Semi-insulating gallium arsenide single crystal substrate, substrate with epitaxial layer and method for producing a semi-insulating gallium arsenide single crystal

Abstract

The semi-insulating gallium arsenide single-crystal substrate is a semi-insulating gallium arsenide single-crystal substrate with a circular first principal surface, wherein the diameter of the semi-insulating gallium arsenide single-crystal substrate is 95 mm or more and 205 mm or less, and the light absorption coefficient of the semi-insulating gallium arsenide single-crystal substrate with respect to near-infrared light at a wavelength of 940 nm is 1.5 cm. -1 or less, the number of etch pits per square centimeter formed on the first main surface in an etch test by immersion of the semi-insulating gallium arsenide single-crystal substrate in molten potassium hydroxide at 500 °C for 10 minutes is 300 or less, and a specific resistivity of the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C by the Van der Pauw method 1.0 × 10 8 Ω·cm or more.

Description

Technical field

[0001] The present disclosure relates to a semi-insulating gallium arsenide single crystal substrate, a substrate with an epitaxial layer and a method for producing a semi-insulating gallium arsenide single crystal. State of the art

[0002] US Patent Publication No. 2020 / 0190696 (PTL 1) and US Patent Publication No. 2020 / 0190697 (PTL 2) disclose the following features of a gallium arsenide single-crystal substrate that can be used in an optical device. In other words, PTL 1 and PTL 2 each disclose a gallium arsenide single-crystal substrate in which the light absorption coefficient with respect to near-infrared light at a wavelength of 940 nm is 3 cm -1or less, and the dislocation density (hereinafter also referred to as "EPD" - Etch Pit Density) is the number of etch pits per square centimeter formed in an etch test on a primary surface, 1000 cm² -2 or less, and a gallium arsenide single-crystal substrate where the light absorption coefficient is 6 cm -1 and the EPD 500 cm -2 or less. US Patent Publication No. 2013 / 0320242 (PTL 3) discloses a doped gallium arsenide single crystal in which the light absorption coefficient with respect to near-infrared light at a wavelength of 1000 nm is 2 cm. -1 or less, and the single crystal has a low light absorption coefficient, enabling its use in an optical device. WO 2019 / 008663 (PTL 4) discloses a gallium arsenide single-crystal substrate where the EPD is 10 cm -2 or more and 10000 cm -2or less, and an efficient adjustment of the insulation properties or the conductivity properties can be made. List of cited documents Patent literature PTL 1: US Patent Publication No. 2020 / 0190696 PTL 2: US Patent Publication No. 2020 / 0190697 PTL 3: US Patent Publication No. 2013 / 0320242 PTL 4: WO 2019 / 008663 Summary of the invention

[0003] The semi-insulating gallium arsenide single-crystal substrate according to the present disclosure is a semi-insulating gallium arsenide single-crystal substrate with a circular first principal surface. The diameter of the semi-insulating gallium arsenide single-crystal substrate is 95 mm or more and 205 mm or less. The light absorption coefficient of the semi-insulating gallium arsenide single-crystal substrate with respect to near-infrared light with a wavelength of 940 nm is 1.5 cm⁻¹. -1or less. The number of etch pits per square centimeter formed on the primary surface in an etching test by immersing the semi-insulating gallium arsenide single-crystal substrate in molten potassium hydroxide at 500 °C for 10 minutes is 300 or less. The resistivity of the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C in a Hall test using the Van der Pauw method, is 1.0 × 10⁻⁶. 8 Ω·cm or more.

[0004] The substrate with an epitaxial layer according to the present disclosure comprises the semi-insulating gallium arsenide single-crystal substrate and an epitaxial layer arranged on the first principal surface. The epitaxial layer comprises an infrared emission layer.

[0005] The process for producing a semi-insulating gallium arsenide single crystal according to the present disclosure is a process for producing a semi-insulating gallium arsenide single crystal using a vertical boat process, wherein the production process comprises preparing a single-crystal growth apparatus comprising at least one cylindrical crucible and a heating element that heats the crucible, receiving a seed crystal in a lower section of the crucible and receiving gallium arsenide mass in an upper section compared to the seed crystal in the crucible, heating the crucible by the heating element to partially melt the gallium arsenide and the seed crystal, thereby not only obtaining a gallium arsenide melt but also bringing the gallium arsenide melt and a residue of the seed crystal into contact, and growing a crystal on the seed crystal in the gallium arsenide melt.to obtain a semi-insulating gallium arsenide single crystal. The obtaining of a semi-insulating gallium arsenide single crystal is carried out by fulfilling the following formulas 4, 5 and 6: 0.20°C / mm≤X≤0.30°C / mm X+0.0012°C / mm2×Y≤Z1≤X+0.0024°C / mm2×Y 0.26°C / mm≤Z2≤0.42°C / mm where in Formula 4, Formula 5 and Formula 6, X represents a temperature gradient along an axial direction of the crucible, measured with a cross-sectional area between the crystal and the gallium arsenide melt as the center point, and a unit of the temperature gradient °C / mm, Y represents a distance from the interface to a first reference point in the crystal and the unit of the distance is mm, Z1 represents a temperature gradient along an axial direction of the crucible, measured with the first reference point as the center, and the unit of the temperature gradient is °C / mm, and Z2 represents a temperature gradient along an axial direction of the crucible, measured with the first reference point as its center at a distance of 50 mm from the interface to the first reference point, and the unit of the temperature gradient is °C / mm. Brief description of the drawings Fig. Figure 1 is an illustrative diagram describing a location (area) to be measured for measuring each property of the light absorption coefficient and EL2 concentration of a semi-insulating gallium arsenide single crystal substrate according to the present embodiment. Fig. Figure 2 is an illustrative diagram that describes a measuring point (measuring range) for measuring the dislocation density of a semi-insulating gallium arsenide single crystal substrate according to the present embodiment. Fig. Figure 3 is an illustrative diagram describing a pattern for a Hall measurement, wherein the pattern is prepared with a central section of a semi-insulating gallium arsenide single-crystal substrate according to the present embodiment to measure each property of the resistivity, carrier concentration and electron mobility of the semi-insulating gallium arsenide single-crystal substrate. Fig. Figure 4 is a diagram describing a residual stress distribution on a first main surface of a semi-insulating gallium arsenide single crystal substrate according to the present embodiment. Fig. Figure 5 is an illustrative diagram describing a substrate with an epitaxial layer according to the present embodiment. Fig. Figure 6 is a flowchart illustrating an overview of a process for the preparation of a semi-insulating gallium arsenide single-crystal substrate according to the present embodiment. Fig. Figure 7 is an illustrative diagram relating to a process for producing a semi-insulating gallium arsenide single crystal according to the present embodiment and describing a step for obtaining a semi-insulating gallium arsenide single crystal using a single-crystal fabrication apparatus. Fig. Figure 8 is another illustrative diagram relating to a method for producing a semi-insulating gallium arsenide single crystal according to the present embodiment and describing a step for obtaining a semi-insulating gallium arsenide single crystal using a single-crystal fabrication apparatus. Detailed description [The problem to be solved by the present revelation]

[0006] In recent years, stricter requirements have been placed on the use of gallium arsenide single-crystal substrates as substrates for optical devices, particularly vertical cavity surface-emitting lasers (VCSELs) and similar applications, with regard to high near-infrared transmittance and low dislocation capability. For example, the gallium arsenide single-crystal substrates of PTL 1 and PTL 2 are required to exhibit a lower light absorption coefficient in the near-infrared range, or a lower EPD. The gallium arsenide single-crystal substrate of PTL 3 must not only have a lower light absorption coefficient in the near-infrared region but also a lower EPD.The gallium arsenide single crystal substrate of PTL 4 is not specified with respect to the light absorption coefficient towards near-infrared light when used in an optical device, however, at least one gallium arsenide single crystal substrate classified as a high-resistance semi-insulating substrate must have a lower EPD.

[0007] To date, no semi-insulating gallium arsenide single-crystal substrate has been realized for an optical device such as a VCSEL that meets both the properties of a low light absorption coefficient and a low EPD with respect to near-infrared light, and there is a need to develop such a substrate.

[0008] In light of the foregoing considerations, it is an object of the present invention to provide a semi-insulating gallium arsenide single crystal substrate, a substrate with an epitaxial layer and a method for producing a semi-insulating gallium arsenide single crystal suitable for an optical device that requires high near-infrared light transmittance and low dislocation capability, such as a VCSEL. [Advantageous effect of the present disclosure]

[0009] According to the above, it is possible to provide a semi-insulating gallium arsenide single crystal substrate, a substrate with an epitaxial layer, and a method for producing a semi-insulating gallium arsenide single crystal suitable for an optical device requiring high near-infrared transmittance and low dislocation capability, such as a VCSEL. [Description of exemplary implementations]

[0010] First, an embodiment of the present disclosure is described. The inventors have conducted intensive investigations to solve the aforementioned problems and have arrived at the present disclosure. Initially, the inventors focused on the following: Not only is the carrier concentration kept low to achieve high transmittance for near-infrared light in a semi-insulating gallium arsenide single-crystal substrate, but the frequent occurrence of dislocations, which is to be feared at a low carrier concentration, is also suppressed by a method for producing a semi-insulating gallium arsenide single crystal.In particular, the inventors have produced a semi-insulating gallium arsenide single crystal in which the occurrence of dislocations is suppressed as far as possible by critically controlling the growth temperature of the semi-insulating gallium arsenide single crystal under specific conditions during its fabrication using a vertical boat process. It was thus found that a semi-insulating gallium arsenide single crystal with low dislocation is obtained regardless of a low support concentration. Therefore, a semi-insulating gallium arsenide single crystal substrate suitable for an optical device exhibiting high near-infrared transmittance and low dislocation capability, such as a VCSEL, was obtained, and the present disclosure is thus completed.

[0011] Next, aspects relating to the implementation of this revelation will be listed and described.

[0012] A semi-insulating gallium arsenide single-crystal substrate according to one aspect of the present disclosure is a semi-insulating gallium arsenide single-crystal substrate having a circular first principal surface. The diameter of the semi-insulating gallium arsenide single-crystal substrate is 95 mm or more and 205 mm or less. The light absorption coefficient of the semi-insulating gallium arsenide single-crystal substrate with respect to near-infrared light at a wavelength of 940 nm is 1.5 cm⁻¹. -1or less. The number of etch pits per square centimeter formed on the primary surface in an etching test by immersion of the semi-insulating gallium arsenide single-crystal substrate in molten potassium hydroxide at 500 °C for 10 minutes is 300 or less. The resistivity of the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C in a Hall test using the Van der Pauw method, is 1.0 × 10⁻⁶. 8Ω·cm or more. The semi-insulating gallium arsenide single-crystal substrate with such characteristics exhibits a sufficiently low light absorption coefficient with respect to near-infrared light and also a sufficiently low EPD, and can thus encompass both the property of high transmittance with respect to near-infrared light and the property of low dislocation capability. Therefore, the present disclosure can provide a semi-insulating gallium arsenide single-crystal substrate suitable for an optical device such as a VCSEL.

[0013] The light absorption coefficient is preferably determined by applying near-infrared light with a wavelength of 940 nm to the semi-insulating gallium arsenide single-crystal substrate at an angle of 85 degrees to measure the transmittance and reflectance of the near-infrared light of the semi-insulating gallium arsenide single-crystal substrate with an ultraviolet visible-infrared spectrophotometer, and assigning a numerical value of transmittance and a numerical value of reflectance as well as a numerical value of thickness of the semi-insulating gallium arsenide single-crystal substrate to the following equations 1, 2 and 3, and is preferably determined together with a reflectance in a reflection of the near-infrared light in the semi-insulating gallium arsenide single-crystal substrate. R+R(1−R)2exp(−2αd) / (1−r)=R* (1−R)2exp(−αd) / (1−r)=T* r=R2exp(2αd)

[0014] In equation 1, equation 2 and equation 3, R* represents the reflectance taking into account multiple reflections, measured with an ultraviolet-visible-infrared spectrophotometer, and the unit of reflectance is dimensionless.

[0015] T* represents the transmittance taking into account multiple reflections, measured with an ultraviolet-visible-infrared spectrophotometer, and the unit of transmittance is dimensionless.

[0016] α represents the light absorption coefficient, and the unit of the light absorption coefficient is cm. -1 .

[0017] R represents a reflectance value upon reflection of near-infrared light in the semi-insulating gallium arsenide single-crystal substrate, and one unit of reflectance upon reflection is dimensionless.

[0018] d represents a thickness of the semi-insulating gallium arsenide single crystal substrate, and one unit of thickness is cm.

[0019] Thus, a semi-insulating gallium arsenide single-crystal substrate can be provided that has a sufficiently low light absorption coefficient with respect to near-infrared light and high transmittance with respect to infrared light.

[0020] A carrier concentration in the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C in a Hall measurement according to the Van der Pauw method, is preferably 8.0 × 10 6 / cm 3 or less. The electron mobility of the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C in the Hall measurement according to the Van der Pauw method, is preferably 4500 cm⁻¹. 2 / V·s or more. Thus, it is possible to incorporate a higher transmittance with respect to near-infrared light.

[0021] An average value of residual stress, as an absolute value of the difference between a strain along a radial direction of the first main surface and a strain along a tangential direction of the first main surface, is preferably 5.0 × 10 -6 or less. Thus, a semi-insulating gallium arsenide single-crystal substrate can be provided that exhibits hardly any cracks in a manufacturing process.

[0022] An EL2 concentration of the semi-insulating gallium arsenide single-crystal substrate is preferably 7.5 × 10 15 cm -3 or more and 1.0 × 10 16 cm -3 or less. Thus, it is possible to incorporate a higher transmittance with respect to near-infrared light.

[0023] Preferably, the semi-insulating gallium arsenide single-crystal substrate contains carbon, and the atomic concentration of carbon in the semi-insulating gallium arsenide single-crystal substrate is 5.0 × 1015 cm -3 or more and 1.2 × 10 16 cm -3 or less. Thus, it is possible to incorporate a higher transmittance with respect to near-infrared light.

[0024] The semi-insulating gallium arsenide single-crystal substrate is preferably used in a vertical surface-emitting laser. This significantly improves the fabrication yield of an optical device such as a VCSEL. Here, "fabrication yield" refers not only to the required properties such as high near-infrared transmittance and low dislocation capability, but also to the efficiency with which a product with sufficient operational reliability and lifetime can be manufactured.

[0025] A substrate with an epitaxial layer according to one aspect of the present disclosure comprises the semi-insulating gallium arsenide single-crystal substrate and an epitaxial layer arranged on the first principal surface. The epitaxial layer includes an infrared emission layer. The substrate with the epitaxial layer, possessing such features, can provide a substrate with an epitaxial layer suitable for an optical device such as a VCSEL by exhibiting both the properties of high near-infrared transmittance and low dislocation capability inherent in the semi-insulating gallium arsenide single-crystal substrate.

[0026] A method for producing a semi-insulating gallium arsenide single crystal according to one aspect of the present disclosure is a method for producing a semi-insulating gallium arsenide single crystal using a vertical boat process, wherein the manufacturing process comprises preparing a device for growing a single crystal, comprising at least one cylindrical crucible and a heating element for heating the crucible, receiving a seed crystal at a lower section of the crucible and receiving gallium arsenide mass at an upper section compared to the seed crystal in the crucible, heating the crucible by the heating element to partially melt the gallium arsenide and the seed crystal, thereby not only obtaining a gallium arsenide melt but also bringing the gallium arsenide melt and a residue of the seed crystal into contact.and growing a crystal on the seed crystal in the gallium arsenide melt to obtain a semi-insulating gallium arsenide single crystal. Obtaining a semi-insulating gallium arsenide single crystal is carried out by satisfying a relationship between the following equations 4, 5, and 6. 0.20°C / mm≤X≤0.30°C / mm X+0.0012°C / mm2×Y≤Z1≤X+0.0024°C / mm2×Y 0.26°C / mm≤Z2≤0.42°C / mm

[0027] In Formula 4, Formula 5 and Formula 6, X represents a temperature gradient along an axial direction of the crucible, measured with a cross-sectional area between the crystal and the gallium arsenide melt as the center point, and is the unit of the temperature gradient °C / mm.

[0028] Y represents a distance from the interface to a first reference point in the crystal, and one unit of distance is mm.

[0029] Z1 represents a temperature gradient along an axial direction of the crucible, measured with the first reference point as the center point, and the unit of the temperature gradient is °C / mm.

[0030] Z2 represents a temperature gradient along an axial direction of the crucible, measured with the first reference point at a distance of 50 mm from the interface to the first reference point as its center point, and one unit of the temperature gradient is °C / mm.

[0031] According to the manufacturing process with these characteristics, it is possible to obtain a semi-insulating gallium arsenide single crystal substrate that includes both the properties of high transmittance for near-infrared light and low dislocation capability, and is therefore suitable for an optical device such as a VCSEL.

[0032] The apparatus for growing single crystals preferably comprises one or more thermocouples located outside the crucible in the radial direction. The thermocouple(s) is / are preferably movable in a direction parallel to the axial direction of the crucible. This improves the production yield. [Details of the implementation examples]

[0033] An embodiment according to the present disclosure (hereinafter also referred to as the "present embodiment") is described in more detail below, although the present disclosure is not limited to this embodiment. The following description is given with reference to the drawings, whereby identical or corresponding elements in the present description and the drawings are marked with the same symbols and identical or corresponding elements are not described again. In the drawings, the scale has been adjusted and shown accordingly for better understanding of the individual components, whereby the scale of the components shown in the drawings does not necessarily correspond to the scale of the actual components.

[0034] In the following, the designation "A to B" denotes the upper and lower limits of a range (i.e., A or more and B or less), and if the unit of A is not specified and only the unit of B is given, the units of A and B are identical. Where a compound or the like is represented herein by a chemical formula, and no atomic ratio is specifically restricted, every conventionally known atomic ratio is included, and there is no restriction to a stoichiometric range. For example, in the description "GaAs," the ratio of the number of atoms that make up GaAs is not restricted to Ga:As = 1:1, and every conventionally known atomic ratio is included.

[0035] The “first principal surface” of the semi-insulating gallium arsenide single-crystal substrate refers here to one of two circular principal surfaces of the substrate and specifically signifies a principal surface on which, for example, an infrared emission layer is to be deposited as an epitaxial layer in the case of the formation of a substrate with an epitaxial layer, as described below, from the semi-insulating gallium arsenide single-crystal substrate. In this context, the other principal surface, which is not the “first principal surface” of the two circular principal surfaces of the substrate, refers to the “second principal surface.” The term “semi-insulating” in the semi-insulating gallium arsenide single-crystal substrate described herein denotes the electrical properties of a gallium arsenide single-crystal substrate that exhibits high resistivity and a resistivity of 1.0 × 10⁻⁶ Ω·m. 7 Ω·cm or more.

[0036] When the diameter of the semi-insulating gallium arsenide single-crystal substrate is specified as "100 mm," this means that the diameter is approximately 100 mm (about 95 to 105 mm) or 4 inches. When the diameter is specified as "150 mm," this means a diameter of approximately 150 mm (about 145 to 155 mm) or 6 inches. When the diameter is specified as "200 mm," this means a diameter of approximately 200 mm (about 195 to 205 mm) or 8 inches. The diameter of the semi-insulating gallium arsenide single-crystal substrate can be measured using a conventional external measuring instrument, such as a caliper.

[0037] The semi-insulating gallium arsenide single-crystal substrate has a "circular" first principal surface. The "circular" shape expressed here by the shape of the first principal surface includes not only a geometric circle but also a shape in which, due to the formation of at least one indentation, orientation surface (hereinafter also referred to as "OF"), or index surface (hereinafter also referred to as "IF"), a geometric circle is not formed by the first principal surface. In other words, the "shape in the case of the first principal surface not forming a geometric circle" means a shape in the case of a shortened length of a line segment extending from any point on the indentation, OF, and IF to the center of the first principal surface, among line segments extending from any point on an outer circumference of the first principal surface to the center of the first principal surface.This means that the first principal surface is assumed to have a shape that is a "circular shape" based on a shape prior to the formation of the notch, OF, IF, and the like. Therefore, the center of the first principal surface and the diameter of the semi-insulating gallium arsenide single-crystal substrate are to be determined as position and size (length) based on a circular shape prior to the formation of the notch, OF, IF, and the like. The "shape in the case of the first principal surface not forming a geometric circular shape" here also includes a shape in which the lengths of all line segments extending from any point on an outer circumference of the first principal surface to the center of the first principal surface are not necessarily identical due to the shape of a semi-insulating gallium arsenide single crystal prior to the cutting of the single crystal into a semi-insulating gallium arsenide single-crystal substrate.In this case, the center of the first principal surface refers to a position of the center of gravity, and the diameter of the semi-insulating gallium arsenide single-crystal substrate refers to the length of the longest line segment among the line segments that each extend from any point on an outer circumference of the semi-insulating gallium arsenide single-crystal substrate through the center of the first principal surface to another point on the outer circumference.

[0038] In crystallographic descriptions, an individual orientation is denoted by [], a collective orientation by <>, an individual plane by (), and a collective plane by {}. A negative crystallographic index, normally expressed as a superscript number with a hyphen (-), is indicated here by a minus sign before the number. [Semi-insulating gallium arsenide single crystal substrate]

[0039] A semi-insulating gallium arsenide single-crystal substrate according to the present embodiment (hereinafter also referred to as a "semi-insulating GaAs single-crystal substrate") is a semi-insulating GaAs single-crystal substrate with a circular first principal face. The diameter of the semi-insulating GaAs single-crystal substrate is 95 mm or more and 205 mm or less. The light absorption coefficient of the semi-insulating GaAs single-crystal substrate with respect to near-infrared light at a wavelength of 940 nm is 1.5 cm⁻¹. -1or less. The number of etch pits per square centimeter formed on the primary surface in an etching test by immersing the semi-insulating GaAs single-crystal substrate in molten potassium hydroxide at 500 °C for 10 minutes is 300 or less. Furthermore, the resistivity of the semi-insulating GaAs single-crystal substrate, measured at 25 °C in a Hall test using the Van der Pauw method, is 1.0 × 10⁻⁶. 8Ω·cm or more. The semi-insulating GaAs single-crystal substrate with such characteristics exhibits a sufficiently low light absorption coefficient with respect to near-infrared light and also a sufficiently low EPD, and can thus possess both the property of high transmittance with respect to near-infrared light and the property of low dislocation capability. Therefore, the present embodiment can provide a semi-insulating GaAs single-crystal substrate suitable for an optical device such as a VCSEL.

[0040] The reason why the semi-insulating GaAs single-crystal substrate according to the present embodiment can exhibit both high near-infrared transmittance and low dislocation capability is due to the following characteristics. The reason why a semi-insulating GaAs single-crystal substrate with high resistivity has traditionally been used as a material for optical devices such as VCSELs is that, for example, a semi-insulating GaAs single-crystal substrate with a low support concentration generally has a low absorption coefficient with respect to near-infrared light and therefore high near-infrared transmittance. However, a semi-insulating GaAs single-crystal substrate with a low support concentration often exhibits a high EPD (expansion potential difference) because many dislocations are present in a single crystal.When such a semi-insulating GaAs single-crystal substrate is used in an optical device such as a VCSEL, the problem is that poor yield and a lack of operational reliability or a short lifetime occur.

[0041] A method for introducing a metal atom such as silicon as an impurity (doper) into such a semi-insulating GaAs single-crystal substrate is known to reduce the substrate's EPD. However, such a semi-insulating GaAs single-crystal substrate tends to have a reduced resistivity due to the introduction of this impurity and can therefore be difficult to use in optical devices. Furthermore, if the carrier concentration is higher due to the introduction of such an impurity, the absorption coefficient with respect to near-infrared light tends to be greater.While it is assumed that two different impurities are introduced to reduce the EPD and the carrier concentration, thereby enabling such a semi-insulating GaAs single-crystal substrate to exhibit a lower absorption coefficient, this leads to an extreme reduction in electron mobility and thus the risk of making its application in an optical device difficult. In other words, while desirable, it was technically challenging to obtain a semi-insulating GaAs single-crystal substrate that possesses properties such as a sufficiently low light absorption coefficient with respect to near-infrared light and EPD, as well as high stability, and is therefore suitable for an optical device.

[0042] The inventors focused on reducing the EPD in a semi-insulating GaAs single-crystal substrate exhibiting a low support concentration and a low absorption coefficient with respect to near-infrared light, in order to achieve high near-infrared transmittance without resorting to the introduction of an impurity. Specifically, a semi-insulating gallium arsenide single crystal (hereinafter also referred to as a "semi-insulating GaAs single crystal") was fabricated in which the occurrence of dislocations was suppressed as much as possible by critically controlling the growth temperature of the semi-insulating GaAs single crystal during its fabrication using a vertical boat process.In particular, critical control was implemented to ensure that not only the temperature of an interface between a solidified semi-insulating GaAs single crystal and a gallium arsenide melt in contact with this semi-insulating GaAs single crystal, but also the temperature within the solidified semi-insulating GaAs single crystal itself, corresponds to a temperature gradient derived from a predetermined equation. It was thus designed that a semi-insulating GaAs single crystal with low dislocation (in particular, an EPD of 300 cm⁻¹) -2or less) is obtained regardless of a low carrier concentration. It follows from the above that a semi-insulating GaAs single-crystal substrate according to the present embodiment can exhibit a sufficiently low light absorption coefficient with respect to near-infrared light and a sufficiently low EPD, and can therefore possess both the property of high transmittance with respect to near-infrared light and the property of low dislocation capability. <Erste Hauptoberfläche>

[0043] The semi-insulating GaAs single-crystal substrate has a circular primary surface. As described above, the primary surface is one of two circular primary surfaces of the substrate, onto which, for example, an infrared emission layer is to be deposited as an epitaxial layer when forming a substrate with an epitaxial layer. The primary surface is preferably a mirror surface with a surface roughness, represented by the arithmetic mean roughness (Ra), of 1 nm or less, as described below. <durchmesser>

[0044] The diameter of the semi-insulating GaAs single-crystal substrate is 95 mm or more and 205 mm or less. The semi-insulating GaAs single-crystal substrate with a diameter of 95 mm or more and 205 mm or less preferably refers to one with a diameter of specifically 100 mm, 150 mm, or 200 mm, i.e., a diameter of 4 inches, 6 inches, or 8 inches, respectively. Thus, a large-diameter semi-insulating GaAs single-crystal substrate with a diameter of 95 mm or more and 205 mm or less can possess both the property of high near-infrared transmittance and the property of low dislocation capability. As described above, the diameter of the semi-insulating GaAs single-crystal substrate can be measured using a conventionally known external measuring instrument, such as a caliper. < Any property of the light absorption coefficient, the EPD, the resistivity, and the like >

[0045] In the present embodiment, the light absorption coefficient of the semi-insulating GaAs single-crystal substrate with respect to near-infrared light at a wavelength of 940 nm is 1.5 cm⁻¹. -1 or less. The number of etch pits per square centimeter formed on the primary surface in an etching test involving immersion of the semi-insulating GaAs single-crystal substrate in molten potassium hydroxide at 500 °C for 10 minutes is 300 or less. Furthermore, the resistivity of the semi-insulating GaAs single-crystal substrate, measured at 25 °C in a Van der Pauw Hall test, is 1.0 × 10⁻⁶. 8 Ω·cm or more.

[0046] The following describes the individual properties of the light absorption coefficient with respect to near-infrared light at a wavelength of 940 nm, the EPD-specific resistivity, and the like, measured in the semi-insulating GaAs single-crystal substrate, with reference to Fig. 1 to Fig. 3 described. Fig. Figure 1 is an illustrative diagram describing a measurement location (measuring area) for measuring each property of the light absorption coefficient and EL2 concentration of a semi-insulating gallium arsenide single crystal substrate according to the present embodiment. Fig. Figure 2 is an illustrative diagram that describes a measuring point (measuring range) for measuring the dislocation density of a semi-insulating gallium arsenide single crystal substrate according to the present embodiment. Fig. Figure 3 is an illustrative diagram describing a pattern for a Hall measurement, wherein the pattern is prepared with a central section of a semi-insulating gallium arsenide single-crystal substrate according to the present embodiment to measure each property of the resistivity, carrier concentration and electron mobility of the semi-insulating gallium arsenide single-crystal substrate. (Light absorption coefficient)

[0047] In the present embodiment, the light absorption coefficient of the semi-insulating GaAs single-crystal substrate with respect to near-infrared light at a wavelength of 940 nm is 1.5 cm⁻¹. -1 or less. In particular, the light absorption coefficient with respect to near-infrared light at a wavelength of 940 nm, determined with the center of the semi-insulating GaAs single-crystal substrate as the measurement object, has a value of 1.5 cm. -1 or less. The light absorption coefficient is preferably 1.3 cm. -1 or less, preferably 1.25 cm -1 or less, and most preferred less than 1.25 cm -1 Thus, it is possible to achieve sufficient transmittance for near-infrared light. If the light absorption coefficient is greater than 1.5 cm -1 The semi-insulating GaAs single-crystal substrate tends to absorb near-infrared light more strongly, making it difficult to achieve sufficient near-infrared transmittance. A smaller numerical value for the light absorption coefficient improves transmittance, so the lower limit does not need to be restricted, but the light absorption coefficient is typically 0.01 cm⁻¹. -1 or more.

[0048] The light absorption coefficient can be determined by a conventional method from the transmittance and reflectance of a substance, measured with an ultraviolet-visible-infrared spectrophotometer or the like. When the transmittance and reflectance of light of the semi-insulating GaAs single-crystal substrate are measured with an ultraviolet-visible-infrared spectrophotometer or the like, the occurrence of multiple reflections between two parallel principal surfaces must be taken into account, and therefore the light absorption coefficient is preferably determined by the following method.In particular, the light absorption coefficient is preferably determined by applying near-infrared light with a wavelength of 940 nm to the semi-insulating GaAs single-crystal substrate at an angle of 85 degrees, measuring the transmittance and reflectance of the near-infrared light of the semi-insulating GaAs single-crystal substrate with an ultraviolet-viewing infrared spectrophotometer, and assigning the numerical value of the transmittance, the numerical value of the reflectance, and the numerical value of the thickness of the semi-insulating GaAs single-crystal substrate to Equation 1, Equation 2, and Equation 3, and preferably determining together with a reflectance in a reflection of the near-infrared light in the semi-insulating GaAs single-crystal substrate. R+R(1−R)2exp(−2αd) / (1−r)=R* (1−R)2exp(−αd) / (1−r)=T* r=R2exp(2αd) In equation 1, equation 2 and equation 3, R* represents the reflectance taking into account multiple reflections, measured with the ultraviolet-visible-infrared spectrophotometer, and the unit of reflectance is dimensionless. T* represents the transmittance taking into account multiple reflections, measured with an ultraviolet-visible-infrared spectrophotometer, and the unit of transmittance is dimensionless. α represents the light absorption coefficient, and the unit of the light absorption coefficient is cm. -1 . R represents the reflectance in a reflection of near-infrared light in the semi-insulating GaAs single-crystal substrate, and the unit of reflectance in a reflection is dimensionless. d represents the thickness of the semi-insulating GaAs single-crystal substrate, and the unit of thickness is cm.

[0049] The following describes a method for determining the light absorption coefficient with reference to Fig. 1. In detail, a semi-insulating GaAs single-crystal substrate 1, serving as the measurement object, is first obtained by applying a conventionally known processing method to a semi-insulating GaAs single crystal obtained based on a fabrication process described below. From this single semi-insulating GaAs single-crystal substrate 1, a rectangular section 11a (for example, 600 mm thick) with dimensions of 20 mm length × 20 mm width is produced, with its center point (for example, the center point of a first primary surface 11) as the center point O, thus obtaining a measurement sample of the light absorption coefficient.Next, near-infrared light with a wavelength of 940 nm is directed at an angle of 85 degrees, inclined by 5 degrees from the perpendicular direction of incidence to the main surface, onto the center of rectangular section 11a using an ultraviolet-visible-infrared spectrophotometer (trade name (article number): “U-4000”, manufactured by Hitachi High-Tech Corporation) and an attached unit for measuring absolute reflectance. In this way, the transmittance and reflectance of the near-infrared light through the semi-insulating GaAs single-crystal substrate 1 are measured. The transmittance and reflectance are obtained as measurements by multiple reflections between two parallel main surfaces (namely, the front and back) of the semi-insulating GaAs single-crystal substrate 1.Finally, the light absorption coefficient can be determined by assigning the transmittance and reflectance, as well as the thickness of the rectangular section, to equations 1, 2, and 3, taking multiple reflections into account, and performing repeated numerical calculations. Here, the light absorption coefficient, along with the reflectance at a single reflection, is determined at the first principal surface 11 of the semi-insulating GaAs single-crystal substrate 1. The "reflectance at a single reflection" refers to a reflectance determined based on the transmission and reflection of incident near-infrared light that first appears at the first principal surface 11 of the semi-insulating GaAs single-crystal substrate 1.The light absorption coefficient obtained from the aforementioned rectangular section, which was selected as the measurement object, is defined here as the light absorption coefficient of the semi-insulating GaAs single-crystal substrate with respect to near-infrared light at a wavelength of 940 nm. Equations 1 and 2, taking multiple reflections into account, are used to determine the convergence value of infinite geometric series, assuming that infinite reflections are received. (EPD)

[0050] The number of etch pits per square centimeter formed on the first main surface in an etch test by immersing the semi-insulating GaAs single-crystal substrate in molten potassium hydroxide at 500 °C for 10 minutes is 300 or less. In other words, the dislocation density (EPD; etch pit density) of the first main surface of the semi-insulating GaAs single-crystal substrate is 300 cm³. -2 or less. The EPD is preferably 260 cm². -2 or less, and preferably 200 cm -2 or less. Thus, the semi-insulating GaAs single-crystal substrate can exhibit a low dislocation capability. In a case where the EPD of the first major surface of the semi-insulating GaAs single-crystal substrate is more than 300 cm² -2 If the EPD is high, the defect due to dislocation in the semi-insulating GaAs single-crystal substrate increases, which can negatively impact the fabrication yield when used in VCSEL. A lower numerical value for the EPD is desirable, so that the lower limit does not need to be restricted, but the EPD is typically 0.5 cm. -2 or more.

[0051] The following describes the procedure for measuring the EPD with reference to Fig. 2. First, for example, a semi-insulating GaAs single-crystal substrate 1 is obtained as a test object using a fabrication process described below. Furthermore, a main surface (e.g., the first main surface 11) of the semi-insulating GaAs single-crystal substrate 1 is polished to a mirror finish and then immersed for 10 minutes in a potassium hydroxide (KOH) melt at 500 °C to form a corroded pore, a so-called etch pit, on the first main surface 11. To clear the etch pit, the first main surface 11, which is polished to a mirror finish, can be pretreated for at least 10 minutes with sulfuric acid and hydrogen peroxide or with an aqueous ammonia solution and hydrogen peroxide before immersion in a potassium hydroxide (KOH) melt.Although the etching pit does not have the same meaning as a dislocation from an academic point of view, it can be considered the equivalent of a dislocation in engineering.

[0052] Next, a grid 11b, in which 5 mm squares are arranged so that they do not overlap but are as close to a straight line as possible, is formed on the entire surface of the first primary surface 11 of the semi-insulating GaAs single-crystal substrate 1 removed from the potassium hydroxide melt, and the first primary surface 11 is fractionated with this grid 11b. The grid 11b can, for example, be written directly onto the substrate and thus formed using a pen or the like. Subsequently, each square formed by the grid 11b on the first primary surface 11 is defined as a field of view, and the number of etch pits present in each field of view is counted using a known optical microscope (for example, trade name: “ECLIPSE (registered trademark) LV150N”, manufactured by Nikon Corporation). Finally, the number of etch pits present in each field of view is converted into the number per square centimeter.This yields the number of etch pits per square centimeter in terms of the number of squares comprising the lattice 11b. A value obtained by dividing the sum of these etch pits per square centimeter by the number of squares can then be determined as the EPD of the first principal surface 11. In a case where an outer perimeter of the first principal surface and an outer surface thereof appear in the field of view as described above, the field of view is excluded from the object for the EPD calculation. This is because a region near the outer perimeter of a semi-insulating GaAs single-crystal substrate 1 exhibits a highly variable number of etch pits depending on the substrate and is not typically used as material for an optical device. (Specific resistance)

[0053] In the present embodiment, the specific resistance of the semi-insulating GaAs single-crystal substrate, measured at 25 °C in a Hall measurement according to the Van der Pauw method, is 1.0 × 10 8 Ω·cm or more. In particular, the resistivity determined at 25 °C in a Hall measurement using the Van der Pauw method with the center of the semi-insulating GaAs single-crystal substrate as the test object, has a value of 1.0 × 10 8 Ω·cm or more. The resistivity is preferably 1.5 × 10⁻⁶. 8 Ω·cm or more, preferably 2.0 × 10 8 Ω·cm or more. This makes it possible to achieve sufficient transmittance for near-infrared light. If the resistivity is less than 1.0 × 10 8 Ω·cm is the case for the semi-insulating GaAs single-crystal substrate, where the above light absorption coefficient tends to be greater than 1.5 cm -1 The danger lies in the difficulty of achieving sufficient transmittance for near-infrared light. A higher numerical value of resistivity tends to improve the transmittance of the semi-insulating GaAs single-crystal substrate, so the upper limit does not need to be restricted, but the resistivity is typically 3.0 × 10⁻⁶. 8 Ω·cm or less.

[0054] The following describes the procedure for determining the specific resistance with reference to Fig. 1 and Fig. 3 described in more detail. First, as for example in Fig. Figure 1 illustrates how a semi-insulating GaAs single-crystal substrate 1, serving as the measurement object, is obtained by applying a conventionally known processing method to a semi-insulating GaAs single crystal obtained based on a fabrication process described below. A rectangular section 11a (e.g., 600 mm thick) measuring 4 mm in length × 4 mm in width, whose center point (e.g., the center point of the first principal surface 11) serves as the center point O, is fabricated from a central section of this single semi-insulating GaAs single-crystal substrate 1. Subsequently, as shown in Figure 1, the substrate is processed as follows: Fig. As illustrated in Figure 3, an electrode 21 is formed at each of the four corners of the rectangular section 11a (area to be measured). This electrode 21 comprises an alloy containing gold, nickel, and germanium, thus providing a sample for the Hall measurement. The shape of the electrode 21 is not limited to the rectangular shape shown but can also be fan-shaped or circular. The Hall measurement according to the Van der Pauw method can be performed on the rectangular section 11a, which comprises the electrode 21, at an ambient temperature of 25 °C to determine the resistivity. The resistivity determined based on the aforementioned rectangular section, which was selected as the sample, is defined here as the resistivity of the semi-insulating GaAs single-crystal substrate, measured at 25 °C in a Hall measurement according to the Van der Pauw method. (Carrier concentration and electron mobility)

[0055] In the present embodiment, the carrier concentration in the semi-insulating GaAs single-crystal substrate, measured at 25 °C in a Hall measurement according to the Van der Pauw method, is preferably 8.0 × 10 6 cm -3 or less. The electron mobility of the semi-insulating GaAs single-crystal substrate, measured at 25 °C in a Hall measurement according to the Van der Pauw method, is preferably 4500 cm⁻¹. 2 / V·s or more. This makes it possible to incorporate a higher transmittance for near-infrared light. If the carrier concentration is 8.0 × 10 6 cm -3 or less and the electron mobility 4500 cm 2 If the light absorption coefficient of the semi-insulating GaAs single-crystal substrate is greater than / V·s or more, it will not exceed 1.5 cm. -1 , which can improve the transmittance for near-infrared light.

[0056] The carrier concentration is preferably 3.0 × 10 6 cm -3 or more and 7.0 × 10 6 cm -3 or less. The electron mobility is preferably 5000 cm⁻¹. 2 / V·s or more and 8000 cm 2 / V·s or less. Both the carrier concentration and the electron mobility can be determined using the same method as the method described above for measuring the resistivity. (Residual voltage)

[0057] The average value of the residual stress, as an absolute value of the difference between the stress along the radial direction of the first main surface and the stress along the tangential direction of the first main surface in the semi-insulating GaAs single-crystal substrate, is preferably 5.0 × 10 -6 or less. Thus, a semi-insulating GaAs single-crystal substrate can be provided that exhibits virtually no cracking in a single manufacturing process. The average residual stress is preferably 3.5 × 10⁻⁶. -6 or less, preferably 1.0 × 10 -6 or less. The average residual stress is preferably 5.0 × 10 -6 or less, since the semi-insulating GaAs single-crystal substrate is sufficiently protected against cracking in a fabrication process and has no adverse effects on the yield. The lower limit of the average residual stress value is not particularly limited, but the average residual stress value is actually 5.0 × 10 -7 or more. Here, the stress along the radial direction of the first main surface can be represented by "Sr" and the stress along the tangential direction of the first main surface by "St".

[0058] The average residual stress value can have a preferred value, based, for example, on the difference in the diameter of the semi-insulating GaAs single-crystal substrate, and the like. For example, in a case where the diameter of the substrate is 100 mm, the average residual stress value is preferably 2.0 × 10 -6 or less, in a case where the diameter of the substrate is 150 mm, the average value of the residual stress is preferably 3.5 × 10 -6 or less, and in a case where the diameter of the substrate is 200 mm, the average value of the residual stress is preferably 5.0 × 10 -6 or less. The semi-insulating GaAs single-crystal substrate may also exhibit a preferred average residual strain value depending on the type of atom present as an impurity.

[0059] The residual stress (hereinafter also referred to as "|Sr-St|") as the absolute value of the difference between the stress along the radial direction of the first principal surface and the stress along the tangential direction of the first principal surface can be measured using a photoelastic method described in "Review of Scientific Instruments Vol. 64 No. 7, pp. 1815-1821 (1993)". First, the semi-insulating GaAs single-crystal substrate (for example, with a thickness of 700 mm) is subjected to mirror polishing of the first principal surface and a second principal surface opposite the first principal surface, as in the above procedure for measuring the EPD. Thus, the first principal surface and the second principal surface are each considered polished surfaces with an arithmetic mean roughness Ra of 0.1 nm or more and 0.5 nm or less, respectively.Next, the photoelastic method, in which light is transferred from one main surface to an opposite main surface, can be applied to measure the residual stress using the entire surface of the substrate as the object. Specifically, the residual stress can be determined as an absolute value |Sr-St| in the photoelastic method. The residual stress (|Sr-St|) is defined in the photoelastic method by the following equation (1). [Equation 1] |Sr−St|=kδ[(cos2φP11−P12)2+(sin2φP44)2]1 / 2

[0060] In equation (1), k = (λ / πdn0 3 ).

[0061] In equation (1) λ represents the wavelength (µm) of the light used for measurement, d the thickness (µm) of the semi-insulating GaAs single-crystal substrate used for measurement, n0 the refractive index of a stress-free crystal, δ the phase difference resulting from the birefringence of a sample to be measured, φ the azimuth of the principal vibration, and P 11 , P 12 and P 44 each a photoelastic constant.

[0062] The residual stress (|Sr-St|) on the first principal surface of the semi-insulating GaAs single-crystal substrate can be determined using the photoelastic method by measuring only the phase difference δ and the azimuth of the principal vibration φ, which arise due to the birefringence of the sample. For example, the average value of the residual stress (|Sr-St|) can be determined using the following method if the first principal surface of the semi-insulating GaAs single-crystal substrate (675 µm thick) is the (100) plane of a GaAs single crystal. First, a semiconductor laser with a wavelength of 1300 nm is used as the light source. Furthermore, the semiconductor laser is directed perpendicularly onto the first principal surface to illuminate the entire surface as an object at intervals of 0.5 mm in each of the mutually perpendicular directions. <011> and to sample <01-1>, thereby measuring the phase difference δ and the azimuth of the main oscillation φ.The spot size of the semiconductor laser is set to a diameter of 0.5 mm or less. This allows the residual stress to be determined using the photoelastic method described above, within an area subdivided into 0.5 mm × 0.5 mm sections per measurement point. Finally, the sum of the resulting residual stress measurements can be divided by the total number of measurement areas to determine the average residual stress (|Sr-St|). Any section of the substrate's outer circumference that undergoes grinding or similar processes, preventing the semiconductor laser from being perpendicular to the primary surface, is excluded from the measurement for determining the average residual stress (|Sr-St|).Even in a case where an angular offset is provided on the first principal surface, the phase difference δ and the azimuth of the principal vibration φ are measured by the semiconductor laser incident perpendicularly on the first principal surface and scanning in a direction in which each vector is projected perpendicular to the (011) plane and the (01-1) plane of a GaAs single crystal onto the first principal surface.

[0063] A distribution of the residual stress (|Sr-St|) on the first main surface can be represented, for example, by a diagram in Fig. 4 are shown. Fig. Figure 4 is a diagram describing a residual stress distribution on a first main surface of a semi-insulating gallium arsenide single-crystal substrate according to the present embodiment. Fig. Figure 4 shows that the vertical axis represents the magnitude of the residual stress and the horizontal axis the distance from the substrate center. For example, according to the figure in Fig. Figure 4 illustrated semi-insulating GaAs single-crystal substrates; the average residual stress was approximately 0.8 × 10 -6 , and there is no significant difference between the magnitude of residual stress at an outer circumference of the substrate and the magnitude of residual stress around the center of the substrate, and it is evident that the residual stress is suppressed at the same level over the entire area of ​​the substrate. (EL2 concentration)

[0064] The EL2 concentration of the semi-insulating GaAs single-crystal substrate is preferably 7.5 × 10 15 cm -3 or more and 1.0 × 10 16 cm -3 or less. In particular, the EL2 concentration, determined using the center of the semi-insulating GaAs single-crystal substrate as the measurement object, should preferably have a value of 7.5 × 10 15 cm -3 or more and 1.0 × 10 16 cm -3 or less. Thus, the carrier concentration of the semi-insulating GaAs single-crystal substrate can be sufficiently low, and therefore it is possible to incorporate a higher transmittance with respect to near-infrared light. The EL2 concentration is preferably 7.5 × 10 15 cm -3 or more and 9.5 × 10 15 cm -3 or less. If the EL2 concentration is 1.0 × 10 16 cm -3 or less, the possibility is that the above light absorption coefficient of the semi-insulating GaAs single-crystal substrate is 1.5 cm -1 The EL2 concentration exceeds this value by a very small amount, and thus it is easy to achieve sufficient transmittance with respect to near-infrared light. A lower numerical value of the EL2 concentration tends to improve the transmittance of the semi-insulating GaAs single-crystal substrate, so the lower limit does not need to be restricted, but the EL2 concentration should preferably be set to 7.5 × 10⁻⁶, taking into account the possibility of adverse effects on other properties and the like. 15 cm -3 or more.

[0065] The EL2 concentration can be determined using the following procedure.

[0066] In other words, the EL2 concentration can be determined by a known calculation method based on the value of the light absorption coefficient after determining the light absorption coefficient in the same way as in the above procedure for determining the light absorption coefficient, except that near-infrared light with a wavelength of 1100 nm at an angle of 85 degrees to the center of the rectangular section is used with an ultraviolet visible infrared spectrophotometer (trade name (part number): "V-570", manufactured by JASCO Corporation). A specific calculation method can be found, for example, in Fig. 3 of “Applied Physics Letters, Vol. 39, p. 747 (1981)”. The EL2 concentration, determined on the basis of the aforementioned rectangular section designated as the measurement object, is here defined as the EL2 concentration of the semi-insulating GaAs single-crystal substrate. (Average atomic carbon concentration)

[0067] The semi-insulating GaAs single-crystal substrate preferably comprises carbon. In this case, the average atomic concentration of carbon in the semi-insulating GaAs single-crystal substrate is preferably 5.0 × 10⁻⁶. 15 cm -3 or more and 1.2 × 10 16 cm -3 or less. In particular, the average atomic concentration of carbon, determined with the center of the semi-insulating GaAs single-crystal substrate as the measurement object, preferably has a value of 5.0 × 10 15 cm -3 or more and 1.2 × 10 16 cm -3 or less. Thus, the above EL2 concentration compensates for the carbon atom as an acceptor, and therefore the semi-insulating GaAs single-crystal substrate can exhibit higher resistivity and thus higher transmittance with respect to near-infrared light. The average atomic concentration of carbon is preferably 6.0 × 10 15 cm -3 or more and 1.0 × 10 16 cm -3 or less, and even more preferred 7.0 × 10 15 cm -3 or more and 9.0 × 10 15 cm -3 or less. If the average atomic concentration of carbon is 5.0 × 10 15 cm -3 or more, the probability that the above-mentioned light absorption coefficient of the semi-insulating GaAs single-crystal substrate is 1.5 cm -1 The difference is extremely small, so sufficient transmittance for near-infrared light can easily be achieved. A higher numerical value of the average atomic concentration of carbon tends to improve the transmittance of the semi-insulating GaAs single-crystal substrate, so the upper limit does not need to be restricted, but the average atomic concentration of carbon, taking into account the possibility of adverse effects on other properties and the like, should preferably be 1.2 × 10 16 cm -3 or less.

[0068] The average atomic concentration of carbon can be determined by the following procedure. First, a semi-insulating GaAs single-crystal substrate, serving as the sample, is obtained by applying a conventionally known processing method to a semi-insulating GaAs single crystal obtained based on a fabrication procedure described below. A strip section (e.g., 675 µm thick) measuring 10 mm in length × 1 mm in width, encompassing the center (e.g., center of the first main surface) of this single semi-insulating GaAs single-crystal substrate, is prepared to obtain a sample of the atomic concentration of carbon. Next, the intensity of the transmitted light I is measured at approximately 579.7 cm⁻¹. -1 The absorbance of the sample is measured using a Fourier transform infrared spectrometer (trade name (article number): "TENSOR II FTIR Spectrometer", manufactured by Bruker). The absorbance A = Log (I0 / I) is calculated as the logarithmic relationship between the absorbance and the intensity of the incident light I0. For this purpose, a control sample, in which the average atomic concentration (hereinafter also referred to as "C concentration") of carbon has been determined beforehand, is measured with the Fourier transform infrared spectrometer, thus generating a calibration curve. Finally, the C concentration of the sample can be determined from the absorbance A with reference to the calibration curve. Since the absorbance is approximately 579.7 cm⁻¹ -1 The absorption, which is due to lattice vibrations of carbon (C) substituting an As site, is calculated, with respect to the Fourier transform infrared spectrometer, as a value proportional to the C concentration. The atomic concentration of carbon, obtained based on the strip section defined above as the sample, is defined here as the average atomic concentration of carbon in the semi-insulating GaAs single-crystal substrate. In a case where the C concentration is so low that the absorption is lower, the C concentration can also be determined from a calibration curve corresponding to a much thicker sample. (Arithmetic mean of roughness Ra)

[0069] The arithmetic mean roughness Ra of the first principal surface in the semi-insulating GaAs single-crystal substrate is preferably 1 nm or less. In other words, the surface roughness of the first principal surface preferably has a value of 1 nm or less with respect to the arithmetic mean roughness Ra specified in JIS B 0601-2001. This improves the reflectivity of the first principal surface, making it advantageous for use in an optical device such as a VCSEL. The arithmetic mean roughness Ra of the first principal surface of the semi-insulating GaAs single-crystal substrate is preferably 0.5 nm or less, and more preferably 0.3 nm or less. Furthermore, a smaller numerical value of the arithmetic mean roughness Ra is advantageous so that the lower limit does not need to be restricted, with the arithmetic mean roughness Ra actually being 0.05 nm or more.

[0070] The arithmetic mean roughness Ra of the first main surface can be measured in a periodic contact mode using an atomic force microscope (for example, trade name: “Dimension Edge”, manufactured by Bruker). < Contamination (Doping)>

[0071] An impurity atom can be introduced into the semi-insulating GaAs single-crystal substrate to adjust properties such as the semi-insulation, provided that the effects of the present disclosure are not adversely affected. Examples of a donor dopant that can be added to adjust the semi-insulating properties may include Si atoms (silicon) and Te atoms (tellurium), and may include a Zn atom (zinc) in addition to the C (carbon) dopant described above. <off-angle>

[0072] The first principal surface of the semi-insulating GaAs single-crystal substrate is preferably the {100} plane without an offset angle or a plane with an offset angle of more than 0° and less than 3° relative to the {100} plane of a semi-insulating GaAs single crystal. In a case where the first principal surface has an offset angle of more than 0° and 3° or less from the {100} plane of a semi-insulating GaAs single crystal, infrared emission at, for example, 940 nm can be achieved from a strain quantum wave layer of a substrate with an epitaxial layer in which an x Ga 1-x The As layer (0 ≤ x < 1) is arranged as an infrared emission layer on the first main surface.

[0073] A semi-insulating GaAs single-crystal substrate, in which the first principal surface is the {100} plane of a semi-insulating GaAs single crystal, can be obtained by cutting the {100} plane, which has no offset angle, as the first principal surface from a semi-insulating GaAs single crystal serving as raw material. Alternatively, a semi-insulating GaAs single-crystal substrate, in which the first principal surface is the plane having an offset angle of more than 0° and 3° or less from the {100} plane of a semi-insulating GaAs single crystal, can be obtained by performing a conventionally known inclined slice cutting procedure on a semi-insulating GaAs single crystal serving as raw material, such that the plane having an offset angle of more than 0° and 3° or less from the {100} plane serves as the first principal surface.In a case where such a raw material is obtained, a growth direction of the semi-insulating GaAs single crystal is preferably the <100> -direction. In the present disclosure, the “offset angle” has an accuracy error of ± 0.5°. For example, if the first principal surface is the {100} plane, the first principal surface can have an offset angle of -0.5° to 0.5° with respect to the {100} plane. For example, if the first principal surface is the plane with an offset angle of 3° with respect to the {100} plane, the first principal surface can have an offset angle of 2.5° to 3.5° with respect to the {100} plane.

[0074] The offset angle from the {100} plane in the first main surface of the semi-insulating GaAs single crystal substrate can be measured using a conventionally known crystal orientation measuring device (for example, trade name (article number): “2991G2”, manufactured by Rigaku Corporation). <anwendung>

[0075] A semi-insulating GaAs single-crystal substrate according to the present embodiment is preferably used in a vertical surface-emitting laser (VCSEL). Thus, properties inherent in the semi-insulating GaAs single-crystal substrate, including high near-infrared transmittance and low dislocation capability, can be utilized in a VCSEL, and therefore a VCSEL with a significantly improved fabrication yield can be provided. [Substrate with epitaxial layer]

[0076] A substrate with an epitaxial layer according to the present embodiment comprises the semi-insulating GaAs single-crystal substrate and an epitaxial layer arranged on the first primary surface. The epitaxial layer includes an infrared emission layer. The substrate with an epitaxial layer possessing such features can provide a substrate with an epitaxial layer suitable for an optical device such as a VCSEL by exhibiting both the properties of high near-infrared transmittance and low dislocation capability inherent in the semi-insulating GaAs single-crystal substrate. <epitaxieschicht>(Infrared emission layer)

[0077] The substrate with an epitaxial layer comprises an epitaxial layer arranged on the first primary surface of the semi-insulating GaAs single-crystal substrate, as described above. The epitaxial layer includes an infrared emission layer. In this case, the infrared emission layer can be arranged directly on the first primary surface or on the first primary surface with, for example, an n-type or p-type blotter layer or a Bragg reflector (DBR layer; DBR = Distributed Bragg Reflector) interposed.

[0078] The infrared emission layer can be a compound layer formed by epitaxial growth on the first major surface of the semi-insulating GaAs single-crystal substrate or the DBR layer. The composition of the compound layer need not be particularly restricted, as long as, for example, epitaxial growth on the first major surface or the DBR layer is possible, and a layer comprising a compound semiconductor single crystal is preferred from the standpoint of growing a high-quality compound layer. Examples of a layer comprising a compound semiconductor single crystal may include a composition comprising a group 13 element such as Al (aluminum), Ga (gallium), or In (indium) and a group 15 element such as N (nitrogen), P (phosphorus), or As (arsenic). A specific example includes an In x Ga 1-x As layer (0 ≤ x < 1), an In x Ga 1-x As y P 1-y -layer (0 ≤ x < 1, 0 < y ≤ 1), a GaAs layer, Al x Ga 1-x As layer (0 ≤ x < 1), an Al x Ga y In 1-x-y P-layer (0 < x, 0 < y, x + y < 1), and an Al x Ga y In 1-x-y As layer (0 < x, 0 < y < 1, x + y ≤ 1).

[0079] The infrared emission layer is in particular preferably an in x Ga 1-x As layer (0 ≤ x < 1) or an Al x Ga 1-x As layer (0 ≤ x < 1). Thus, it is possible to provide a substrate with an epitaxial layer that has an emission wavelength around 900 nm and is suitable for an optical device such as a VCSEL.

[0080] The following is an overview of the structure of the substrate with an epitaxial layer, with reference to Fig. 5 described. Fig. Figure 5 is an illustrative diagram describing a substrate with an epitaxial layer according to the present embodiment. A substrate 300 with an epitaxial layer according to the present embodiment comprises a semi-insulating GaAs single-crystal substrate 100 and an epitaxial layer 200 formed by epitaxial growth on a first major surface of the semi-insulating GaAs single-crystal substrate 100. The epitaxial layer 200 comprises a first DBR layer 210, an infrared emission layer 220, and a second DBR layer 230 in the order listed, closer to the semi-insulating GaAs single-crystal substrate 100. The first DBR layer 210 can be a P-type DBR layer, and the second DBR layer 230 can be an N-type DBR layer.Although not shown in the figure, the epitaxial layer 200 may also include a current-limiting layer located at least between the first DBR layer 210 and the infrared emission layer 220, between the second DBR layer 230 and the infrared emission layer 220, and between the interior of the first DBR layer 210 and the interior of the second DBR layer 230. The current-limiting layer can exert a lensing effect by efficiently injecting current into an active region. Any other layer, such as a spacer layer and / or a contact layer, may also be included between the first DBR layer 210 and the infrared emission layer 220, as well as between the second DBR layer 230 and the infrared emission layer 220.

[0081] The substrate 300 with an epitaxial layer having the structure described above is suitable for an optical device such as a VCSEL because it exhibits both the properties of high near-infrared transmittance and low dislocation capability found in a semi-insulating GaAs single-crystal substrate 100. For example, a VCSEL can be formed on the substrate 300 with an epitaxial layer by forming not only a P-type semiconductor contact layer and an anode electrode on the semi-insulating GaAs single-crystal substrate 100, but also an N-type semiconductor contact layer and a cathode electrode on the second DBR layer 230. [Method for the production of semi-insulating gallium arsenide single crystals]

[0082] A process for producing a semi-insulating gallium arsenide single crystal (semi-insulating GaAs single crystal) need not be particularly restricted, as long as it is a process capable of producing a semi-insulating GaAs single crystal substrate with each of the properties of light absorption coefficient with respect to near-infrared light at a wavelength of 940 nm, EPD, resistivity, and the like, as described above. However, a semi-conducting GaAs single crystal is preferably obtained by, for example, the following fabrication process, since the semi-conducting GaAs single crystal substrate with each of these properties is obtained with a favorable processing yield.

[0083] In other words, a method for producing a semi-insulating GaAs single crystal according to the present embodiment is a method for producing a semi-insulating GaAs single crystal using a vertical boat process. The method for producing a semi-insulating GaAs single crystal comprises a step to prepare a single-crystal growth apparatus comprising at least one cylindrical crucible and a heating element that heats the crucible (first step); a step to pick up a seed crystal at a lower section of the crucible and to pick up a volume of gallium arsenide (GaAs) at an upper section compared to the seed crystal in the crucible (second step, hereinafter also referred to as the "raw material feeding step"); and a step of heating the crucible by the heating element to partially melt the GaAs and the seed crystal, thereby obtaining not only a GaAs melt,but also the GaAs melt and a residue of the seed crystal are brought into contact (third step, hereinafter also referred to as the "raw material melting step"), and a step of growing a crystal on the seed crystal in the GaAs melt to obtain a semi-insulating GaAs single crystal (fourth step). The step of obtaining a semi-insulating GaAs single crystal is carried out by satisfying a relationship between the following formula 4, formula 5 and formula 6. 0.20°C / mm≤X≤0.30°C / mm X+0.0012°C / mm2×Y≤Z1≤X+0.0024°C / mm2×Y 0.26°C / mm≤Z2≤0.42°C / mm In Formula 4, Formula 5 and Formula 6 X represents a temperature gradient along the axial direction of the crucible, measured with as the center of an interface between the crystal and the gallium arsenide melt, and the unit of the temperature gradient is °C / mm. Y represents a distance from the interface to a first reference point in the crystal, and the unit of distance is mm. Z1 represents a temperature gradient along the axial direction of the crucible, measured with the first reference point as the center point, and the unit of the temperature gradient is °C / mm. Z2 represents a temperature gradient along the axial direction of the crucible, measured with the first reference point at a distance of 50 mm from the interface to the first reference point as its center point, and the unit of the temperature gradient is °C / mm.

[0084] According to the fabrication process with these characteristics, it is possible to obtain a semi-insulating GaAs single crystal that exhibits both high near-infrared transmittance and low dislocation capability. Furthermore, the semi-insulating GaAs single crystal can be used to obtain a semi-insulating gallium arsenide single-crystal substrate that also possesses high near-infrared transmittance and low dislocation capability, and is therefore suitable for optical devices such as VCSELs.

[0085] The inventors have developed a method for growing a semi-insulating GaAs single crystal while suppressing dislocations as much as possible. This is achieved by critically controlling the growth temperature of the semi-insulating GaAs single crystal under specific conditions during its fabrication using a vertical boat process. Specifically, not only is the temperature of an interface between a growth-strengthened semi-insulating GaAs single crystal and a gallium arsenide melt in contact with the semi-insulating GaAs single crystal critically controlled, but also the temperature within the strengthened semi-insulating GaAs single crystal itself. This ensures that a step is performed to obtain the semi-insulating GaAs single crystal with a temperature gradient determined by Formulas 4, 5, and 6 described above.The inventors have thus established that a semi-insulating GaAs single crystal with low dislocation is obtained regardless of a low support concentration. The inventors have also designed a semi-insulating GaAs single-crystal substrate that exhibits both high near-infrared transmittance and low dislocation capability by utilizing the semi-insulating GaAs single crystal.

[0086] The "processing yield" here refers to the proportion in which a favorable semiconducting GaAs single-crystal substrate is obtained in a serial process for the production of a semiconducting GaAs single crystal and a substrate thereof. The term "favorable" refers to the absence of cracks, defects, or the like in a semi-insulating GaAs single-crystal substrate precursor, a semi-insulating GaAs single-crystal substrate, and the like in a serial process that includes growing a semi-insulating GaAs single crystal and cutting the crystal to a desired thickness to obtain a semi-insulating GaAs single-crystal substrate precursor, and further grinding and machining an outer circumference of the GaAs single-crystal substrate precursor to obtain a semi-insulating GaAs single-crystal substrate.In the following, a method for producing a semi-insulating GaAs single crystal according to the present embodiment and a method for producing a semi-insulating GaAs single crystal substrate comprising the single crystal are described with reference to . Fig. 6 to Fig. 8 described in more detail.

[0087] Fig. Figure 6 is a flowchart illustrating an overview of a process for the preparation of a semi-insulating gallium arsenide single-crystal substrate according to the present embodiment. Fig. Figure 7 is an illustrative diagram relating to a process for producing a semi-insulating gallium arsenide single crystal according to the present embodiment and describing a step for obtaining a semi-insulating gallium arsenide single crystal using a single-crystal fabrication apparatus. Fig. Figure 8 is another illustrative diagram relating to a method for producing a semi-insulating gallium arsenide single crystal according to the present embodiment and describing a step for obtaining a semi-insulating gallium arsenide single crystal using a single-crystal fabrication apparatus.

[0088] The present embodiment is a method for producing a semi-insulating GaAs single crystal using a vertical boat process. Examples of vertical boat processes include a vertical Bridgman process (VB process), a vertical temperature gradient freezing (VGF process), and a hybrid process combining a VB process and a VGF process. Hereinafter, a method for producing a semi-insulating GaAs single crystal, for example, using a VB process, is described. In other words, the fabrication method is a method for producing a semi-insulating GaAs single crystal using a VB process and can be implemented as shown in a flowchart in Fig. Figure 5 illustrates the process, which includes step S10 (first step) of preparing a single-crystal growth apparatus comprising at least one cylindrical crucible and a heating element that heats the crucible; step S20 (second step: raw material loading step) of picking up a seed crystal at a lower section of the crucible and picking up GaAs mass at an upper section compared to the seed crystal in the crucible; step S30 (third step: raw material melting step) of heating the crucible by the heating element to partially melt the GaAs and the seed crystal, thereby not only obtaining a GaAs melt but also bringing the GaAs melt and a residue of the seed crystal into contact; and step S40 (fourth step) of growing a crystal on the seed crystal in the GaAs melt to obtain a semi-insulating GaAs single crystal.In particular, step S40 for obtaining a semi-insulating GaAs single crystal comprises a first growth step S41, a second growth step S42, and a third growth step S43 for growing a semi-insulating GaAs single crystal in the single-crystal growth apparatus. This first growth step S41, this second growth step S42, and this third growth step S43 are described below.

[0089] Furthermore, in the manufacturing process, step S50 (fifth step, hereinafter also referred to as the "cutting step") for cutting the semi-insulating GaAs single crystal obtained by the single-crystal growth step into a wafer shape to extract the semi-insulating GaAs single crystal, and step S60 (sixth step) for grinding an outer circumference of the semi-insulating GaAs single crystal extracted in the cutting step and for processing, such as polishing, a surface of the crystal to obtain a semi-insulating GaAs single-crystal substrate, are preferably carried out in the order listed. Thus, a semi-insulating GaAs single-crystal substrate can be obtained from the semi-insulating GaAs single crystal with a favorable processing yield. Each step of the present manufacturing process is described in detail below. < First step: Preparing the apparatus for single crystal growth >

[0090] The first step is step S10, in which a device for growing a single crystal is prepared, comprising at least one cylindrical crucible and a heating element that heats the crucible. In this step, for example, a device for growing a single crystal 5 is prepared, comprising a crucible 51 and a heating element 73, as shown in Fig. 7 to Fig. Figure 8 illustrates this. Thus, the above-described method for producing a semi-insulating GaAs single crystal using a vertical boat process can be supported.

[0091] The in Fig. The apparatus 5 for growing a single crystal, as illustrated in Figure 7, comprises a cylindrical crucible 51 and a heating element 73 for heating the crucible 51. The crucible 51 includes a holding section for the seed crystal and a single-crystal growth section connected to the holding section. The holding section for the seed crystal is a cylindrical area with a cylindrical cavity section in which an opening for connection to the single-crystal growth section is formed on one side and a bottom wall is formed on the opposite side. The holding section can hold a gallium arsenide seed crystal (GaAs seed crystal) 61 in the cavity section. The single-crystal growth section comprises a conical section and a straight body section 9.The conical section has a conical shape and is connected to the seed crystal holding section at the side with the smaller axial diameter. The straight body section 9 has a hollow cylindrical shape and is connected to the side with the larger axial diameter of the conical section. The single-crystal growth section serves to hold a gallium arsenide raw material (GaAs raw material) in solid form. Furthermore, the single-crystal growth section serves to freeze a GaAs raw material (hereinafter also referred to as "gallium arsenide melt 82 (GaAs melt 82)") that is heated and thus brought into a molten state, in order to grow a semi-insulating GaAs single crystal 81. Here, the crucible 51 can be made of various materials that are resistant to the temperature at which GaAs melts.For example, pyrolytic boron nitride (PBN) is well suited as a material for crucible 51.

[0092] Furthermore, the device for growing single crystals 5 comprises a crucible holder 71, which holds the crucible 51, and a heating element 73, which is arranged to surround an outer surface radially to the crucible 51. The material of the crucible holder 71 can be, for example, quartz, aluminum oxide, or silicon carbide. The heating element 73 is arranged such that two such elements surround an outer surface radially to the crucible 51 to heat the crucible 51. The heating element 73 used here can, for example, be a known electric heater. The power of the heating element 73 can be controlled independently for each element. In particular, the heating element 73 is divided into a plurality of parts with respect to each element in a direction perpendicular to the axis of the crucible 51, in order to form several stages in some cases.In this case, the power of the heating element 73 can be controlled independently with respect to one of the parts designed as multiple stages, and therefore the temperature of the contents in the crucible 51 can be set along the axial direction of the crucible 51.

[0093] The device 5 for growing a single crystal preferably comprises one or more thermocouples 75 on an outer side in the radial direction of the crucible 51, as shown in Fig. Figure 7 illustrates this. In this case, the position of the thermocouples 75 can be shifted in a direction parallel to the axial direction of the crucible 51. The thermocouples 75 used here can, for example, be known temperature monitors. The apparatus 5 for growing a single crystal comprises such a crucible 51, a crucible holder 71, a heating element 73, and one or more thermocouples 75 for controlling the temperature around an interface between a GaAs seed crystal 61 and a GaAs melt 82, which is in contact with the GaAs seed crystal 61 or a solidified semi-insulating GaAs single crystal 81, and the temperature in the solidified semi-insulating GaAs single crystal 81, such that the temperatures correspond to a temperature gradient derived from formulas 4, 5, and 6 in a single-crystal growth step described below. < Second step: Raw material supply step >

[0094] The second step is step S20, in which a seed crystal is placed in a lower section of the crucible and GaAs raw material is placed in an upper section, opposite the seed crystal in the crucible. In this second step, materials (GaAs seed crystal 61 and GaAs raw material in bulk form) required for the growth of semi-insulating GaAs single crystals 81 in the single-crystal growth device 5 are prepared and placed at predetermined positions within the device. This second step may include the subsequent seed crystal loading step and the GaAs polycrystal loading step.

[0095] In the first step of seeding the GaAs seed crystal, a GaAs seed crystal 61 is placed into the cavity section of the seed crystal holding section of the crucible 51. A conventionally known method can be used for seeding the GaAs seed crystal 61 into the seed crystal holding section. Next, in the step of feeding GaAs polycrystals, for example, a plurality of bulk GaAs raw materials consisting of GaAs polycrystals are loaded and stacked on the conical section and the straight body section 9 in the single-crystal growth section of the crucible 51. Such GaAs raw materials used here can also include portions that are inferior to the GaAs single crystal with respect to their physical properties, and so on. Preferably, a conventionally known sealant (e.g., a sealant made of B₂O₃ (boron oxide)) is applied to the GaAs raw materials. < Third step: Raw material smelting step >

[0096] The third step, S30, involves heating the crucible with the heating element to partially melt the GaAs and the seed crystal. This process not only yields a GaAs melt but also brings the GaAs melt and a residue of the seed crystal into contact. In this third step, a section of the GaAs seed crystal 61 and the GaAs raw material in bulk are melted to bring the GaAs seed crystal 61 and the GaAs melt 82 into contact at an interface between them, thus producing a semi-insulating GaAs single crystal 81. Specifically, the crucible 51, containing the GaAs seed crystal 61 and the GaAs raw material in bulk, is first placed in the crucible holder 71 in the single-crystal growth apparatus 5. Then, current is applied to the heating element 73 to heat the crucible 51.When the crucible 51 is heated, this heating is achieved by controlling the heating element 73, such that the temperature of an interface between the GaAs seed crystal 61 and the bulk GaAs raw materials in the cavity section of the seed crystal holding section of the crucible 51 exceeds the melting point of GaAs. Thus, the bulk GaAs raw material is melted to provide GaAs melt 82. Furthermore, any GaAs raw material located at the interface with the GaAs seed crystal 61 is also defined as GaAs melt 82, and a portion of the GaAs seed crystal 61 (corresponding to approximately 50 vol% of the interface between the GaAs seed crystal 61 and the GaAs melt 82) can also be melted. < Fourth step: Step of the semi-insulating GaAs single crystal >

[0097] The fourth step is step S40, in which a crystal is grown on the seed crystal in the GaAs melt to obtain a semi-insulating GaAs single crystal. In the fourth step, the first growth step S41, the second growth step S42, and the third growth step S43, as described below, are carried out in the specified order to obtain a semi-insulating GaAs single crystal, thereby growing a semi-insulating GaAs single crystal 81. In particular, the fourth step is carried out satisfying the following relationship between Formula 4, Formula 5, and Formula 6. 0.20°C / mm≤X≤0.30°C / mm X+0.0012°C / mm2×Y≤Z1≤X+0.0024°C / mm2×Y 0.26°C / mm≤Z2≤0.42°C / mm In Formula 4, Formula 5 and Formula 6, X represents a temperature gradient along the axial direction of the crucible, measured with as the center of an interface between the crystal and the gallium arsenide melt, and the unit of the temperature gradient is °C / mm. Y represents a distance from the interface to a first reference point in the crystal, and the unit of distance is mm. Z1 defines a temperature gradient along the axial direction of the crucible, measured with the first reference point as the center point, and the unit of the temperature gradient is °C / mm. Z2 represents a temperature gradient along the axial direction of the crucible, measured with the first reference point at a distance of 50 mm from the interface to the first reference point as its center point, and the unit of the temperature gradient is °C / mm.

[0098] The following section describes in more detail the first growth step S41, the second growth step S42 and the third growth step S43. (First growth stage)

[0099] The first growth step S41 is a step for solidification and thus for the growth of a semi-insulating GaAs single crystal 81 from the molten section of the GaAs seed crystal 61 and the GaAs melt 82 in the raw material melting step S30. In the first growth step S41, a predetermined temperature gradient is created along the axial direction of the crucible 51 at an interface between the GaAs seed crystal 61 and the GaAs melt 82 and at an interface between the solidified semi-insulating GaAs single crystal 81 and the GaAs melt 82, with the respective interfaces as their centers, so that the relationship of formula 4 is satisfied. In particular, the power of the heating element 73 is controlled such that the temperature at a position closer to the GaAs seed crystal 61 and the temperature at a position closer to the GaAs melt 82 in the axial direction of the crucible 51 are each lower or higher.The temperature is higher and a temperature gradient X along the axial direction of the crucible 51 with the interface between the GaAs seed crystal 61 and the GaAs melt 82 as its center is 0.2 to 0.3°C / mm (0.20°C / mm ≤ X ≤ 0.30°C / mm). In conjunction with this, the heating element 73 is moved along the axial direction of the crucible 51 while maintaining the temperature gradient X described above, and the semi-insulating GaAs single crystal 81 is further consolidated to allow an end section (hereinafter also referred to as the "growth end section") of the semi-insulating GaAs single crystal 81 to grow upwards in the axial direction of the crucible 51 (vertical direction).

[0100] An interface between the growth end section of the semi-insulating GaAs single crystal 81 and the GaAs melt 82 is also shifted upwards in the axial direction of the crucible 51 (vertical direction), and the power of the heating element 73 is controlled such that the temperature of the interface also satisfies the relationship of formula 4 and the temperature gradient X, which is formed along the axial direction of the crucible 51 with the interface as its center, is maintained. Furthermore, in the first growth stage S41, the power of the heating element 73 is controlled such that the relationship of formula 5 is satisfied, thereby maintaining a predetermined temperature gradient Z1 (X + 0.0012°C / mm²). 2 × Y ≤ Z1 ≤ X + 0.0024°C / mm 2 × Y) along the axial direction of the crucible 51 with a first reference point, described below, formed in semi-insulating GaAs single crystal 81. The “first reference point” denotes a position located a distance (unit: mm) from the interface, specified by Y in Formula 5, from the interface in the direction of the semi-insulating GaAs single crystal 81 along the axial direction of the crucible 51 (vertical direction). The range of Y in Formula 5 can be from 0 to 100 mm. The speed of movement of the heating element 73 along the axial direction of the crucible 51 can be 0.3 mm / h or more and 5.0 mm / h or less. Alternatively, the crucible 51 itself can be moved along the axial direction at the aforementioned speed instead of the heating element 73.

[0101] In a first growth step S41, such a process can be carried out to raise the growth end section (interface between the growth end section and the GaAs melt 82) of the semi-insulating GaAs single crystal 81 to a connecting section between the conical section and the straight body section 9 of the single crystal growth section of the crucible 51 (see Fig. 7). (Second growth phase)

[0102] The second growth step S42 is performed after the first growth step S41 and involves freezing the GaAs melt 82 in the straight body section 9 of the single-crystal growth section of the crucible 51, thereby raising the end growth section of the semi-insulating GaAs single crystal 81 axially (vertically). In the second growth step S42, the power of the heating element 73 is also controlled such that the temperature of the interface between the end growth section of the semi-insulating GaAs single crystal 81 and the GaAs melt 82 satisfies the relationship of formula 4. Thus, the temperature gradient X formed along the axial direction of the crucible 51 with the interface as its center can be maintained.The power of the heating element 73 is controlled such that the relationship of formula 5 is satisfied, thereby maintaining the predetermined temperature gradient Z1 along the axial direction of the crucible 51 with the first reference point in the semi-insulating GaAs single crystal 81 as its center. Specifically, in the second growth stage S42, the power of the heating element 73 is controlled such that a temperature gradient Z2 along the axial direction of the crucible 51 with the first reference point as its center is 0.26 to 0.42°C / mm (0.26°C / mm ≤ Z2 ≤ 0.42°C / mm), so that the relationship of formula 6 is satisfied in the case of a distance of 50 mm (Y = 50) from the interface to the first reference point.

[0103] In the second growth step S42, the heating element 73 can be pulled upwards in the axial (vertical) direction to further freeze the GaAs melt 82 in the straight body section 9, causing the GaAs single crystal 81 to grow upwards in the axial (vertical) direction. The second growth step S42 can raise the end-growth section (interface between the end-growth section and the GaAs melt 82) of the semi-insulating GaAs single crystal 81 to an upper section of the straight body section 9 in the single-crystal growth section of the crucible 51 (see Fig. 8) In the second growth step S42, the crucible 51 itself can be moved along the axial direction at the speed mentioned above, instead of the heating elements 73, as in the first growth step S41.

[0104] In the second growth step S42, the heating element 73 can be pulled upwards in the axial (vertical) direction to further freeze the GaAs melt 82 in the straight body section 9, causing the GaAs single crystal 81 to grow upwards in the axial (vertical) direction. The second growth step S42 can raise the end-growth section (interface between the end-growth section and the GaAs melt 82) of the semi-insulating GaAs single crystal 81 to an upper section of the straight body section 9 in the single-crystal growth section of the crucible 51 (see Fig. 8) In the second growth step S42, the crucible 51 itself can also be moved along the axial direction at the speed mentioned above, instead of the heating elements 73, as in the first growth step S41. Even in a case where formulas 5 and 6 are not satisfied in the first growth step S41 and in the second growth step S42, the EPD formed on the first main surface tends to easily 300 cm² in the etch test performed on the semi-insulating gallium arsenide single-crystal substrate obtained from the semi-insulating GaAs single crystal. -2 to exceed.

[0105] The temperature gradients X, Z1 and Z2 described above can be determined using measurements with thermocouple(s) 75. (Third growth stage)

[0106] The third growth step S43 is performed after the second growth step S42 and completes the freezing of the GaAs melt 82 remaining in the straight body section 9. The third growth step S43 is complete, and thus the single-crystal growth step is finished. As described above, the semi-insulating GaAs single crystal 81 is produced in crucible 51 and subsequently removed from crucible 51. <Verfahren zur Herstellung von halbisolierenden Galliumarsenid-Einkristall-Substraten>

[0107] The above-described method for producing a semi-insulating GaAs single crystal is carried out to obtain a semi-insulating GaAs single crystal with low dislocation density, independent of a low support concentration. Furthermore, a method for producing a semi-insulating GaAs single crystal according to the present embodiment is preferably carried out by performing, in the sequence listed, step S50 (cutting step: fifth step) of cutting the semi-insulating GaAs single crystal into a disk shape to remove the semi-insulating GaAs single crystal, and step S60 (sixth step) of grinding an outer circumference of the semi-insulating GaAs single crystal removed in cutting step S50 and processing, for example, polishing, a surface of the crystal to obtain a semi-insulating GaAs single-crystal substrate.Thus, a semi-insulating GaAs single-crystal substrate with a circular first main surface can be produced. (Fifth and sixth steps: cutting step and step to obtain a semi-insulating GaAs single-crystal substrate)

[0108] The fifth step is step S50, in which the semi-insulating GaAs single crystal is sliced ​​into a disk shape and removed. Furthermore, the sixth step is step S60, in which an outer circumference of the semi-insulating GaAs single crystal removed in step S50 is ground and a surface of the crystal is processed, for example by polishing, to obtain a semi-insulating GaAs single-crystal substrate with a circular primary surface. The slicing step and the step to obtain a semi-insulating GaAs single-crystal substrate can each be carried out using a conventionally known slicing, outer circumference grinding, surface polishing, or similar process in such a process for producing a GaAs single-crystal substrate using a VB process. <vorgehen>

[0109] As described above, a semi-insulating GaAs single-crystal substrate with a circular primary surface can be fabricated. The fabrication method enables the production of a semi-insulating GaAs single crystal in which dislocations are suppressed as much as possible by critically controlling the growth temperature under specific conditions. Thus, the method allows the fabrication of a semi-insulating GaAs single crystal with low dislocation, regardless of the support concentration, and can therefore provide a semi-insulating GaAs single-crystal substrate suitable for optical devices requiring high near-infrared transmittance and low dislocation capability, such as a VCSEL.Furthermore, a semi-insulating GaAs single-crystal substrate obtained by the above-mentioned steps is advantageous in terms of processing yield. Examples

[0110] The present disclosure is described in more detail below by means of examples, but the present disclosure is not limited thereto. In each of the samples described below, a device for growing single crystals 5, as in Fig. 7 and Fig. 8 shown, used to create a semi-insulating GaAs single crystal with the <100> -direction as the growth direction using a vertical boat method (e.g., VB method). Furthermore, a semi-insulating GaAs single-crystal substrate was obtained from the semi-insulating GaAs single crystal, in which the plane orientation of a first major surface was the {100} plane. In the following description, samples 1 to 4 correspond to the examples and samples 101 to 106 to the comparison examples. [Example 1]

[0111] First, each semi-insulating GaAs single-crystal substrate of samples 1 to 4 and samples 101 to 106 was prepared as follows. < Sample 1> (First Step)

[0112] As described above, a device 5 for growing single crystals, comprising a crucible 51 and a heating element 73, as shown in Fig. 7 and Fig. Figure 8 illustrates how the crucible 51 was manufactured. Here, the inner diameter of the straight body section 9 of the crucible 51, which was used in the manufacture of sample 1, was 155 mm. (Second step)

[0113] A GaAs seed crystal 61 and bulk GaAs raw material, required for the growth of semi-insulating GaAs single crystals 81 in a single-crystal growth apparatus 5, were prepared. The GaAs seed crystal 61 was prepared by a conventionally known method. Furthermore, a variety of bulk GaAs raw materials of commercially available polycrystalline GaAs were loaded and stacked into the conical and straight sections of the crucible 51. A sealant of B₂O₃ was also applied to the bulk GaAs raw materials. (Third step)

[0114] The crucible 51, into which the GaAs seed crystal 61 and a bulk GaAs raw material had been placed, was inserted into the crucible holder 71 of the apparatus 5 for growing a single crystal. Current was then applied to the heating element 73 to induce heating such that the temperature of an interface between the GaAs seed crystal 61 and the bulk GaAs raw material in the crucible 51 exceeded the melting point of GaAs. Thus, the GaAs raw material located at the interface with the GaAs seed crystal 61 was defined as the GaAs melt 82, and a section of the GaAs seed crystal 61 (corresponding to approximately 50 vol% compared to a region within the GaAs seed crystal 61, the region being close to the GaAs melt 82) was also melted. (Fourth step) - First growth step -

[0115] The heating element 73 for heating the crucible 51 was controlled such that a temperature gradient X of 0.26 °C / mm was formed along the axial direction of the crucible 51 at an interface between the semi-insulating GaAs seed crystal 61 and the GaAs melt 82, and at an interface between the solidified semi-insulating GaAs single crystal 81 and the GaAs melt 82, with the respective interfaces as their centers, so that the relationship of formula 4 was satisfied. Here, the control was implemented such that the temperature at a position closer to the GaAs seed crystal 61 and the temperature at a position closer to the GaAs melt 82 were lower or higher, respectively, in the axial direction of the crucible 51.Furthermore, this control was implemented such that the temperature gradient Z1 along the axial direction of the crucible 51, with a first reference point, described below, of the semi-insulating GaAs single crystal 81 as its center, follows the relationship of formula 5 (X + 0.0012°C / mm. 2 × Y ≤ Z1 ≤ X + 0.0024°C / mm 2 x Y). In conjunction with this, the heating element 73 was moved along the axial direction of the crucible 51, maintaining a temperature gradient X of 0.26 °C / mm at the interface, and the semi-insulating GaAs single crystal 81 was further solidified to allow a growth end section of the semi-insulating GaAs single crystal 81 to grow upwards in the axial direction of the crucible 51 (vertical direction) to a connection section between a conical section and a straight body section of the crucible 51. The winding rate of the heating element 73 during winding was 2 mm / h.

[0116] For example, the temperatures at the interface between the semi-insulating GaAs seed crystal 61 and the GaAs melt 82, as well as at the interface between the solidified semi-insulating GaAs single crystal 81 and the GaAs melt 82, were 1238 °C. -Second growth phase-

[0117] The heating element 73 for heating the crucible 51 was subsequently controlled such that the GaAs melt 82 solidified in the straight section of the crucible 51, thereby raising the growth end section of the semi-insulating GaAs single crystal 81 in the axial direction of the crucible 51 (vertical direction). The power of the heating element 73 was controlled such that the temperature of an interface between the growth end section of the semi-insulating GaAs single crystal 81 and the GaAs melt 82 satisfied the relationship of formula 4 and the temperature gradient X (0.26 °C / mm), which was formed along the axial direction of the crucible 51 with the interface as its center, was maintained.Furthermore, the power of the heating element 73 was controlled such that the relationship of formula 6 was satisfied, so that when the first reference point of the semi-insulating GaAs single crystal 81 was located at a position 50 mm away from the interface in the direction of the semi-insulating GaAs single crystal 81, a temperature gradient Z2 of 36 °C / mm was formed with the midpoint at a position 50 mm away from the interface in the direction of the semi-insulating GaAs single crystal 81.

[0118] The power of the heating element 73 was controlled such that the relationship of formula 5 was satisfied, and thus, for example, if the first reference point of the semi-insulating GaAs single crystal 81 was located 100 mm from the interface to the semi-insulating GaAs single crystal 81, a temperature gradient Z1 of 0.48 °C / mm was formed along the axial direction of the crucible 51, with the midpoint located 100 mm from the interface in the direction of the semi-insulating GaAs single crystal 81. Here, the temperature at a point 100 mm from the interface in the direction of the semi-insulating GaAs single crystal 81 was 1201 °C. -Third growth phase-

[0119] The GaAs melt 82 in the straight section of the crucible 51 was subsequently frozen to complete the freezing of the remaining GaAs melt 82. Accordingly, a semi-insulating GaAs single crystal 81 was produced in the crucible 51. The semi-insulating GaAs single crystal 81 was then removed from the crucible 51 using a conventionally known method. (Fifth step and sixth step)

[0120] The conventional cutting process, the external circumferential grinding process, and the surface polishing process were applied to the semi-insulating GaAs single crystal 81 removed from the crucible 51. Thus, a first end face (hereinafter referred to as "F") and a second end face (hereinafter referred to as "B") of the semi-insulating GaAs single crystal 81, each facing the GaAs seed crystal 61 and an upper section of the crucible 51 respectively, were cut to a thickness of 755 mm. Furthermore, their outer circumferences were ground and their surfaces polished to produce two semi-insulating GaAs single-crystal substrates, each with two circular main surfaces (first main surface and second main surface). Accordingly, two semi-insulating GaAs single-crystal substrates, each with a diameter (D) of 152.4 mm, were obtained as sample 1. <Probe 2>

[0121] Two semi-insulating GaAs single-crystal substrates of sample 2 were obtained in the same way as in sample 1, except that each of the temperature gradients X, Z1 and Z2 in the first and second growth steps was changed as shown in Table 1 below. <Probe 3>

[0122] Two semi-insulating GaAs single-crystal substrates of sample 3 were obtained in the same way as in sample 1, except that the inner diameter of the crucible 51 was modified accordingly, so that semi-insulating GaAs single-crystal substrates with a diameter as shown in Table 1 below were obtained, and each of the temperature gradients X, Z1 and Z2 in the first and second growth steps was changed as shown in Table 1 below. <Probe 4>

[0123] Two semi-insulating GaAs single-crystal substrates of sample 4 were obtained in the same way as in sample 1, except that the inner diameter of the crucible 51 was modified accordingly, so that semi-insulating GaAs single-crystal substrates with a diameter as shown in Table 1 below were obtained, and each of the temperature gradients X, Z1 and Z2 in the first and second growth steps was changed as shown in Table 1 below. <Probe 101>

[0124] Two semi-insulating GaAs single-crystal substrates of sample 101 were obtained by a replication study of a method for the preparation of a semi-insulating GaAs single-crystal substrate according to Example II-1, disclosed in PTL 4. In this case, the temperature gradients X, Z1 and Z2 in the first growth step and in the second growth step were as shown in Table 1 below. <Probe 102>

[0125] Two semi-insulating GaAs single-crystal substrates of sample 102 were obtained by a replication study of a process for the preparation of a semi-insulating GaAs single-crystal substrate according to Example II-4 disclosed in PTL 4. In this case, the temperature gradients X, Z1 and Z2 in the first growth step and in the second growth step were as shown in Table 1 below. <Probe 103>

[0126] Two semi-insulating GaAs single-crystal substrates of sample 103 were obtained by replication of a method for producing a semi-insulating GaAs single-crystal substrate according to Example 1, disclosed in Japanese patent application No. H11-335194. In this case, the temperature gradients X, Z1 and Z2 in the first and second growth steps were as shown in Table 1 below. <Probe 104>

[0127] An ingot of sample 104 was obtained by a replication study of a method for preparing an ingot disclosed in PTL 1, and two semi-insulating GaAs single-crystal substrates of sample 104 were obtained from the ingot. In this case, the temperature gradients X, Z1 and Z2 in the first growth step and in the second growth step were as shown in Table 1 below. <Probe 105>

[0128] Two semi-insulating GaAs single-crystal substrates of sample 105 were obtained in the same way as in sample 1, except that each of the temperature gradients X, Z1 and Z2 in the first growth and second growth steps was changed as shown in Table 1 below. <Probe 106>

[0129] Two semi-insulating GaAs single-crystal substrates of sample 106 were obtained in the same manner as in sample 1, except that the inner diameter of the crucible 51 was modified accordingly, so that semi-insulating GaAs single-crystal substrates with a diameter as shown in Table 1 below were obtained, and each of the temperature gradients X, Z1 and Z2 in the first and second growth steps was changed as shown in Table 1 below. < Evaluation of characteristics >

[0130] Each of the properties of the light absorption coefficient was determined with respect to near-infrared light at a wavelength of 940 nm, the EPD, the resistivity, the carrier concentration, the electron mobility, the residual voltage, the EL2 concentration, and the average atomic concentration of carbon for each sample by performing the aforementioned measurement procedures with respect to each of the semi-insulating GaAs single-crystal substrates of samples 1 to 4 and samples 101 to 106. The results are presented in Table 1 and Table 2.In Table 1 and Table 2, “(F)” in the entry for each of these features means that the first principal surface of the semi-insulating GaAs single-crystal substrate is derived from a first end face of the semi-insulating GaAs single crystal 81 (or ingots), and “(B)” in the dot with respect to each of these features means that the first principal surface of the semi-insulating GaAs single-crystal substrate is derived from a second end face of the semi-insulating GaAs single crystal 81 (or ingots). [Table 1] Table 1 Probe1 Probe2 Probe3 Probe4 Probe101 Probe102 Probe103 Probe104 Probe105 Probe106 Durchmesserr 152,4 152,4 101,6 202,5 101,6 152,4 152,4 152,4 152,4 202,5 X(°C / mm) 0,26 0,25 0,25 0,22 0,63 0,60 0,62 0,24 0,25 0,35 Z2 (Y=50)(°C / mm) 0,36 0,35 0,36 0,32 1,28 1,39 1,35 0,50 0,40 0,62 Z1 (Y=100)(°C / mm) 0,48 0,46 0,48 0,45 1,22 1,30 1,25 0,50 0,52 0,64 EPD (F)(cm -2 ) 194 260 125 295 5900 6000 3000 427 416 850 EPD (B)(cm -2 ) 173 98 89 283 6500 6800 4600 558 640 930 Specific resistance ρ(F)(×10 8 Ω·cm) 2,8 2,1 1,9 1,6 1,2 2,3 1,8 2,3 1,8 1,9 Specific resistance ρ(B)(x10 8 Q.cm) 3,1 2,9 2,8 2,3 3,4 4,0 2,4 3,0 2,4 2,4 Light absorption coefficient (F) (cm²) -1 ) 1,17 1,24 1,11 1,20 1,25 1,13 1,3 1,33 1,28 1,3 Light absorption coefficient (B) (cm²) -1 ) 1,05 1,21 1,24 1,12 1,30 1,29 1,22 1,23 1,15 1,35 [Table 2] Table 2 Probe1 Probe2 Probe3 Probe4 Probe101 Probe102 Probe103 Probe104 Probe105 Probe106 Electron mobility (F) (cm²) 2 / V·s) 5500 6000 6300 6400 6300 5560 5910 5200 6300 5900 Electron mobility(B)(cm) 2 / V·s) 5300 5600 5600 5900 4800 4240 5800 4900 5900 5600 Carrier concentration (F)(x10 6 cm -3 ) 4,2 5,9 6,8 6,8 9,1 5,0 6,3 5,2 6,3 6,3 Carrier concentration n(B)(×10 6 cm -3 ) 3,8 4,0 4,2 4,8 4,0 3,3 5,4 4,1 4,9 5,2 Restspannung (F)(×10 -6 ) 2,5 2,7 1,8 4,2 3,1 7,0 6,2 3,1 2,9 5,0 Restspannung (B)(x10 -6 ) 2,9 2,8 2,0 4,8 3,5 10,0 8,3 3,5 4,1 6,2 EL2 concentration (F)(x10 15 cm -3 ) 8,9 9,2 8,8 8,2 10,0 10,0 12,0 10,0 8,7 8,7 EL2 concentration (B)(×10 15 cm -3 ) 8,7 8,9 8,7 7,9 9,1 10,0 12,0 9,2 8,5 8,5 Atomic carbon concentration (F) (x10 15 cm -3 ) 7,3 6,9 6,8 7,0 5,0 8,5 9,4 8,8 6,3 5,5 Atomic carbon concentration (B) (x10 15 cm -3 ) 7,5 7,2 7,0 7,2 9,9 11,0 9,8 9,8 7,0 7,1 Herstellungsausbeute(%) 93 91 94 90 10 5 15 82 79 55 <diskussion>

[0131] In each of samples 1 to 4, the light absorption coefficient of the GaAs single-crystal substrate with respect to near-infrared light at a wavelength of 940 nm was 1.5 cm. -1 or less, the EPD formed on the first main surface was 300 or less, and the resistivity of the semi-insulating GaAs single-crystal substrate, measured at 25°C by the Van der Pauw method, was 1.0 × 10 8 Ω×cm or more. From the above, it is evident that the semi-insulating GaAs single-crystal substrates of samples 1 to 4 can serve as semi-insulating GaAs single-crystal substrates suitable for an optical device requiring high near-infrared transmittance and low dislocation capability, such as a VCSEL. In particular, it can be expected that the semi-insulating GaAs single-crystal substrates of samples 1 to 4, according to the values ​​of the light absorption coefficient and the EPD, will exhibit a significantly improved yield in the fabrication of VCSELs or the like.It is understood that even if the first principal surface of the semi-insulating GaAs single-crystal substrate is derived from a first end face of the semi-insulating GaAs single-crystal 81 or from a second end face of the semi-insulating GaAs single-crystal 81, each of the properties in the first principal surface is excellent at a comparable level. In contrast, the semi-insulating GaAs single-crystal substrates of samples 101 to 106 were inferior to the semi-insulating GaAs single-crystal substrates of samples 1 to 4 in at least one of the aforementioned properties with respect to the light absorption coefficient for near-infrared light at a wavelength of 940 nm, the EPD, or the resistivity. [Example 2]< Production of VCSEL >

[0132] An infrared emission layer was deposited by epitaxial growth on the first main surface of each of the semi-insulating GaAs single-crystal substrates of samples 1 to 4 and samples 101 to 106 prepared in Example 1, using a conventionally known method to fabricate a vertical surface-emitting laser (VCSEL).

[0133] In particular, an epitaxy structure was formed on the first main surface of the semi-insulating GaAs single-crystal substrate of each specimen by an organometallic vapor phase epitaxy (OMVPE) process as a conventional method according to a method disclosed in Example 1 of Japanese patent application No. 2019-040953.In particular, an epitaxial structure comprising a DBR region of a p-type GaAs / p-type AlGaAs superlattice, a lower contact layer of C-doped GaAs, a lower spacer layer of AlGaAs, an infrared emission layer of an InGaAs / GaAs quantum well structure, a DBR semiconductor region of an n-type GaAs / AlGaAs superlattice, an upper section spacer layer of undoped GaAs, a current constriction layer of Si-doped AlAs, a second DBR region of an n-type GaAs / n-type AlGaAs superlattice structure, and an upper section contact layer of Si-doped GaAs were formed on the first main surface in the listed order. Specifically, a quantum well structure of an InGaAs / GaAs superlattice was formed. x Ga 1-x An As (x = 0.2) quantum well layer with a thickness of 5 nm and a GaAs barrier layer with a thickness of 7 nm as an infrared emission layer were grown in 6 cycles. Subsequently, a device fabrication process, such as electrode formation, was carried out to subdivide it into individual chips with a chip spacing of 0.5 mm × 0.5 mm to obtain each VCSEL (hereinafter also referred to as "VCSELs of Sample 1 to Sample 4 and Samples 101 to 106") corresponding to each of the semi-insulating GaAs single-crystal substrates of Sample 1 to Sample 4 and Samples 101 to 106. < Manufacturing yield of VCSEL >

[0134] The VCSELs of samples 1 to 4 and samples 101 to 106 were each subjected to an initial property evaluation and a high-temperature accelerated aging test by burn-in. In the initial property evaluation, a pass / fail distinction was made based on the light intensity applied at the same current. In the accelerated high-temperature aging test, the degree of aging after the accelerated aging process determined whether all chips that had passed the initial property evaluation were pass / fail. Specifically, the initial property evaluation was based on the light intensity at a current of 6 mA in the on-wafer state before chip fabrication.In the accelerated high-temperature degradation test, 40 devices were randomly selected after chip fabrication, subjected to a current of 12 mA and an ambient temperature of 80 °C for 100 hours, and after being returned to room temperature, their properties were compared with those before the high-temperature acceleration to determine whether they passed or failed. The final manufacturing yield was determined by expressing the product of the yields in both tests as a percentage. The results are shown in Table 2. <diskussion>

[0135] The VCSELs of samples 1 to 4 showed favorable fabrication yields compared to the VCSELs of samples 101 to 106. Therefore, the semi-insulating GaAs single-crystal substrates of samples 1 to 4 are likely suitable for optical devices such as VCSELs.

[0136] While embodiments and examples of the present disclosure are as described above, a suitable combination of configurations of each embodiment and example is also originally provided.

[0137] The embodiments and examples disclosed herein are to be considered illustrative and not in every respect as limiting. The scope of the present invention is not defined by the embodiments and examples above, but by the claims, and is intended to encompass all modifications within the meaning and scope of the claims. Reference symbol list

[0138] 1 Semiconducting gallium arsenide single crystal substrate (semiconducting GaAs single crystal substrate), 11 First main surface, 11a Rectangular cross-section, 11b Lattice, 100 Semiconducting gallium arsenide single crystal substrate (semiconducting GaAs single crystal substrate), 21 Electrode, 200 Epitaxial layer, 210 First DBR layer, 220 Infrared emission layer, 230 Second DBR layer, 300 Substrate with epitaxial layer, 5 Single crystal growth apparatus, 51 Crucible, 61 GaAs seed crystal, 71 Crucible holder, 73 Heating element, 75 Thermocouple, 81 Semiconducting GaAs single crystal, 82 GaAs melt, 9 Straight body section, O Center, OF Orientation surface, S10 Step for preparing the single crystal growth apparatus, S20 Step to feed the raw material, S30 Step to melt the raw material, S40 Step to obtain a semiconducting GaAs single crystal, S41 First growth step, S42 Second growth step, S43 Third growth step, S50 Cutting step,S60 Step to obtain a semi-insulating GaAs single-crystal substrate. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] US 2020 / 0190696

[0002] US 2020 / 0190697

[0002] US 2013 / 0320242

[0002] WO 2019 / 008663

[0002] WO 2019 / 008663

[0002] JP 11-335194

[0126] JP 2019-040953

[0133] Cited non-patent literature

[0000] Review of Scientific Instruments Vol. 64 No. 7, pp. 1815-1821 (1993

[0059] Applied Physics Letters, Volume 39, p. 747 (1981

[0066] JIS B 0601-2001

[0069] < / diskussion> < / diskussion> < / vorgehen> < / epitaxieschicht> < / anwendung> < / durchmesser>

Claims

[1] Semi-insulating gallium arsenide single crystal substrate with a circular first main surface, wherein a diameter of the semi-insulating gallium arsenide single crystal substrate is 95 mm or more and 205 mm or less, a light absorption coefficient of the semi-insulating gallium arsenide single-crystal substrate with respect to near-infrared light at a wavelength of 940 nm 1.5 cm -1 or less the number of etch pits per square centimeter formed on the first main surface in an etching test by immersion of the semi-insulating gallium arsenide single-crystal substrate in molten potassium hydroxide at 500 °C for 10 minutes is 300 or less, and a specific resistance of the semi-insulating gallium arsenide single crystal substrate, measured at 25 °C in a Hall measurement according to the Van der Pauw method, 1.0 × 10 8 Ω·cm or more. [2] Semi-insulating gallium arsenide single-crystal substrate according to claim 1, wherein the light absorption coefficient is determined by applying near-infrared light with a wavelength of 940 nm to the semi-insulating gallium arsenide single-crystal substrate at an angle of 85 degrees to measure the transmittance and reflectance of the near-infrared light of the semi-insulating gallium arsenide single-crystal substrate with an ultraviolet visible-infrared spectrophotometer, and assigning a numerical value of transmittance and a numerical value of reflectance and a numerical value of thickness of the semi-insulating gallium arsenide single-crystal substrate to the following equation 1, equation 2 and equation 3, and together with a reflectance in a reflection of the near-infrared light in the semi-insulating gallium arsenide single-crystal substrate: R+R(1−R)2exp(−2αd) / (1−r)=R* (1−R)2exp(−αd) / (1−r)=T* r=R2exp(2αd) where in equation 1, equation 2 and equation 3, R* represents the reflectance taking into account multiple reflections, measured with an ultraviolet-visible-infrared spectrophotometer, and the unit of reflectance is dimensionless. T* represents the transmittance taking into account multiple reflections, measured with an ultraviolet-visible-infrared spectrophotometer, and the unit of transmittance is dimensionless. α represents the light absorption coefficient, and the unit of the light absorption coefficient is cm. -1 is, R represents a reflectance value upon reflection of near-infrared light in the semi-insulating gallium arsenide single-crystal substrate, and a unit of reflectance upon reflection is dimensionless, and d represents the thickness of the semi-insulating gallium arsenide single crystal substrate and is a unit of thickness cm. [3] Semi-insulating gallium arsenide single crystal substrate according to claim 1 or claim 2, wherein a carrier concentration in the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C in a Hall measurement according to the Van der Pauw method, 8.0 × 10 6 cm -3 or less, and Electron mobility of the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C in a Hall measurement using the Van der Pauw method, 4500 cm⁻¹ 2 / V·s or more. [4] Semi-insulating gallium arsenide single-crystal substrate according to any one of claims 1 to 3, wherein an average value of a residual stress, as an absolute value of a difference between a stress along a radial direction of the first main surface and a stress along a tangential direction of the first main surface, 5.0 × 10 -6 or less. [5] Semi-insulating gallium arsenide single-crystal substrate according to any one of claims 1 to 4, wherein an EL2 concentration of the semi-insulating gallium arsenide single-crystal substrate is 7.5 × 10 15 cm -3 or more and 1.0 × 10 16 cm -3 or less. [6] Semi-insulating gallium arsenide single crystal substrate according to any one of claims 1 to 5, wherein the semi-insulating gallium arsenide single-crystal substrate contains carbon and an atomic concentration of carbon in the semi-insulating gallium arsenide single-crystal substrate 5.0 × 1015 cm -3 or more and 1.2 × 10 16 cm -3 or less. [7] Semi-insulating gallium arsenide single crystal substrate according to any one of claims 1 to 6 for use in a vertical surface-emitting laser. [8] Substrate comprising an epitaxial layer, wherein the substrate comprises the semi-insulating gallium arsenide single crystal substrate according to any one of claims 1 to 7, and an epitaxial layer arranged on the first main surface, wherein the epitaxial layer comprises an infrared emission layer. [9] Method for the preparation of a semi-insulating gallium arsenide single crystal using a vertical boat process, wherein the preparation method Preparing a device for growing a single crystal, comprising at least one cylindrical crucible and a heating element that heats the crucible, Providing a seed crystal at a lower section of the crucible and providing gallium arsenide mass at an upper section compared to the seed crystal in the crucible, Heating the crucible with the heating element to partially melt the gallium arsenide and the seed crystal, thereby not only obtaining a gallium arsenide melt, but also bringing the gallium arsenide melt and a residue of the seed crystal into contact, and Growing a crystal on the seed crystal in the gallium arsenide melt to obtain a semi-insulating gallium arsenide single crystal includes, wherein the obtaining of a semi-insulating gallium arsenide single crystal is carried out in accordance with the following formulas 4, 5 and 6: 0.20°C / mm≤X≤0.30°C / mm X+0.0012°C / mm2×Y≤Z1≤X+0.0024°C / mm2×Y 0.26°C / mm≤Z2≤0.42°C / mm where in Formula 4, Formula 5 and Formula 6, X represents a temperature gradient along an axial direction of the crucible, measured with an interface between the crystal and the gallium arsenide melt as the center point, and a unit of the temperature gradient is °C / mm. Y represents a distance from the interface to a first reference point in the crystal and is a unit of distance mm, Z1 represents a temperature gradient along an axial direction of the crucible, measured with the first reference point as the center, and is a unit of the temperature gradient °C / mm, and Z2 represents a temperature gradient along an axial direction of the crucible, measured with the first reference point at a distance of 50 mm from the interface to the first reference point as its center point, and a unit of the temperature gradient is °C / mm. [10] Method for producing a semi-insulating gallium arsenide single crystal according to claim 9, wherein the device for growing single crystals has one or more thermocouples outside in the radial direction of the crucible, and one or more positions of the thermocouple(s) can be moved in a direction parallel to the axial direction of the crucible. [11] Semi-insulating gallium arsenide single crystal substrate according to claim 2, wherein a carrier concentration in the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C in a Hall measurement according to the Van der Pauw method, 8.0 × 10 6 cm -3 or less Electron mobility of the semi-insulating gallium arsenide single-crystal substrate, measured at 25 °C in a Hall measurement using the Van der Pauw method, 4500 cm⁻¹ 2 / V·s or more an average value of a residual stress, as an absolute value of a difference between a stress along a radial direction of the first main surface and a stress along a tangential direction of the first main surface, 5.0 × 10 -6 or less an EL2 concentration of the semi-insulating gallium arsenide single-crystal substrate 7.5 × 10 15 / cm 3 or more and 1.0 × 10 16 cm -3 or less the semi-insulating gallium arsenide single-crystal substrate contains carbon and has an atomic concentration of carbon in the semi-insulating gallium arsenide single-crystal substrate of 5.0 × 10 15 cm -3 or more and 1.2 × 10 16 cm -3 or less.

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