been described. However, any growth method capable of forming an InGaAsSb layer may be used. For example, a molecular beam epitaxy method or a gas source molecular beam epitaxy method is used. It is obvious that the same effect can be obtained by a growth method such as a metal organic vapor phase epitaxy method.

Second Embodiment
Hereinafter, a second embodiment of the semiconductor light receiving element of the present invention will be described with reference to FIG.

[Configuration of semiconductor light receiving element]
First, a configuration example of the semiconductor light receiving element 600 of the present embodiment will be described with reference to FIG. FIG. 6 is a diagram illustrating a configuration example of the semiconductor light receiving element 600 according to the second embodiment.

  As shown in FIG. 6, the semiconductor light receiving element 600 is formed on the n-type InP substrate 601, the reflecting mirror (first reflecting mirror) 602 formed on the n-type InP substrate 601, and the reflecting mirror 602. n-type InGaAsP layer 603, undoped InGaAsP layer 604 formed on n-type InGaAsP layer 603, undoped InGaAsSb light absorption layer 605 formed on InGaAsP layer 604, and undoped formed on InGaAsSb light absorption layer 605 An InGaAsP layer 606 and an undoped InP layer 607 formed on the InGaAsP layer 606 are provided. These components 601 to 607 have the same functions as the components 101 to 107 shown in FIG.

  In FIG. 6, the band gap wavelengths of the n-type InGaAsP layer 603, the InGaAsP layer 604, and the p-type InGaAsP layer 606 are all 1.6 μm, for example.

  The InGaAsSb layer 605 is given by, for example, Sb composition ratio = 0.08, In composition ratio = 0.61, lattice mismatch with respect to InP = + 1.1%, band gap wavelength = 2.07 μm, and film thickness = 80 nm. It is done.

The reflecting mirror (first reflecting mirror) 602 has a semiconductor multilayer structure. In this multilayer structure, for example, an n-type InGaAsP layer with a band gap wavelength of 1.6 μm and a film thickness of 149 nm and an n-type InP layer with a band gap wavelength of 0.92 μm and a film thickness of 164 nm are formed as one pair. For example, 15 pairs are stacked in the reflecting mirror 602. In this case, the reflecting mirror 602 has a reflectance of about 92% for light having a wavelength of, for example, 2.05 μm. The wavelength of 2.05 μm corresponds to the wavelength at which the CO ₂ gas absorption line exists as shown in FIG.

  In FIG. 6, the Si / SiO 2 reflecting mirror (second reflecting mirror) 608 other than the components 601 to 607, the p-type electrode 609, the n-type electrode 610, and the Zn diffusion region 611 are referred to in the description of the manufacturing method described later. Is done.

[Method for Fabricating Semiconductor Light-Receiving Element]
Next, a method for manufacturing the semiconductor light receiving element 600 of the present embodiment will be described again with reference to FIGS.

  For the growth of the epitaxial wafer, the epitaxial wafer was formed by using, for example, the above-described organometallic molecular beam epitaxy as in the first embodiment.

  Then, a zinc (Zn) thermal diffusion process as shown in FIG. 6 is performed on a circular region having a diameter of 1100 μm on the upper surface of the epitaxial wafer (see Zn diffusion region 611 in FIG. 6).

Next, the surface of the epitaxial wafer is composed of silicon oxide (SiO ₂ ) and silicon (Si) so that the reflectance with respect to light having a wavelength of 2.05 μm is about 75% using, for example, an electron beam evaporation method. A reflecting mirror 608 was formed. Thereafter, the reflecting mirror 608 was removed in a ring-shaped region having an outer diameter = 1100 μm and an inner diameter = 1000 μm, and a p-type electrode 609 was formed in this region. Finally, the InP substrate 601 was polished to form the n-type electrode 610, whereby the planar semiconductor light-receiving element 600 of this embodiment was manufactured.

  In the semiconductor light-receiving element 600 manufactured in this way, the peak wavelength of the photocurrent was 2.05 μm and the quantum efficiency at the peak wavelength was 30% at the operating temperature = 20 ° C. and the bias voltage = −5V. The quantum efficiency in this case is 8% without the reflecting mirror 602, whereas the quantum efficiency of the semiconductor light receiving element 600 having the reflecting mirror 602 is 35%. From this, it was confirmed that the quantum efficiency almost as designed was obtained.

  When the signal light is away from the peak wavelength, the quantum efficiency rapidly decreases, but in the wavelength range of 2.02 μm to 2.06 μm, a quantum efficiency of 20% or more was confirmed.

From the above, according to the semiconductor light receiving element 600 of the present embodiment, although the wavelength range in which the quantum efficiency is increased can be reduced by increasing the reflectance, a high quantum efficiency can be obtained in the wavelength region where the reflectance is high. . The dark current is, for example, 1.05 ± 0.21 μA (134 ± 27 μA / cm ² ) when the operating temperature = 20 ° C. and the bias voltage = −0.5V. In the semiconductor light receiving element 600, good characteristics were obtained as a light receiving element operating in a wavelength region of 2 μm or more.

In this embodiment, the semiconductor light receiving element 600 using the Si / SiO ₂ film made of silicon oxide and silicon as the reflective mirror 608 has been described as an example. As long as it is a mirror, a multilayer film using other kinds of dielectrics or a multilayer film using a semiconductor may be used. Even in this case, it is obvious that the same effect as the semiconductor light receiving element 600 of the present embodiment can be obtained.

101,601 n-InP substrate 102,602 semiconductor multilayer mirror (n-InGaAsP / n-InP)
103,603 n-InGaAsP
104,604 InGaAsP
105,605 InGaAsSb
106,606 p-InGaAsP
107 p-InGaAs
108 silicon nitride 109,609 p-type electrode 110,610 n-type electrode 607 undoped InP layer 608 Si / SiO ₂ reflector 900 light-receiving element 901 n-type InP substrate 902 InAsP buffer layer 903 InGaAs light absorption layer 904 InAsP window layer

Claims (3)

A semiconductor light receiving element that converts an optical signal into an electrical signal,
An InP substrate;
An InGaAsSb light absorption layer formed on the InP substrate and having a compressive strain structure;
A first reflecting mirror and a second reflecting mirror for forming a resonator;
The first reflecting mirror is formed between the InP substrate and the InGaAsSb light absorbing layer and has a multilayer structure. When the Sb composition ratio of the InGaAsSb light absorption layer is x, x is in the range of 0 <x ≦ 0.3,
The lattice constant of the InGaAsSb light absorption layer is larger than the lattice constant of InP,
2. The semiconductor light receiving element according to claim 1, wherein P is in a range of 0% <P ≦ 1.5%, where P is a lattice mismatch ratio of InGaAsSb light absorption layer to InP.   The multilayer structure of the first reflecting mirror includes two or more elements of In, Ga, Al, As and P as constituent elements, and is configured to lattice match with InP. The semiconductor light receiving element described in 1.

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