JP2015015476A - Epitaxial wafer and manufacturing method of the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of an epitaxial wafer which can be grown with high efficiency while maintaining excellent crystal quality, and to provide the epitaxial wafer.SOLUTION: A manufacturing method of an epitaxial wafer comprises the steps of: preparing a semiconductor substrate; forming a type II multiple quantum well structure containing antimony (Sb) in one of or both of a paired layers in the number of pairs no fewer than 50 nor more than 700 on the substrate; and forming an InP surface layer. The processing steps from the start of the forming step of the multiple quantum well structure to the end of the formation step of the InP surface layer are performed in one growth tank such that a regrowth interface is not included, and all of the layers are formed by an all organic vapor phase epitaxy method using organic metal material.

Description

  The present invention relates to an epitaxial wafer of a III-V compound semiconductor and a method for manufacturing the same, and more specifically, an intermediate material for a high-quality light receiving element having light receiving sensitivity up to a long wavelength range in the near infrared. The present invention relates to an epitaxial wafer and a manufacturing method thereof.

A photodiode capable of obtaining a cutoff wavelength of 2 μm or more by forming an InGaAs / GaAsSb type II multiple quantum well structure on an InP substrate of a III-V compound semiconductor is disclosed (Non-patent Document). 1).
In addition, an LED having an emission wavelength of 2.14 microns formed by forming an InGaAs-GaAsSb type II quantum well structure on an InP substrate as an active layer has also been disclosed (Non-patent Document 2).
Furthermore, a semiconductor laser element having a GaInNAsSb quantum well structure has been disclosed (Patent Document 1). This GaInNAsSb quantum well structure is a single quantum well structure (that is, the number of pairs = 1).

JP 2005-197395 A

R. Sidhu, "A Long-Wavelength Photodiode on InP Using Lattice-Matched GaInAs-GaAsSb Type-II Quantum Wells, IEEE Photonics Technology Letters, Vol. 17, No. 12 (2005), pp. 271-2717 M.Peter, “Light-emitting diodes and laser diodes based on a Ga1-xInxAs / GaAs1-ySby type II superlattice on InP substrate” Appl. Phys. Lett., Vol.74, No.14 (1999), pp.1951 In the above-mentioned Non-Patent Document 1, it is assumed that distortion compensation is necessary for further wavelength increase. A photodetector having a cutoff wavelength of 2 μm to 5 μm by a strain compensation quantum well structure of Ga (In) AsSb—GaInAs (Sb) Has been proposed.

There is a great demand for development of photodiodes having light sensitivity in the near-infrared long wavelength range, for example, about 3 μm, because various organic substances and water have strong absorption bands in this wavelength range. In order to form the above type II (InGaAs / GaAsSb) multiple quantum well structure on an InP substrate, it is necessary to grow a GaAsSb layer that is easily phase-separated without phase separation. In addition, the light receiving layer of type II (InGaAs / GaAsSb) multiple quantum well structure in the above photodiode has a lower light absorption efficiency than a general light receiving layer such as an InGaAs single layer, thus improving the light receiving efficiency. Therefore, it is necessary to increase the number of InGaAs / GaAsSb pairs. In practice, to obtain sufficient efficiency, for example, 100 pairs or more of quantum wells are required.
In addition to the problems peculiar to the multiple quantum well structure, there are the following problems in the manufacture of InP-based light receiving elements. That is, in a light receiving element including a light receiving layer on an InP substrate, a window layer made of an InP-based material is provided on the outermost epitaxial layer. The window layer made of an InP-based material effectively acts to suppress dark current while preventing absorption of near infrared light on the incident surface side when the epitaxial layer is arranged on the incident surface side. Further, the technology for forming a passivation film on the surface of InP has more accumulation than the technology for forming a passivation film on the surface of another crystal, for example, the technology for forming it on the surface of InGaAs. That is, a technique for forming a passivation film on the surface of InP has been established, and dark current leakage on the surface can be easily suppressed. For the above reason, the InP window layer is arranged on the outermost surface. That is, it is necessary to form a semiconductor layer containing phosphorus (P), but the source of phosphorus differs depending on which crystal growth method is used. As will be described later, the safety of phosphorus compounds and the like attached to the inner wall of the growth chamber The issue becomes important.

When the quantum well structure is formed by the MOVPE method, for example, the growth of InGaAs and GaAsSb constituting the quantum well is switched by switching the source gas. Therefore, in the MOVPE method, an unnecessary gas immediately before switching remains, so when the number of pairs increases to about 50, an interface with a steep composition change cannot be obtained. It has been considered difficult to form while maintaining good quality.
In Non-Patent Document 2, a type II InGaAs / GaAsSb quantum well structure is formed by the MOVPE method. At this time, trimethylindium (TMIn), trimethylgallium (TMGa), and arsine (AsH ₃ ) are used as InGaAs raw materials. On the other hand, trimethylgallium (TMGa), tertiary butylarsine (TBAs), and triethylantimony (TESb) are used as raw materials for GaAsSb. However, with this method, it is difficult to increase the number of pairs of type II InGaAs / GaAsSb multiple quantum well structures. Also in Non-Patent Document 2, the number of pairs of quantum wells having a multiple quantum well structure is limited to attempts within the range of 10 or more and 20 or less, and details of quality evaluation are not discussed. In the fabrication of multi-quantum well structures, defects and roughness on the surface of crystal growth are caused by local strain and non-periodicity caused by imperfect arrangement of atoms during the formation of the crystal growth interface of different materials. This is thought to be due to the atomic bond. That is, the size of the growth surface defects and roughness become more prominent as the number of pairs in the multiple quantum well structure increases and the number of interfaces increases. When the number of pairs in the multiple quantum well structure is 20 or less, for example, defects and Even if the roughness is suppressed to less than about 1 micron and the number of pairs is 50 or more even if there is no major problem in the flatness of the crystal surface, for example, the size of defects and roughness is up to about 10 microns. In general, the problem of the increase in the flatness of the crystal surface occurs.
Patent Document 1 does not deal with a multiple quantum well structure, and discloses only GaInNAsSb having a single quantum well structure (number of pairs 1). Therefore, increasing the number of pairs in the quantum well structure, for example, increasing the number of pairs to 50 or more, is not recognized. This is due in part to the large difference between the lattice constant of GaInNAsSb constituting the quantum well structure and the lattice constant of GaAs as the substrate. That is, the degree of lattice mismatch of GaInNAsSb, defined by the formula of (GaInNAsSb lattice constant−GaAs lattice constant) / GaAs lattice constant, is about 1.7%, and this lattice mismatch of about 1.7%. In terms of the degree of matching, the number of pairs in the quantum well structure can be limited to about 5 at most. If the number of pairs in the quantum well is 50 or more, crystal defects occur due to the difference in lattice constants, misfit dislocations occur, and the crystal quality is reduced. It will greatly deteriorate. For this reason, those skilled in the art no longer have the opportunity to come up with a multiple quantum well structure based on Patent Document 1.
In addition, when a light-receiving element is manufactured by forming a type II InGaAs / GaAsSb multiple quantum well structure by the MOVPE method, the surface state of the multiple quantum well structure is not satisfactory. Therefore, it has never been studied to provide an InP window layer on the outermost epitaxial layer.

On the other hand, compared with the MOVPE method, the MBE (molecular beam epitaxy) method can instantaneously switch the molecular beam with a shutter. For this reason, automatic switching of microcomputer-controlled valves is possible, and it has been considered that deposition by the MBE method is almost inevitable for the growth of a steep interface and a high-quality multiple quantum well structure.
In particular, when considering the problem of crystal growth of a GaAsSb layer containing Sb that easily undergoes phase separation, a crystal growth method with strong non-equilibrium is necessary for epitaxial growth while preventing phase separation. For this reason, the MBE method which is a crystal growth method with strong non-equilibrium is suitable. Actually, the MBE method is used to form a GaAsSb layer (Non-patent Document 1).
However, the MOVPE method is a growth method with high film forming efficiency, and if a multi-quantum well structure having a large number of pairs can be grown by the MOVPE method, it is very useful industrially.
Although the MBE method is advantageous for forming a multiple quantum well structure containing GaAsSb, it is not easy to grow the above-described InP window layer while maintaining industrially high safety by the MBE method. Absent. The reason is that in the MBE method, a solid material is used as a material, and therefore solid phosphorus is used as a material for phosphorus (P) in the InP window layer. For this reason, as described above, solid phosphorus, which is a residue after film formation, adheres to the wall of the film formation tank as the film formation proceeds. Solid phosphorus raw materials are highly ignitable, and there is a high possibility that they will ignite when the raw materials are frequently replenished in the MBE method and equipment maintenance is performed, and countermeasures corresponding to these are required. In addition, when phosphorus raw materials are used, a phosphorus exhaust abatement device is further required.

The light receiving element is manufactured by processing an intermediate material using an epitaxial wafer obtained by epitaxially growing a semiconductor layer including a light receiving layer and a surface layer on a substrate. The above growth method is a method for manufacturing an epitaxial wafer including a multiple quantum well structure or the like as the intermediate material.
By the way, in the light receiving element, a plurality of pixels are arranged two-dimensionally or one-dimensionally and used for an imaging device or the like. However, separation between individual pixels must be ensured.
It is well known that there are the following two methods for separating pixels.
One is a planar photodiode in which pixels are formed by selective diffusion from the surface of the epitaxial wafer. In this planar photodiode, when an impurity is introduced from the opening of the selective diffusion mask pattern to the light receiving layer by selective diffusion, a pn junction is formed at the tip of the impurity region (in the light receiving layer). A pixel is separated from an adjacent pixel by a region not selectively diffused corresponding to the non-opening. In the planar type, a pn junction is not formed on the epitaxial wafer before selective diffusion. Only after selective diffusion is performed, a pn junction is formed for each pixel.
The other is a mesa-type light receiving element that forms a groove by performing mesa etching from the surface of the epitaxial wafer and separates a pixel from an adjacent pixel by the groove. In this mesa type light receiving element, a pn junction is formed over the entire wafer by doping during epitaxial growth. For this reason, when an epitaxial wafer is manufactured, the pn junction is uniformly formed on the entire wafer. In the mesa-type light receiving element, the manufactured epitaxial wafer is subjected to mesa etching to form a groove for separating adjacent pixels.

  Under the present situation, the present invention provides a method for producing an epitaxial wafer as an intermediate material, and an epitaxial wafer capable of efficiently growing a multiple quantum well structure having a large number of pairs while ensuring good crystal quality. The main purpose is to provide In particular, a method of forming an InP window layer located on the upper layer of a multiple quantum well structure having a large number of pairs while having good crystallinity, and an InP window layer having good crystallinity were formed. An object is to provide the epitaxial wafer.

The method for producing an epitaxial wafer of the present invention produces a wafer having an epitaxial layered product of III-V compound semiconductors. The manufacturing method includes a step of preparing a substrate of a III-V compound semiconductor, and a type II multiple quantum well structure including antimony (Sb) in one or both of a pair of layers on the substrate, A step of forming with 50 to 700 pairs, a step of forming an InP surface layer constituting the surface layer of the epitaxial multilayer on the multiple quantum well structure, and a step of forming a pn junction by doping From the start of the formation process of the multi-quantum well structure to the end of the formation process of the InP surface layer, it is processed in one growth tank so as not to include the regrowth interface, It is characterized in that it is formed by an all-organic vapor phase growth method using an organometallic gas raw material comprising the above compound.
Here, the all-organic vapor phase growth method refers to a growth method using an organic metal raw material composed of a compound of an organic substance and a metal for all the raw materials used for the vapor phase growth, and is also referred to as an all organic MOVPE method.

As a result of intensive studies, the inventors have found that a multi-quantum well structure having 50 or more pairs of high-quality III-V compound semiconductor quantum wells can be formed by the all-organic MOVPE method. Generally thinks as follows.
In the above method, the crystal film on the substrate is grown using the all organic MOVPE method. At this time, in the all organic MOVPE method, the molecular weight of the raw material molecules is large in all of the raw materials to be used, so that it is easily decomposed and is located closer to the substrate as compared with the normal MOVPE method in which inorganic raw materials are also used. The organometallic gas is easily decomposed into the shape necessary for growth and easily contributes to crystal growth. The present invention relies heavily on this point.

The above will be described in detail below. After the first compound constituting the quantum well pair is grown to a predetermined thickness, the carrier gas (hydrogen) is introduced while being sucked and exhausted by a vacuum pump, and the source gas of the first compound is stopped by an electromagnetic valve. On the substrate, only the first compound grows with a little inertia. The little inertia is caused by the fraction of the organometallic gas that is in close contact with the substrate and is in a range close to the substrate temperature. Even in that case, the compound growing on the substrate basically has the composition of the first compound.
Further, the metal organic vapor phase epitaxy method has a small non-equilibrium property, but grows without phase separation if the substrate temperature is low even in the case of a compound that is easily phase-separated. By stopping the source gas and flowing the carrier gas while pulling with a vacuum pump, the crystal growth of the first compound is stopped after the above-described slight inertia growth.
Next, when a sufficient concentration is reached near the substrate by flowing a source gas (organometallic gas) matched to the second compound that forms a pair while flowing the carrier gas, crystal growth of the second compound starts. After the second compound is grown to a predetermined thickness, if the electromagnetic valve of the source gas of the second compound is stopped while the carrier gas (hydrogen) is introduced while being sucked and exhausted by a vacuum pump, the second compound Only grow with a little inertia. The little inertia is caused by the fraction of the organometallic gas that is in close contact with the substrate and is in a range close to the substrate temperature. Even in that case, the compound growing on the substrate basically has the composition of the second compound. If a multi-quantum well structure is formed by the all-organic MOVPE method through the above procedure, a heterointerface having a sharp composition change can be obtained. Operations such as opening and closing of the electromagnetic valve and forced exhaust of the vacuum pump are all controlled automatically by a computer and performed automatically.
The major reason why a steep hetero interface can be obtained over 50 pairs or more according to the present invention is that, by using the all-organic MOVPE method, the source gas located almost in contact with the substrate is completely decomposed. To contribute to crystal growth. In the conventional MOVPE method so far, the raw material gas of the compound to be formed includes those with low decomposition efficiency, and a larger amount of raw material gas is required to achieve the target crystal growth. . However, since the decomposition efficiency is small, the raw material gas located in the range almost in contact with the substrate contains a raw material gas that could not be decomposed and a gas such as an intermediate product that is in the middle of the decomposition. It is considered that a steep hetero interface could not be obtained because it was incorporated into the crystal growth and adversely affected. However, in the all-organic MOVPE method, since the decomposition efficiency of the source gas is good and the reaction product in the intermediate stage is not easily generated, the source gas near the substrate involved in the crystal growth is inhibited by “abrupt composition change”. It was found that “the remaining raw material gas” can be expected to be absent in the all-organic MOVPE method.
Further, as a major reason why a steep hetero interface can be obtained over 50 pairs or more according to the present invention, for example, in InGaAs and GaAsSb constituting a multiple quantum well structure in which the number of pairs exceeds 50, An all-organic MOVPE method using an organometallic raw material as the As raw material can be used. When forming a multi-quantum well structure, the As raw material is not switched at the interface (boundary surface) between both InGaAs and GaAsSb, so it is considered that a steep quantum well structure interface can be formed. This becomes more significant as the number of pairs in the quantum well structure increases, and it is possible to obtain good characteristics with a multiple quantum well structure having a large number of pairs.
In summary, by focusing on the raw material system for crystal growth and optimizing the crystal growth conditions, multiple organic MOVPE methods can be used to multiplex 50 pairs or more with high quality crystal layers and steep composition interfaces. The quantum well structure can be grown with high efficiency. However, if the number of pairs of quantum wells is excessive, lattice defects are accumulated, surface roughness occurs in the outermost layer crystal such as the window layer, and dark current increases. By suppressing the number of pairs of quantum wells to 700 pairs or less, a light receiving element having a sufficiently low dark current can be obtained.

Further, in the all-organic MOVPE method, solid phosphorus (P) is not used as a raw material when growing an InP surface layer (sometimes referred to as an InP window layer). As a result, the semiconductor layer is formed in the same growth tank consistently from the multiple quantum well structure, so it does not include a regrowth interface that contains a large amount of impurities (oxygen and carbon are distributed at a high concentration at the outside air exposed interface). Therefore, a semiconductor element having excellent characteristics can be formed. For example, when a multi-quantum well structure is formed by the MBE method, and the InP window layer is finally formed, there are the above-mentioned ignition problems and growth temperature problems, and in order to switch to another growth method such as the MOVPE method. It was necessary to get out of the MBE growth room once. However, in the all organic MOVPE method, the semiconductor layer can be grown in the same growth tank from the multiple quantum well structure to the end of the growth of the InP window layer.
In the growth of an InP layer by the all-organic MOVPE method, the present inventors decomposed and crystallized in a temperature range of 400 ° C. or higher and 560 ° C. or lower by using a total organic source gas such as tertiary butylphosphine as a phosphorus source. It was found that it can contribute to growth. In the case where the InP window layer is formed in a temperature range of less than 400 ° C., the decomposition efficiency of the source gas is greatly reduced, so that the impurity concentration in the InP layer is increased and a high quality InP window layer cannot be obtained. . Further, when the InP window layer was formed at a temperature exceeding 560 ° C., the crystal of the multiple quantum well structure located in the lower layer, particularly the layer containing antimony (Sb), was damaged by heat and the crystallinity deteriorated. It has been found that by setting the temperature in the range of 400 ° C. or more and 560 ° C. or less, a semiconductor element having a high-quality InP window layer can be formed without impairing the crystallinity of the multiple quantum well structure. In addition, since no solid material is used as the raw material of P, it is safe in terms of safety and the like, and also in terms of growth efficiency, it is more advantageous than other growth methods, particularly the MBE method. Further, when an InP window layer is formed in the light receiving element, it is easy to form a passivation protection film on the surface of InP, and thus dark current leakage can be easily suppressed.

The above temperature is very important in epitaxial wafers containing type II multi-quantum well structures containing antimony (Sb) in one or both layers. It is necessary to grow a phase containing Sb, for example, a GaAsSb layer without phase separation. For this reason, after forming a multiple quantum well structure, the above temperature must be kept low until the InP window layer has been grown. For example, when the above temperature exceeds 560 ° C., for example, about 600 ° C., the GaAsSb layer located in the lower layer causes phase separation, which impairs crystallinity.
Further, Sb is known as an element that exhibits a surfactant effect in a semiconductor material such as silicon. The element showing the surfactant effect has a tendency to accumulate on the surface of the semiconductor material, although the reason has not yet been elucidated. The light receiving layer having a multiple quantum well structure of (InGaAs / GaAsSb) or (GaInNAs / GaAsSb) contains Sb. For this reason, when the temperature exceeds a high temperature, for example, 560 ° C., Sb accumulates sequentially on the surface of the layer during the growth during the film formation following the multi-quantum well structure. It also accumulates on the surface. The problem at this time is that the crystal surface becomes rough and the leakage current increases at the rough surface, resulting in an increase in dark current. Further, after forming an Sb-integrated layer, for example, when an InP window layer 5 is formed thereon, Sb in the layer is attracted to the interface between the InP window layer and the lower layer, and the Sb-enriched layer Is formed. In the present invention, since it grows by the all-organic vapor phase growth method using an organic metal raw material that is easily decomposed at a relatively low temperature, it can be epitaxially grown at a low temperature. As a result, even if there is a layer containing Sb, A good epitaxial laminate can be obtained.
Here, the above-mentioned temperature refers to the substrate surface temperature being monitored by a pyrometer including an infrared camera and an infrared spectrometer. Accordingly, although it is the substrate surface temperature, strictly speaking, it is the temperature of the epitaxial layer surface in a state where a film is formed on the substrate. There are various names such as a substrate temperature, a growth temperature, and a film formation temperature, and all refer to the monitored temperatures.

From the start of the formation process of the multiple quantum well structure to the end of the formation process of the InP surface layer, there can be no process of forming a pn junction in the multiple quantum well structure.
Thereby, when manufacturing a light receiving element using this epitaxial wafer, after that, a selective diffusion mask pattern is formed on the epitaxial wafer, and impurities such as zinc (Zn) are removed from the opening of the selective diffusion mask pattern. Selective diffusion can be performed. By selective diffusion from this opening, a pn junction can be formed in the multiple quantum well structure. The region where impurities are selectively diffused from the opening constitutes a pixel and is isolated from the adjacent pixel by a region under the non-opening that is not selectively diffused. As a result, a planar light receiving element is formed.
The term “epitaxial wafer” used in the description of the present invention is limited to the following. That is, after the formation of the multiple quantum well structure to the end of the formation process of the InP surface layer, it is formed by the all-organic MOVPE method in one growth tank, and then the structure of the epitaxial multilayer is added or changed. This refers to a wafer that has not been subjected to any special treatment. Therefore, for example, the intermediate material after the selective diffusion mask pattern is formed on the epitaxial wafer of the present invention and the impurity is selectively diffused from the opening is often called an epitaxial wafer, but in the description of the present invention, the impurity is selected. The wafer after diffusion is not an object of the epitaxial wafer.

In the step of forming the multiple quantum well structure, a pn junction can be formed in the multiple quantum well structure by doping.
The method of doping impurities during epitaxial growth in order to form a pn junction in a multiple quantum well structure is the same as impurity doping to a buffer layer or the like located near the substrate. That is, in the all-organic MOVPE method, an organic metal raw material is used also for impurity doping. TeESi (tetraethylsilane) can be used for n-type doping. In addition, DEZn (diethyl zinc) can be used for p-type doping. The impurity concentration distribution by doping from the InP surface layer to the pn junction having the multiple quantum well structure is formed in accordance with a well-known concentration distribution in a mesa type light receiving element. As a result, the InP surface layer is doped with a high concentration of impurities so that the pixel electrode is in ohmic contact.
The above pn junction should be interpreted broadly as follows. In the multiple quantum well structure, the impurity concentration in the region on the substrate side is low enough to be regarded as an intrinsic semiconductor (referred to as i region), and between the region doped with the impurity on the surface layer side and the i region. This also includes the joint formed in the above. That is, the pn junction may be a pi junction or an ni junction, and further includes a case where the p concentration or the n concentration in the pi junction or ni junction is very low.
As described above, when this epitaxial wafer is used as an intermediate material of a light receiving element, since the impurity doping for forming the pn junction is performed during the epitaxial growth of the multiple quantum well structure, the pixel having the pn junction by mesa etching. Can be formed separately.

In the formation process of the multiple quantum well structure, a pair of In _x Ga _1-x As (0.38 ≦ x ≦ 0.68) and GaAs _1-y Sb _y (0.36 ≦ y ≦ 0.62), or _{Ga 1-u in u N v} as 1-v (0.4 ≦ u ≦ 0.8,0 <v ≦ 0.2) and _{GaAs 1-y} Sb y in (0.36 ≦ y ≦ 0.62) A type II multiple quantum well structure composed of a pair can be formed.
As a result, a light receiving element having a wavelength determined from the energy band gap of 2 μm to 5 μm can be manufactured efficiently and in large quantities while maintaining a low impurity concentration and good crystallinity.

  In the step of forming the multiple quantum well structure, a multiple quantum well structure can be formed using TEGa (triethylgallium) or TMGa (trimethylgallium) as a Ga (gallium) raw material. This makes it possible to form a high-quality multiple quantum well structure with a low impurity concentration in the multiple quantum well structure and to maintain good crystallinity, and to manufacture efficiently and in large quantities.

  In the step of forming the multiple quantum well structure, a multiple quantum well structure can be formed by using TEIn (triethylindium) or TMIn (trimethylindium) as an In (indium) raw material. As a result, while maintaining good crystallinity, a high-quality multiple quantum well structure can be formed, and can be manufactured efficiently and in large quantities.

  In the step of forming the multiple quantum well structure, a multiple quantum well structure can be formed by using TBAs (tertiary butylarsine) or TMAs (trimethylarsenic) as the As (arsenic) raw material. This makes it possible to form a high-quality multiple quantum well structure with a low impurity concentration in the multiple quantum well structure and to maintain good crystallinity, and to manufacture efficiently and in large quantities.

  In the step of forming the multiple quantum well structure, a multiple quantum well structure can be formed using TESb (triethylantimony) or TMSb (trimethylantimony) as a raw material for Sb (antimony). This makes it possible to form a high-quality multiple quantum well structure with a low impurity concentration in the multiple quantum well structure and to maintain good crystallinity, and to manufacture efficiently and in large quantities.

In the step of forming the multiple quantum well structure, the multiple quantum well structure is preferably formed at a temperature of 400 ° C. or higher and 560 ° C. or lower.
According to this, the crystal film is grown on the substrate at a predetermined temperature of 400 ° C. to 560 ° C., or near or within a predetermined temperature range by the all organic MOVPE method. At this time, when the multiple quantum well structure is formed at a predetermined temperature of 400 ° C. to 560 ° C., near the predetermined temperature or in a predetermined temperature range, the decomposition efficiency of the source gas is good in the all organic MOVPE method. Since the organometallic gas located at is efficiently decomposed into a shape necessary for growth and contributes to the growth of the crystal film, the steepness of the composition at the heterointerface can be obtained. That is, it is possible to obtain a crystal growth surface of a multiple quantum well structure that is clean and excellent in flatness, and a multiple quantum well structure that has remarkably excellent periodicity and crystallinity. When a multi-quantum well structure is formed in a temperature range of less than 400 ° C., the decomposition efficiency of the source gas is greatly reduced, so that the steepness of the composition at the heterointerface cannot be obtained, and it is clean and excellent in flatness. A crystal growth surface having a multiple quantum well structure and a multiple quantum well structure having excellent periodicity and crystallinity could not be obtained. Furthermore, when a multiple quantum well structure is formed in a temperature range exceeding 560 ° C., phase separation occurs in the crystal growth of GaAsSb, and therefore, the crystal growth surface of the multiple quantum well structure that is clean and excellent in flatness, and excellent A multiple quantum well structure with periodicity and crystallinity could not be obtained.

An epitaxial wafer of the present invention includes an III-V compound semiconductor epitaxial laminate formed on a III-V compound semiconductor substrate. This epitaxial wafer includes a type II multiple quantum well structure included in the epitaxial multilayer, an InP surface layer constituting a surface layer of the epitaxial multilayer, and a pn junction formed by doping, and includes a type II multiple quantum well. The well structure includes one or both of the paired layers containing antimony (Sb) and is composed of 50 pairs or more and 700 pairs or less, and oxygen (O) is formed between the multiple quantum well structure and the InP surface layer. And no regrowth interface containing carbon (C) at a high concentration.
Thus, an epitaxial wafer having good crystallinity can be provided with excellent economic efficiency.

It is possible not to include a pn junction in a type II multiple quantum well structure.
Thus, when manufacturing a light receiving element using this epitaxial wafer, a selective diffusion mask pattern is formed on this epitaxial wafer, and impurities such as zinc (Zn) are selectively diffused from the opening of the selective diffusion mask pattern. Thus, a pn junction can be formed in the multiple quantum well structure. As a result, a planar light receiving element can be obtained.

The type II multiple quantum well structure may have a pn junction formed by doping.
Thereby, an epitaxial wafer for the intermediate material of the mesa light receiving element can be obtained.

The multiple quantum well structure is a pair of In _x Ga _1-x As (0.38 ≦ x ≦ 0.68) and GaAs _1-y Sb _y (0.36 ≦ y ≦ 0.62), or Ga _{1 − u in u N v as 1-} v (0.4 ≦ u ≦ 0.8,0 <v ≦ 0.2) and a pair of _{GaAs 1-y Sb y (0.36} ≦ y ≦ 0.62) in, It can be configured as a type II multiple quantum well structure.
Thereby, an epitaxial wafer for a light receiving element having light receiving sensitivity in the near infrared region can be obtained.

  According to the epitaxial wafer manufacturing method and the like of the present invention, a multiple quantum well structure having a large number of pairs can be efficiently grown while ensuring good crystal quality. As a result, a light-receiving element including a light-receiving layer having a type II multiple quantum well structure and an InP window layer and having a light-receiving sensitivity up to a long wavelength region in the near infrared region can be efficiently manufactured without generating a regrowth interface. Is possible.

It is sectional drawing for demonstrating the manufacturing method of the multiple quantum well structure in Embodiment 1 of this invention. It is a figure for demonstrating the apparatus for manufacturing the multiple quantum well structure of FIG. FIG. 3 is a partial plan view of the apparatus of FIG. 2. It is explanatory drawing of formation of the multiple quantum well structure by all the organic MOVPE method, (a) has a big temperature fall from a wafer surface to space by the flow of source gas, (b) is the organometallic gas which contacts a wafer surface It is a figure for demonstrating this molecule | numerator. It is sectional drawing for demonstrating the light receiving element which is a semiconductor element in Embodiment 2 of this invention. It is sectional drawing for demonstrating the light receiving element in which the multiple quantum well structure was formed by MBE method, and the InP window layer was formed by MOVPE method. It is a flowchart of the manufacturing method of the light receiving element of FIG. It is a figure in Example 3 which shows the relationship between the light reception sensitivity and dark current, and the number of pairs of quantum wells.

(Embodiment 1)
FIG. 1 is a cross-sectional view showing a multiple quantum well structure manufactured by an epitaxial wafer manufacturing method according to Embodiment 1 of the present invention. The multiple quantum well structure 3 is formed on an n-type InP substrate 1 doped with S with an InGaAs buffer layer 2 interposed. The quantum well pair in the multiple quantum well structure 3 is composed of GaAsSb 3a having a thickness of 5 nm and InGaAs 3b having a thickness of 5 nm. Both are non-doped. GaAsSb3a is formed in direct contact with the InGaAs buffer layer. In the present embodiment, the multiple quantum well structure 3 includes 250 pairs of quantum wells. The present embodiment is characterized in that the multiple quantum well structure 3 composed of 250 pairs of quantum wells is formed by the all-organic MOVPE method.

  FIG. 2 shows a piping system of the all-organic MOVPE film forming apparatus 70 in which the multiple quantum well structure 3 is formed. A quartz tube 35 is disposed in the reaction chamber (chamber) 30, and a raw material gas is introduced into the quartz tube 35. A substrate table 51 is disposed in the quartz tube 35 so as to be rotatable and airtight. The substrate table 51 is provided with a heater 51h for heating the substrate. The temperature of the surface of the wafer 10 a during film formation is monitored by the infrared temperature monitoring device 20 through the window 21 provided in the ceiling portion of the reaction chamber 30. This monitored temperature is a temperature at the time of growth or a temperature called a film forming temperature or a substrate temperature. In the production method of the present invention, when the multiple quantum well structure is formed at a temperature of 400 ° C. or higher and 560 ° C. or lower, 400 ° C. or higher and 560 ° C. or lower are temperatures measured by this temperature monitor. The forced exhaust from the quartz tube 35 is performed by a vacuum pump.

The source gas is supplied by a pipe communicating with the quartz tube 35. The all organic MOVPE method is characterized in that all raw material gases are supplied in the form of an organometallic gas. In FIG. 2, source gases such as impurities are not specified, but impurities are also introduced in the form of an organometallic gas. The raw material of the organometallic gas is put in a thermostat and kept at a constant temperature. Hydrogen (H ₂ ) and nitrogen (N ₂ ) are used as the carrier gas. The organometallic gas is conveyed by a carrier gas, and is sucked by a vacuum pump and introduced into the quartz tube 35. The amount of carrier gas is accurately adjusted by an MFC (Mass Flow Controller). Many flow controllers, solenoid valves, and the like are automatically controlled by a microcomputer.

A method for manufacturing the wafer 10 shown in FIG. 1 will be described. First, an n-type InP buffer layer 2 is epitaxially grown on a S-doped n-type InP substrate 1 to a thickness of 10 nm. TeESi (tetraethylsilane) was used for n-type doping. At this time, TMIn (trimethylindium) and TBP (tertiary butylphosphine) are used as the source gas. The InP buffer layer 2 may be grown using an inorganic raw material PH ₃ (phosphine). In the growth of the InP buffer layer 2, even if the growth temperature is about 600 ° C. or less than about 600 ° C., the crystallinity of the InP substrate located in the lower layer is not deteriorated by heating at about 600 ° C. However, when the InP window layer described in the second embodiment is formed, since the multiple quantum well structure containing GaAsSb is formed in the lower layer, the substrate temperature is strictly limited to a temperature range of 400 ° C. or more and 560 ° C. or less, for example. Need to be maintained. The reason is that when heated to about 600 ° C., the crystallinity of GaAsSb is greatly deteriorated due to heat damage, and when the InP window layer is formed at a temperature lower than 400 ° C., the decomposition efficiency of the source gas is greatly increased. Therefore, the impurity concentration in the InP layer increases, and a high-quality InP window layer cannot be obtained. Next, an n-type doped InGaAs layer is grown on the InP buffer layer 2 to a thickness of 0.15 μm (150 nm). This InGaAs layer is also included in the buffer layer 2 in FIG.

  Next, a type II multiple quantum well structure 3 having InGaAs / GaAsSb as a pair of quantum wells is formed. GaAsSb3a in the quantum well is preferably 5 nm thick, and InGaAs3b is preferably 5 nm thick. In FIG. 1, a multi-quantum well structure 3 is formed by stacking 250 pairs of quantum wells. In the film formation of GaAsSb3a, triethylgallium (TEGa), tertiary butylarsine (TBAs) and trimethylantimony (TMSb) are used. For InGaAs3b, TEGa, TMIn, and TBAs can be used. These source gases are all organometallic gases, and the molecular weight of the compound is large. Therefore, it can be completely decomposed at a relatively low temperature of 400 ° C. or higher and 560 ° C. or lower and contribute to crystal growth. The composition change at the interface of the quantum well can be made steep in the multiple quantum well structure 3 by all organic MOVPE.

As a raw material of Ga (gallium), TEGa (triethylgallium) or TMGa (trimethylgallium) may be used, but TEGa is preferable. This is because TEGa can reduce the impurity concentration in the crystal. In particular, the concentration of carbon that is an impurity inside the quantum well layer is 1 × 10 ¹⁶ cm ⁻³ or more when TMGa is used, but can be less than 1 × 10 ¹⁶ cm ⁻³ when TEGa is used. . As a raw material of In (indium), TMIn (trimethylindium) or TEIn (triethylindium) may be used, but TMIn is preferable. This is because TMIn is superior in controllability of In composition. As a raw material of As (arsenic), TBAs (tertiary butylarsine) or TMAs (trimethylarsenic) may be used, but TBAs is preferable. This is because TBAs can reduce the impurity concentration in the crystal. In particular, the carbon concentration that is an impurity inside the quantum well layer is 1 × 10 ¹⁶ cm ⁻³ or more when TMAs is used, but can be less than 1 × 10 ¹⁶ cm ⁻³ when TBAs is used. . The raw material for Sb (antimony) may be TMSb (trimethylantimony), TESb (triethylantimony), TIPSb (triisopropylantimony), or TDMASb (tridimethylaminoantimony). TESb is good. This is because TESb can reduce the impurity concentration in the crystal. In particular, the carbon concentration that becomes an impurity inside the quantum well layer is 1 × 10 ¹⁶ cm ⁻³ or more when TMSb, TIPSb, or TDMASb is used, but less than 1 × 10 ¹⁶ cm ⁻³ when TESb is used. can do. As a result, a semiconductor element having a low impurity concentration in the multiple quantum well layer and excellent crystallinity can be obtained. As a result, for example, when used in a light receiving element, a light receiving element with a small dark current and a high sensitivity can be obtained. Furthermore, an imaging apparatus that can capture a clearer image can be obtained using the light receiving element.

Next, the flow state of the source gas when the multiple quantum well structure 3 is formed by the all organic MOVPE method will be described. FIG. 3 is a plan view showing a flow in which the source gas is conveyed through the piping, introduced into the quartz tube 35, and exhausted. Although the source gas shows only three types of piping, the basic structure is controlled by opening and closing the electromagnetic valve even if there are more than ten types of source gas.
The flow rate of the source gas is controlled by a flow rate controller (MFC) shown in FIG. 2, and the flow into the quartz tube 35 is turned on and off by opening and closing the electromagnetic valve. The quartz tube 35 is forcibly exhausted by a vacuum pump. As shown in FIG. 3, there is no portion in which the flow of the raw material gas is stagnant, and the flow is performed automatically and smoothly. Therefore, the composition is switched quickly when forming the quantum well pair.
As shown in FIG. 3, since the substrate table 51 rotates, the temperature distribution of the source gas does not have the directivity as on the inflow side or the outlet side of the source gas. Further, since the wafer 10a revolves on the substrate table 51, the flow of the source gas near the surface of the wafer 10a is in a turbulent state, and even the source gas near the surface of the wafer 10a contacts the wafer 10a. Except for the raw material gas, it has a large velocity component in the flow direction from the introduction side to the exhaust side. Therefore, most of the heat flowing from the substrate table 51 through the wafer 10a to the source gas is always exhausted together with the exhaust gas. For this reason, a large temperature gradient or temperature step is generated in the vertical direction from the wafer 10a through the surface to the source gas space.
Furthermore, in the embodiment of the present invention, the substrate temperature is heated to a low temperature range of 400 ° C. or more and 560 ° C. or less. When the all organic MOVPE method using TBAs or the like as a raw material at such a low temperature substrate surface temperature is used, since the decomposition efficiency of the raw material is good, the growth of the multiple quantum well structure with the raw material gas flowing in a range very close to the wafer 10a The source gas that contributes to is limited to those efficiently decomposed into the form necessary for growth.

FIG. 4A is a diagram showing the flow of organometallic molecules and the flow of temperature, and FIG. 4B is a schematic diagram of organometallic molecules on the substrate surface. These diagrams are used to explain the importance of setting the surface temperature in order to obtain a steep composition change at the heterointerface of the multiple quantum well structure.
The surface of the wafer 10a is set at a monitored temperature. However, when the raw material gas space is slightly entered from the wafer surface, a sudden temperature drop or a large temperature step occurs as described above. Therefore, in the case of a raw material gas having a decomposition temperature of T1 ° C., the substrate surface temperature is set to (T1 + α), and α is determined in consideration of variations in temperature distribution and the like. In a situation where there is a sudden large temperature drop or temperature step from the surface of the wafer 10a to the source gas space, when large-sized organometallic molecules flow through the wafer surface as shown in FIG. It is considered that the compound molecules that contribute to the growth are limited to the range in contact with the surface and the thickness range of several organometallic molecules from the surface. Therefore, as shown in FIG. 4B, organometallic molecules in the range in contact with the wafer surface and molecules located within the thickness range of several organometallic molecules from the wafer surface are mainly used for crystal growth. Contributingly, it is considered that the organometallic molecules outside it are discharged out of the quartz tube 35 with almost no decomposition. When the organometallic molecules near the surface of the wafer 10a are decomposed and crystal growth occurs, the organometallic molecules located outside enter the replenishment.
In other words, the range of the organometallic molecules that can participate in crystal growth is limited to a thin source gas layer on the surface of the wafer 10a by making the wafer surface temperature slightly higher than the temperature at which the organometallic molecules decompose. it can.

From the above, when the source gas suitable for the chemical composition of the pair is switched by the electromagnetic valve and forcedly evacuated by the vacuum pump, after the crystal of the previous chemical composition is grown with slight inertia, Thus, it is possible to grow a crystal having a switched chemical composition without being affected by the source gas. As a result, the composition change at the hetero interface can be made steep. This means that the previous source gas does not substantially remain in the quartz tube 35, and the source gas that contributes to the growth of the multiple quantum well structure with the source gas flowing in a range very close to the wafer 10a is: This is due to the fact that it is limited to those efficiently decomposed into the shape necessary for growth (factor 1). That is, as can be seen from FIG. 3, when one layer of the quantum well is formed, the electromagnetic valve is opened and closed while forcibly evacuating with a vacuum pump, and when the source gas for forming the other layer is introduced, a little Although there are organometallic molecules that participate in crystal growth with inertia, the molecules in one layer that replenishes them are almost exhausted and gone. The closer the wafer surface temperature is to the decomposition temperature of the organometallic molecules, the smaller the range of organometallic molecules participating in crystal growth (range from the wafer surface).
When forming this multi-quantum well structure, phase growth occurs in the GaAsSb layer of the multi-quantum well structure when grown in a temperature range of about 600 ° C., and the crystal growth surface of the multi-quantum well structure that is clean and excellent in flatness, and A multiple quantum well structure having excellent periodicity and crystallinity cannot be obtained. For this reason, the growth temperature is set to a temperature range of 400 ° C. or more and 560 ° C. or less (factor 2). Factor 1 strongly depends on this (factor 3).

(Embodiment 2)
FIG. 5 is a cross-sectional view showing a semiconductor element manufactured using the epitaxial wafer according to the second embodiment of the present invention. The semiconductor element 10 is a light receiving element of a planar photodiode. The steps up to the stage of n-type InP substrate 1 / buffer layer 2 / type II multiple quantum well structure 3 (InGaAs3a / GaAsSb3b) are the same as those in FIG. On the type II multiple quantum well structure 3, an InGaAs layer 4 responsible for adjusting the diffusion concentration distribution, which will be described in detail later, is located, and an InP window layer 5 is located on the InGaAs layer 4. . A p-type impurity Zn is introduced into a predetermined region from the surface of the InP window layer 5 to provide a p-type region 15, and a pn junction or a pi junction is formed at the tip thereof. A reverse bias voltage is applied to the pn junction or pi junction to form a depletion layer, and the charge due to photoelectron conversion is captured, so that the brightness of the pixel corresponds to the amount of charge. The p-type region 15 or the pn junction or pi junction is a main part constituting the pixel. The p-side electrode 11 that is in ohmic contact with the p-type region 15 is a pixel electrode, and reads out the above charges for each pixel with an n-side electrode (not shown) having a common ground potential. The surface of the InP window layer around the p-type region 15 is covered with an insulating protective film 9.
One point is to continue the growth in the same film formation chamber or quartz tube 35 by the all organic MOVPE method until the formation of the InP window layer 5 after the formation of the multiple quantum well structure. That is, before the InP window layer 5 is formed, the wafer 10a is not taken out from the film forming chamber, and the InP window layer 5 is not formed by another film forming method. One point. That is, since the InGaAs layer 4 and the InP window layer 5 are continuously formed in the quartz tube 35, the interface 17 is not a regrowth interface. For this reason, the concentrations of oxygen, carbon, and silicon are all equal to or lower than a predetermined level, and no charge leakage occurs at the intersection line between the p-type region 15 and the interface 17.

In the present embodiment, as shown in FIG. 5, a non-doped InGaAs layer 4 having a thickness of 1.0 μm is formed on the multiple quantum well structure 3. In this InGaAs layer 4, after the InP window layer 5 is formed, when a p-type impurity Zn is introduced from the InP window layer 5 so as to reach the multiple quantum well structure 3 by a selective diffusion method, a high concentration of Zn becomes a multiple quantum. When entering the well structure 3, the crystallinity is damaged. For this reason, this InGaAs layer 4 may be called a diffusion concentration distribution adjusting layer. In the InGaAs layer 4, the Zn concentration is 5 on the side of the multiple quantum well structure 3 even if it is a high concentration of about 1 × 10 ¹⁸ cm ^{−3 to} 3 × 10 ¹⁹ cm ⁻³ on the InP window layer side. It is preferable that the concentration distribution be rapidly reduced to × 10 ¹⁶ cm ⁻³ or less. By inserting the InGaAs layer 4, it is possible to make the Zn diffusion concentration distribution as described above. A p-type impurity region 15 is formed by the selective diffusion described above, and a pn junction or a pi junction is formed at the tip thereof. By forming the diffusion concentration distribution adjusting layer of InGaAs, the electric resistance of the light receiving element can be lowered even if the impurity concentration (Zn concentration) is low. By reducing the electrical resistance, it is possible to improve the responsiveness and obtain a moving image with good image quality.
On the InGaAs diffusion concentration distribution adjusting layer 4, an undoped InP window layer is epitaxially grown to a thickness of 0.8 μm by the total organic MOVPE method continuously with the wafer 10 a placed in the same quartz tube 35. As described above, trimethylindium (TMIn) and tertiary butylphosphine (TBP) are used for the source gas. By using this source gas, the growth temperature of the InP window layer 5 can be made 400 ° C. or more and 560 ° C. or less, and further 535 ° C. or less. As a result, the GaAsSb 3a having the multiple quantum well structure located under the InP window layer 5 is not damaged by heat, and the crystallinity of the multiple quantum well is not impaired. When forming the InP window layer, since the multiple quantum well structure containing GaAsSb is formed in the lower layer, it is necessary to strictly maintain the substrate temperature within a range of, for example, a temperature of 400 ° C. or more and 560 ° C. or less. The reason is that when heated to about 600 ° C., the crystallinity of GaAsSb is greatly deteriorated due to heat damage, and when the InP window layer is formed at a temperature lower than 400 ° C., the decomposition efficiency of the source gas is greatly increased. Therefore, the impurity concentration in the InP layer increases, and a high-quality InP window layer cannot be obtained.

As described above, conventionally, it has been necessary to form a multiple quantum well structure by the MBE method. However, in order to grow the InP window layer 5 by the MBE method, it is necessary to use a solid raw material as the phosphorus raw material, which is problematic in terms of safety. There was also room for improvement in terms of manufacturing efficiency. FIG. 6 is a diagram showing a light receiving element 110 in which a multiple quantum well structure 103 and an InGaAs layer 104 are formed by MBE method, and then are exposed to the atmosphere, and an InP window layer 105 is formed by MOVPE method. The structure of the light receiving element 110 is almost the same in composition as the light receiving element 10 in FIG. That is, it is formed of an epitaxial layer of InP substrate 101 / multiple quantum well structure 103 / InGaAs diffusion concentration distribution adjusting layer 104 / InP window layer 105. The p-type region 115 constituting the main part of the pixel, the p-side electrode 111 constituting the pixel electrode, the insulating protective film 109, and the like are the same as the light receiving element in FIG.
The difference is an interface 117 between the InGaAs layer 104 and the InP window layer 105. The interface 117 is a regrowth interface once exposed to the atmosphere. By secondary ion mass spectrometry, the oxygen concentration is 1 × 10 ¹⁷ cm ⁻³ or more, and the carbon concentration is 1 × 10 ¹⁷ cm ⁻³ or more. And it can specify by satisfy | filling at least 1 among silicon concentration 1x10 < ¹⁷ > cm < ^-3 > or more. The regrowth interface 117 forms a cross line 117a with the p-type region 115, and a charge leak occurs at the cross line 117a, so that the image quality is remarkably deteriorated.
In addition, for example, when the InP window layer 105 is simply MOVPE, phosphine (PH ₃ ) is used as a raw material of phosphorus, so that the decomposition temperature is high, and the occurrence of damage due to the heat of GaAsSb located in the lower layer is induced to cause multiple quantum wells. It will harm the crystallinity of the structure.

  FIG. 7 is a flowchart of a method for manufacturing an epitaxial wafer serving as an intermediate material of the light receiving element 10 of FIG. According to this manufacturing method, only the organic metal gas is used as the source gas (factor 3), the growth temperature is lowered (factor 2), and the formation of the InP window layer 5 is consistently completed. Since it is formed in the film chamber or the quartz tube 35, it is important not to have a recrystallization interface (factor 4). As a result, an epitaxial wafer serving as an intermediate material for manufacturing a photodiode having a light receiving sensitivity in a wavelength region of 2 μm to 5 μm with little charge leakage and excellent crystallinity can be manufactured efficiently and in large quantities.

  In the present embodiment, the multiple quantum well structure is type II. In the type I quantum well structure, when a semiconductor layer having a small band gap energy is sandwiched between semiconductor layers having a large band gap energy and light receiving sensitivity is provided in the near infrared region, the band gap of the semiconductor layer having a small band gap energy The upper limit wavelength (cutoff wavelength) of the light receiving sensitivity is determined. That is, transition of electrons or holes due to light is performed in a semiconductor layer having a small band gap energy (direct transition). In the case of this structure, the material for extending the cut-off wavelength to a longer wavelength region is very limited within the III-V compound semiconductor. On the other hand, in the type II quantum well structure, when two different semiconductor layers having the same Fermi energy are alternately stacked, the conduction band of the first semiconductor and the valence band of the second semiconductor are obtained. The upper limit of the wavelength (cutoff wavelength) of the light receiving sensitivity is determined. That is, transition of electrons or holes by light is performed between the valence band of the second semiconductor and the conduction band of the first semiconductor (indirect transition). For this reason, the energy of the valence band of the second semiconductor is made higher than that of the first semiconductor, and the energy of the conduction band of the first semiconductor is made lower than the energy of the conduction band of the second semiconductor. By doing so, it is easier to realize a longer wavelength of light receiving sensitivity than in the case of direct transition in one semiconductor.

Example 1
The light receiving element (example of the present invention) shown in FIG. 5 was manufactured by the method according to the first and second embodiments for manufacturing the epitaxial wafer of the present invention, and preliminary evaluation was performed. Evaluation items and evaluation results are as follows. Further, the comparative example is the light receiving element shown in FIG. 6, which uses the MBE method to form the multiple quantum well structure in the epitaxial wafer, and uses the MOVPE method to form the arsine in the V group material by using the MOVPE method. (AsH ₃ ) and phosphine (PH ₃ ) were used. The growth temperature of the InP window layer was 535 ° C. in the example of the present invention, but 600 ° C. in the comparative example.
1. Surface state of InP window layer In the example of the present invention, it was possible to obtain a clean and excellent surface. On the other hand, in the comparative example, the InP window layer had a strong surface roughness.
2. X-ray diffraction of a multiple quantum well structure The periodicity of a type II multiple quantum well structure was evaluated by an X-ray diffraction method. The evaluation was performed based on the half width at a predetermined peak of the X-ray diffraction pattern. In the example of the present invention, the half width of the peak value of the X-ray diffraction pattern of the multiple quantum well structure was 80 seconds. On the other hand, in the comparative example, the half width of the peak of the X-ray diffraction pattern was 150 seconds. From this, it was found that the periodicity and crystallinity of the multi-quantum well structure were remarkably excellent in the inventive examples.
3. PL emission intensity In the example of the present invention, a good PL emission intensity could be obtained in a wavelength region of 2.4 μm. On the other hand, in the comparative example, it was not possible to obtain an evaluable PL light emission.

(Example 2)
The light-receiving element shown in FIG. 5 was tested for the test samples manufactured by the manufacturing method according to the present invention. Examples A1 to A7 of the present invention, and test samples manufactured by a manufacturing method different from the present invention and comparative examples B1 to B3 And dark current of the light receiving element were evaluated. The dark current is a value at a diameter of 100 μm at Vr = −5 volts.
(Invention Sample A1): Growth of type II MQW light-receiving layer (temperature: 510 ° C.) and InP window layer (temperature: 510 ° C.) by all organic MOVPE
(Invention Sample A2): Growth of Type II MQW light-receiving layer (temperature 380 ° C.) and InP window layer (temperature 510 ° C.) by all organic MOVPE
(Invention Sample A3): Growth of type II MQW light-receiving layer (temperature 400 ° C.) and InP window layer (temperature 510 ° C.) by all organic MOVPE
(Invention Sample A4): Growth of type II MQW light-receiving layer (temperature 450 ° C.) and InP window layer (temperature 510 ° C.) by all organic MOVPE
(Invention Sample A5): Growth of type II MQW light-receiving layer (temperature 535 ° C.) and InP window layer (temperature 510 ° C.) by all organic MOVPE
(Invention Sample A6): Growth of type II MQW light-receiving layer (temperature 560 ° C.) and InP window layer (temperature 510 ° C.) by all organic MOVPE
(Invention Sample A7): Growth of type II MQW light-receiving layer (temperature 580 ° C.) and InP window layer (temperature 510 ° C.) by all organic MOVPE
In the inventive examples A1 to A7, when the type II type (InGaAs / GaAsSb) MQW is grown by all organic MOVPE, the temperature is changed to a range of 380 ° C. to 580 ° C. Other conditions are the same.
(Comparative Example B1: Method according to Non-Patent Document 1): Growth of type II MQW light-receiving layer by MBE (temperature 400 ° C.) and growth of InP window layer by normal MOVPE (temperature 600 ° C.)
(Comparative Example B2: Method according to Non-Patent Document 2): Growth of type II MQW light-receiving layer by normal MOVPE (temperature 510 ° C.) and growth of InP window layer by total organic MOVPE (temperature 510 ° C.)
(Comparative Example B3): Growth of type II MQW light-receiving layer by normal MOVPE (temperature 600 ° C.) and growth of InP window layer by total organic MOVPE (temperature 510 ° C.)
In the comparative example, type II (InGaAs / GaAsSb) MQW is grown by the MBE method (Comparative Example B1) and the normal MOVPE method (Comparative Examples B1 and B2).
Tables 1 and 2 show the production conditions of the above-described specimens and the results of the evaluation.

According to Table 1, in Comparative Examples B1 to B3, the half width of the MQW X-ray diffraction peak is 150 seconds (Comparative Example B1), 150 seconds (Comparative Example B2), and 170 seconds (Comparative Example B3). The result was wide and the crystallinity was not good. Moreover, about Comparative Examples B1-B3, PL light emission with a wavelength of 2.4 micrometers did not arise. Furthermore, as for the surface properties of the InP window layer, the surface roughness of the strength occurred in Comparative Examples B1 to B3. The dark current in the photodiode was 5 μA in Comparative Example B1 and 4 μA in Comparative Example B2. As for the surface properties of the InP window layer, when many defects or roughness of about 10 μm or more are confirmed, it is determined that “surface roughness has occurred”, and when the defects and roughness of the above size are hardly confirmed, “clean and flat It was determined that the surface had excellent properties.
On the other hand, as shown in Tables 1 and 2, in Invention Examples A1 to A7, when the growth temperature of MQW is extremely low, such as 380 ° C. (Invention Example A2), and 580 ° C. (Invention of the present invention). When it was extremely high as in Example A7), the full width at half maximum of the X-ray diffraction peak was 125 seconds and 150 seconds. PL light emission did not occur in Examples A2 and A7 of the present invention. In other examples of the present invention A1, A3 to A6, the half width of the X-ray diffraction peak was as narrow as 80 seconds and 55 seconds to 95 seconds, the crystallinity was good, and PL emission was also generated. . As for the surface properties of the InP window layer, the surfaces other than Invention Examples A2 and A7 were clean and had excellent flatness. Further, with respect to the dark current, except for Examples A2 and A7, 0.4 μA (Invention Example A1), 0.9 μA (Invention Example A3), 0.7 μA (Invention Example A4), 0.4 μA (present) Invention Example A5) and 0.8 μA (Invention Example A6), low dark current characteristics were obtained.
According to the results of the present example, by the method of the present invention, it is possible to obtain good crystallinity by growing type II (InGaAs / GaAsSb) MQW with all organic MOVPE at a temperature of 400 ° C. to 560 ° C. In addition, the surface of the InP window layer was excellent in flatness, and as a result, dark current could be kept low. Even in the case of the production method (crystal growth by the all organic MOVPE method) belonging to the widest range of the present invention, good results could not be obtained when grown at a temperature outside the temperature range of 400 ° C to 560 ° C. . Moreover, when the type II type (InGaAs / GaAsSb) MQW is grown without using the all organic MOVPE method as in Comparative Examples B1 to B3, the crystallinity deteriorates and the surface properties of the InP window layer deteriorate due to the deterioration. It was confirmed.

Example 3
In Invention Example A1 of Example 2, the number of quantum well pairs was changed in the range of 50 to 1000. That is, the number of pairs of quantum wells was changed in the structure of the light receiving element shown in FIG. Other growth conditions are the same.
(Invention Sample A1-1): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs: 50 pairs)
(Invention Sample A1-2): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs: 150 pairs)
(Invention Sample A1-3): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs: 250 pairs)
(Invention Sample A1-4): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs: 350 pairs)
(Invention Sample A1-5): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs: 450 pairs)
(Invention Sample A1-6): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs: 700 pairs)
(Invention Sample A1-7): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs: 850 pairs)
(Invention Sample A1-8): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs: 1000 pairs)
For Inventive Examples A1-1 to A1-8, the dark current and sensitivity of the light receiving element were evaluated. The dark current is a value at a diameter of 100 μm at Vr = 5 volts. The sensitivity is a value with respect to light having a diameter of 1 mm at a reverse bias voltage Vr = 5 volts and a wavelength of 2000 nm. The evaluation results are shown in Table 3.

In Inventive Examples A1-1 to A1-6, the InP window layer had a clean and excellent surface. The dark current of the light receiving element was as low as 300 nA to 600 nA, and good dark current characteristics were obtained. In Invention Examples A1-7 and A1-8, surface roughness occurred in the InP window layer. The dark current of the light-receiving element was as high as 2 μA (Invention Sample A1-7) and 5 μA (Invention Sample A1-8), resulting in dark current failure.
On the other hand, in Examples A1-1 to A1-6 of the present invention, the sensitivity increased from 0.1 A / W to 0.75 A / W as the number of pairs was increased from 50 to 700. In inventive examples A1-7 and A1-8, the sensitivities were 0.7 A / W and 0.6 A / W, respectively.
FIG. 8 shows the relationship between the photosensitivity and dark current and the number of quantum well pairs. When the number of pairs is 850 or more, the light receiving sensitivity is high, but the dark current increases. There is a range of the number of pairs in which both the light receiving sensitivity and the dark current are in a practical level range.
Detailed data will be described later in Example 4. When a light receiving element array having a structure corresponding to the light receiving elements of Examples A1-1 to A1-8 of the present invention was manufactured and an imaging device was manufactured, A1-3 Only when the light receiving element array corresponding to A1-6 was used, a clearer image was successfully captured by setting the environmental temperature of the imaging apparatus to 0 ° C. or lower using the cooling mechanism. On the other hand, when the light receiving elements A1-1, A1-2, A1-7, and A1-8 are used, a clear image can be obtained even when the environmental temperature of the imaging apparatus is set to 0 ° C. or lower using the cooling mechanism. I couldn't take an image.

Example 4
In the present invention examples A1-3, A1-4, and A1-5 of Example 3, the raw materials used when forming the type II multiple quantum well structure 3 in which InGaAs / GaAsSb is a quantum well pair are changed. I let you. That is, the raw material used for the fabrication of the quantum well in the structure of the light receiving element shown in FIG. 5 was changed. The structure of the manufactured light receiving element is the same.
(Invention Sample A1-3-1): Type II MQW light-receiving layer made of all organic MOVPE (the number of pairs is 250 pairs, and TEGa, TMIn, TBAs, and TMSb are used as raw materials)
(Invention Sample A1-3-2): Type II MQW light-receiving layer made of all organic MOVPE (number of pairs is 250 pairs, TEGa, TMIn, TBAs, and TESb are used as raw materials)
(Invention Sample A1-3-3): Type II MQW light-receiving layer made of all organic MOVPE (the number of pairs is 250 pairs, and TEGa, TMIn, TMAs, and TESb are used as raw materials)
(Invention Sample A1-3-4): Type II MQW light-receiving layer made of all organic MOVPE (the number of pairs is 250 pairs, and TEGa, TEIn, TBAs, and TESb are used as raw materials)
(Invention Sample A1-3-5): Type II MQW light-receiving layer made of all organic MOVPE (250 pairs, TMGa, TMIn, TBAs, TESb used as raw material)
(Invention Sample A1-4-1): Type II MQW light-receiving layer (350 pairs, TEGa, TMIn, TBAs, TMSb is used as a raw material) by all organic MOVPE
(Invention Sample A1-4-2): Type II MQW light-receiving layer (350 pairs, TEGa, TMIn, TBAs, and TESb are used as raw materials) by all organic MOVPE
(Invention Sample A1-5-1): Type II MQW light-receiving layer made of all organic MOVPE (450 pairs, TEGa, TMIn, TBAs, TMSb used as raw material)
(Invention Sample A1-5-2): Type II MQW light-receiving layer made of all organic MOVPE (450 pairs, TEGa, TMIn, TBAs, TESb used as raw material)
Invention Examples A1-3-1, A1-3-3, A1-3-3, A1-3-4, A1-3-5, A1-4-1, and A1-4-2 , And A1-5-1 and A1-5-2, the light receiving element array was manufactured under the same conditions, the imaging device was manufactured, and the imaging state of the imaging device was evaluated. In the light receiving element array, light receiving elements (pixels) are arranged in a size of 320 × 256, and the imaging device has a total of about 80,000 pixels. The dark current is a value at a diameter of 100 μm at Vr = 5 volts. The evaluation results are shown in Table 4.

A1-3-3 which is a test body using TMAs as an As raw material in the inventive example, A1-3-4 which is a test body using TEIn as an In raw material in the inventive example, and a Ga raw material in the inventive example In A1-3-5, which is a test body using TMGa, the dark current at a light receiving diameter of 100 μm of the manufactured light receiving element is 3 μA to 5 μA, which is lower than that of Example A1-3-2. Increased and the characteristics deteriorated. On the other hand, in the present invention example, A1-3-3 which is a test body using TMAs as an As raw material, and in the present invention example, A1-3-4 which is a test body using TEIn as an In raw material, and the present invention example In A1-3-5, which is a test body using TMGa as a Ga raw material, the sensitivity is 0.1 A / W to 0.3 A / W, and the sensitivity is lower than that of the test body A1-3-2. The characteristics deteriorated.
In A1-3-2, A1-4-2, and A1-5-2, which are test bodies using TESb as the Sb raw material in the present invention example, the dark current at the light receiving diameter of 100 μm of the manufactured light receiving element is Compared with A1-3-1, A1-4-1, and A1-5-1, which are test specimens using TMSb as the Sb raw material in the present invention example, respectively, the dark current is reduced to 40 nA to 50 nA. And very good dark current characteristics were obtained. On the other hand, in A1-3-2, A1-4-2, and A1-5-2, which are test bodies using TESb as an Sb raw material in the present invention, the sensitivity is 0.75 A / W to 0.9 A / W, and the sensitivity could be increased as compared with A1-3-1, A1-4-1, and A1-5-1, which are test bodies using TMSb as the Sb raw material in the present invention, respectively. .
Invention Examples A1-3-1, A1-3-3, A1-3-3, A1-3-4, A1-3-5, A1-4-1, and A1-4-2 When the imaging device is manufactured using the light receiving element arrays manufactured in A1-5-1 and A1-5-2, the dark current density of the light receiving element is 0.5 mA / cm ² or less. Only when a light receiving element array corresponding to A1-3-1 and A1-4-2 was used, a clear image was successfully captured without using a cooling mechanism. That is, only when the light receiving element arrays A1-3-1 and A1-4-2, which are examples of the present invention in which the dark current density of the light receiving elements is 0.5 mA / cm ² or less, are used, the environmental temperature of the imaging apparatus For example, it has succeeded in capturing a clear image even in a more practical temperature range such as 0 ° C. or more and 40 ° C. or less.

(Other embodiments, etc.)
In the embodiments and examples of the present invention, only the light receiving element has been described as the semiconductor element in which the epitaxial wafer of the present invention is used. However, the semiconductor element in which the epitaxial wafer of the present invention is used or the epitaxial element having the configuration requirements of the present invention. If it is a wafer, it will not be limited to a light receiving element, A light emitting element (semiconductor laser) etc. may be sufficient. In these light-emitting elements or the like, usually, impurity doping is performed during epitaxial growth to form a pn junction or the like. Also, the light receiving element may be an epitaxial wafer for a mesa type light receiving element in which impurity doping is normally performed during epitaxial growth to form a pn junction. It may have other functions and uses. In these, a pn junction or the like is usually formed by doping impurities during epitaxial growth.

  Although the embodiments of the present invention have been described above, the embodiments of the present invention disclosed above are merely examples, and the scope of the present invention is not limited to these embodiments. 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 epitaxial wafer manufacturing method and the like of the present invention, a multiple quantum well structure having a large number of pairs can be efficiently grown while ensuring good crystal quality. As a result, an InP-based light receiving element having a light receiving layer having a type II multiple quantum well structure and an InP window layer and having a light receiving sensitivity up to a long wavelength region in the near infrared region is consistently formed by the same organic MOVPE method. All epitaxial growth films can be grown in the film chamber. For this reason, not only a high-quality light receiving element can be obtained except for the regrowth interface, but also the efficiency improvement inherent to the film forming method and the efficiency improvement by continuous growth can be obtained. Furthermore, since no solid is used as the raw material of P, there is no concern about safety.

1 InP substrate, 2 buffer layer (InP and / or InGaAs), 3 type II multiple quantum well structure, 3a GaAsSb layer, 3b InGaAs layer, 4 InGaAs layer (diffusion concentration distribution adjusting layer), 5 InP window layer, 9 insulation protection Film, 10 product including multiple quantum well structure (intermediate product), 10a wafer (intermediate product), 11 p-side electrode (pixel electrode), 15 p-type region, 17 interface between InGaAs layer and InP window layer, 20 infrared temperature Monitor device, 21 reaction chamber window, 30 reaction chamber, 35 quartz tube, 51 substrate table, 51h heater, 70 all organic MOVPE film forming device.

Claims (11)

A method for producing a wafer having an epitaxial stack of III-V compound semiconductors,
Preparing a substrate of a III-V compound semiconductor;
Forming a type II multi-quantum well structure containing antimony (Sb) in one or both of the paired layers on the substrate with 50 to 700 pairs;
A step of forming an InP surface layer constituting a surface layer of the epitaxial multilayer on the multiple quantum well structure, and a step of forming a pn junction by doping;
From the start of the formation process of the multi-quantum well structure to the end of the formation process of the InP surface layer, it is processed in one growth tank so as not to include a regrowth interface, and all layers are treated with hydrocarbons and metal elements. A method for producing an epitaxial wafer, characterized in that it is formed by an all-organic vapor phase growth method using an organometallic gas raw material comprising a compound of   2. The method of manufacturing an epitaxial wafer according to claim 1, wherein the pn junction is formed in the multiple quantum well structure. In the step of forming the multiple quantum well structure, a pair of In _x Ga _1-x As (0.38 ≦ x ≦ 0.68) and GaAs _1-y Sb _y (0.36 ≦ y ≦ 0.62), or _{, Ga 1-u In u N} v as 1-v (0.4 ≦ u ≦ 0.8,0 <v ≦ 0.2) and _{GaAs 1-y Sb y (0.36} ≦ y ≦ 0.62) 3. The method of manufacturing an epitaxial wafer according to claim 1, wherein a type II multiple quantum well structure composed of a pair of   The multi-quantum well structure is formed by using TEGa (triethyl gallium) or TMGa (trimethyl gallium) as a Ga (gallium) raw material in the step of forming the multi-quantum well structure. 4. The method for producing an epitaxial wafer according to any one of 3 above.   The multi-quantum well structure is formed by using TEIn (triethylindium) or TMIn (trimethylindium) as a source of In (indium) in the step of forming the multiple quantum well structure. 5. The method for producing an epitaxial wafer according to claim 4.   The multi-quantum well structure is formed by using TBAs (tertiary butylarsine) or TMAs (trimethylarsenic) as a raw material of As (arsenic) in the step of forming the multi-quantum well structure. The manufacturing method of the epitaxial wafer of any one of 1-5.   2. The multiple quantum well structure is formed by using TESb (triethylantimony) or TMSb (trimethylantimony) as a raw material of Sb (antimony) in the step of forming the multiple quantum well structure. 6. The method for producing an epitaxial wafer according to any one of 6 above.   8. The epitaxial wafer according to claim 4, wherein in the step of forming the multiple quantum well structure, the multiple quantum well structure is formed at a temperature of 400 ° C. or more and 560 ° C. or less. Production method. An epitaxial wafer comprising an epitaxial layered body of III-V compound semiconductor formed on a substrate of III-V compound semiconductor,
A type II multiple quantum well structure included in the epitaxial stack;
An InP surface layer constituting the surface layer of the epitaxial multilayer, and a pn junction formed by doping;
In the type II multiple quantum well structure, one or both of the layers includes antimony (Sb), and is composed of 50 pairs or more and 700 pairs or less,
An epitaxial wafer characterized in that there is no regrowth interface containing oxygen (O) and carbon (C) at a high concentration between the multiple quantum well structure and the InP surface layer.   The epitaxial wafer according to claim 9, wherein the pn junction is formed in the multiple quantum well structure. The multiple quantum well structure is a pair of In _x Ga _1-x As (0.38 ≦ x ≦ 0.68) and GaAs _1-y Sb _y (0.36 ≦ y ≦ 0.62), or Ga _{1 -u in u N v as 1-} v (0.4 ≦ u ≦ 0.8,0 <v ≦ 0.2) and a pair of _{GaAs 1-y Sb y (0.36} ≦ y ≦ 0.62), The epitaxial wafer according to claim 9, wherein the epitaxial wafer has a type II multiple quantum well structure.

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