Gallium arsenide single crystal substrate and method for its preparation

Abstract

A gallium arsenide single-crystal substrate having a circular principal face and a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, a fifth integrated intensity ratio, and a sixth integrated intensity ratio, wherein the third integrated intensity ratio is 1.05 or more and 1.2 or less, the fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are each 0.9 or more, and a ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or more and 1.3 or less, and a ratio of the fourth integrated intensity ratio to the first integrated intensity ratio,a ratio of the fifth integrated intensity ratio to the second integrated intensity ratio and a ratio of the sixth integrated intensity ratio to the third integrated intensity ratio is 0.7 or more and 1.1 or less.

Description

Technical field

[0001] The present disclosure relates to a gallium arsenide single crystal substrate and a process for its preparation. Background of the technology

[0002] Japanese Patent Publication No. 06-045318 (PTL 1) proposes a gallium arsenide single-crystal substrate (hereinafter also referred to as a "GaAs single-crystal substrate") with which thermal cleaning, i.e., the removal of an oxide layer, can be carried out at low temperature in a short time. Such a GaAs single-crystal substrate can be realized by artificially forming an arsenic-rich interfacial transition layer with a thickness of 3 Å or less on one of its surfaces. Japanese Patent Publication No. 2008-300747 (PTL 2) proposes providing a GaAs wafer that is cleaned by at least one surface of a GaAs single-crystal substrate with heat to such an extent that impurities and oxide on its surface can be removed by thermal cleaning. Citation list for patent literature PTL 1: Japanese patent publication no. 06-045318 PTL 2: Japanese patent publication 2008-300747 Summary of the invention

[0003] A gallium arsenide single-crystal substrate according to the present disclosure is a gallium arsenide single-crystal substrate having a major surface that is circular in shape. The gallium arsenide single-crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, a fifth integrated intensity ratio, and a sixth integrated intensity ratio.The first integrated intensity ratio and the fourth integrated intensity ratio are each determined by determining the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is applied under conditions of an X-ray incident energy of 600 eV on the center of the main surface and a photoelectron exit angle of 30°.Each of the second and fifth integrated intensity ratios is obtained by determining each of the spectra of the capture intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted to the outside of the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incidence energy of 600 eV and a photoelectron drop-off angle of 45°.The third and sixth integrated intensity ratios are each obtained by determining the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incidence energy of 600 eV and a photoelectron emission angle of 85°.The first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are each a ratio of a sum of an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of an arsenic element present as gallium arsenide, and an integrated intensity of an arsenic element present as metallic arsenic to a sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of a gallium element present as digallium trioxide, and an integrated intensity of a gallium element present as gallium arsenide.The fourth, fifth, and sixth integrated intensity ratios are each the ratio of the sum of the integrated intensity of arsenic as diarsenic pentoxide and the integrated intensity of arsenic as diarsenic trioxide to the sum of the integrated intensity of gallium as digallium monoxide and the integrated intensity of gallium as digallium trioxide. The third integrated intensity ratio is 1.05 or greater and 1.2 or less. The fourth, fifth, and sixth integrated intensity ratios are each 0.9 or greater. The ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or greater and 1.3 or less.The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are each 0.7 or more and 1.1 or less.

[0004] A process for producing a gallium arsenide single-crystal substrate according to the present disclosure is a process for producing a gallium arsenide single-crystal substrate having a major surface of circular shape. The process comprises: producing a gallium arsenide single-crystal substrate precursor having a circular shape; and obtaining the gallium arsenide single-crystal substrate from the gallium arsenide single-crystal substrate precursor. Obtaining the substrate comprises shaping the surface of the gallium arsenide single-crystal substrate precursor to a polished surface by polishing the surface, shaping the polished surface to an alkali-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid, and shaping the alkali-cleaned surface to an acid-cleaned surface by cleaning the alkali-cleaned surface by immersing the alkali-cleaned surface in a first acidic cleaning fluid.Containing 3 ppm by mass or more and 0.5% by mass or less of a first acid, and converting the acid-cleaned surface into a second acid-cleaned surface by cleaning the acid-cleaned surface by supplying a second acidic cleaning fluid containing 0.3 ppm by mass or more and 0.5% by mass or less of a second acid to the acid-cleaned surface at a flow rate of 0.1 l / minute or more and 5 l / minute or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more, and the second acid-cleaned surface is formed into the main surface by performing a heat treatment on the second acid-cleaned surface in an inert gas atmosphere for 1 minute or more and 30 minutes or less under atmospheric pressure and at temperatures of 150°C or more and 300°C or less. The first acid contained in the first acidic cleaning fluid is at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid.The second acid contained in the second acidic cleaning fluid is at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid and nitrous acid. Brief description of the drawings Fig. Figure 1 is an exemplary diagram showing a relationship between a measurement depth (horizontal axis) of a main surface of a GaAs single crystal substrate according to the present embodiment and a ratio (vertical axis) of an integrated intensity of the total amount of an arsenic element to an integrated intensity of the total amount of a gallium element and a ratio (vertical axis) of an integrated intensity of an arsenic element present as arsenic oxide to an integrated intensity of a gallium element present as gallium oxide. Fig.Figure 2 is an explanatory diagram that schematically shows the configuration of an analysis system using X-ray photoelectron spectroscopy (XPS). Fig. Figure 3A is a diagram showing an exemplary Ga3d spectrum after background correction, as obtained on the basis of XPS, where X-ray radiation is applied to the center of the main surface of the GaAs single crystal substrate according to the present embodiment. Fig. Figure 3B is a diagram showing an exemplary As3d spectrum after background correction, as obtained on the basis of XPS, where X-rays are directed at the center of the main surface of the GaAs single crystal substrate according to the present embodiment. Fig. Figure 4 is an explanatory diagram showing five measurement points on a GaAs single crystal substrate with a diameter of 75 mm or more and less than 150 mm in the present embodiment. Fig. Figure 5 is an explanatory diagram illustrating nine measurement points on a GaAs single crystal substrate with a diameter of 150 mm or more and 205 mm or less in the present embodiment. Fig. Figure 6 is a flowchart showing a process for producing the GaAs single crystal substrate according to the present embodiment. Detailed description [problem to be solved by the present disclosure]

[0005] One method used to evaluate the mirror surface property (i.e., the presence or absence of a height difference) of an epitaxial layer surface is turbidity, where an increase in the turbidity value is known to correlate with a decrease in the device property. Turbidity refers to the amount of scattered light that is scattered due to surface irregularities, fine defects, and foreign matter when laser light strikes the surface of the epitaxial layer. The turbidity is expressed as the ratio between the amount of scattered light and the amount of laser light incident on the surface. The turbidity is expressed in parts per million (ppm). It is assumed that the surface has a better mirror surface property and the height difference is smaller the lower the turbidity value.The height difference results from a stacking fault, which arises, for example, during the growth of an epitaxial layer on a GaAs single-crystal substrate. Since the stacking fault depends on the mirror surface properties of the main surface of the GaAs single-crystal substrate, it is necessary to create a GaAs single-crystal substrate with a main surface exhibiting high mirror properties in order to reduce the haze value. The thermal purification described above was expected to be one means of creating such a GaAs single-crystal substrate with a main surface exhibiting high mirror surface properties by removing an oxide layer on the main surface. In some cases, however, it is necessary to further reduce the haze value of the epitaxial layer grown on the main surface of the GaAs single-crystal substrate, which has been shaped into a mirror surface by thermal purification, as in PTL 1.

[0006] In view of the above, an objective of the present disclosure is to provide a gallium arsenide single-crystal substrate for improving a device property by achieving the formation of an epitaxial layer with a reduced turbidity value and a method for producing the gallium arsenide single-crystal substrate. [Beneficial effect of the present disclosure]

[0007] According to the present disclosure, it is possible to provide a gallium arsenide single crystal substrate to improve a device property by achieving the formation of an epitaxial layer with a reduced turbidity value, and a method for producing the gallium arsenide single crystal substrate. [Description of the embodiments]

[0008] First, an overview of one embodiment of the present disclosure is described. To solve the problem described above, the present inventors have completed the present disclosure as a result of careful study. That is, the present inventors have taken care to obtain a primary surface with a high mirror surface property in a gallium arsenide single-crystal substrate by carrying out a novel cleaning process on a gallium arsenide single-crystal substrate precursor with a circular surface, which was cut from a gallium arsenide single crystal. In particular, in addition to carrying out a conventionally known liquid-phase process, which includes both alkaline cleaning with an alkaline solution and acid cleaning with an acidic solution, cleaning with a second acid and heat treatment were carried out.As a result, it was found that in the GaAs single-crystal substrate obtained by the novel purification method described above, the oxide layer has a composition rich in arsenic, and also rich in digallium monoxide and diarsene trioxide, due to a reducing effect of metallic arsenic generated during the purification process. It was found that the oxide layer with this composition exhibits the property that the digallium monoxide and diarsene trioxide readily sublime and can therefore be effectively removed by thermal purification.In this way, the GaAs single-crystal substrate with the main surface having good mirror surface properties can be obtained to arrive at the GaAs single-crystal substrate on which an epitaxial layer with a reduced turbidity value can be formed, thereby completing the present disclosure.

[0009] Next, embodiments of the present disclosure will be listed and described.

[0010] A gallium arsenide single-crystal substrate according to an embodiment of the present disclosure is a gallium arsenide single-crystal substrate having a circular main surface. The gallium arsenide single-crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, a fifth integrated intensity ratio, and a sixth integrated intensity ratio.The first integrated intensity ratio and the fourth integrated intensity ratio are each obtained by determining the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed towards a center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°.The second and fifth integrated intensity ratios are each obtained by determining the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed towards the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 45°.The third and sixth integrated intensity ratios are each obtained by determining the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed towards the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°.The first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are each a ratio of a sum of an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of an arsenic element present as gallium arsenide, and an integrated intensity of an arsenic element present as metallarsene to a sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of a gallium element present as digallium trioxide, and an integrated intensity of a gallium element present as gallium arsenide.The fourth, fifth, and sixth integrated intensity ratios are each a ratio of the sum of the integrated intensity of arsenic (present as diarsenic pentoxide) and arsenic (present as diarsenic trioxide) to the sum of the integrated intensity of gallium (present as digallium monoxide) and gallium (present as digallium trioxide). The third integrated intensity ratio is 1.05 or greater and 1.2 or less. The fourth, fifth, and sixth integrated intensity ratios are each 0.9 or greater. The ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or greater and 1.3 or less.The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are each 0.7 or greater and 1.1 or less.

[0011] The gallium arsenide single crystal substrate with such a feature can have a main surface with a high mirror surface property, since an oxide layer can be effectively removed by thermal purification, allowing an epitaxial layer with a reduced turbidity value to be formed on it.

[0012] Preferably, the ratio of the first integrated intensity to the third integrated intensity is 0.95 or greater and 1.2 or less. This allows the oxide layer to be removed more effectively by thermal cleaning.

[0013] Preferably, the third integrated intensity ratio is 1.05 or higher and 1.1 or lower. This allows the oxide layer to be removed more effectively by thermal cleaning.

[0014] Preferably, the fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are 1.2 or less. This allows the oxide layer to be removed more effectively by thermal cleaning.

[0015] Preferably, the ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are 0.75 or more and 1.05 or less, respectively. This allows the oxide layer to be removed more effectively by thermal cleaning.

[0016] Preferably, the gallium arsenide single-crystal substrate has a diameter of 75 mm or more and 205 mm or less. Thus, the gallium arsenide single-crystal substrate with a diameter of 75 mm or more and 205 mm or less can be provided with a main surface exhibiting high mirror surface properties, allowing the formation of an epitaxial layer with a reduced turbidity value.

[0017] The gallium arsenide single-crystal substrate preferably has the following feature: The gallium arsenide single-crystal substrate has a diameter of 75 mm or more and less than 150 mm. The gallium arsenide single-crystal substrate has a seventh integrated intensity ratio, an eighth integrated intensity ratio, a ninth integrated intensity ratio, and a tenth integrated intensity ratio.The seventh and ninth integrated intensity ratios are each obtained by determining the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed to five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 30°.The eighth and tenth integrated intensity ratios are each obtained by determining the spectra of the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted from the gallium arsenide single crystal substrate, based on X-ray photoelectron spectroscopy, in which X-ray radiation is directed at each of the five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 85° at each of the five measurement points on the main surface.The seventh and eighth integrated intensity ratios are each a ratio of a sum of an integrated intensity of the arsenic element present as diarsene pentoxide, an integrated intensity of the arsenic element present as diarsene trioxide, an integrated intensity of the arsenic element present as gallium arsenide, and an integrated intensity of the arsenic element present as arsenic metal to a sum of an integrated intensity of the gallium element present as digallium monoxide, an integrated intensity of the gallium element present as digallium trioxide, and an integrated intensity of the gallium element present as gallium arsenide.The ninth and tenth integrated intensity ratios are each the ratio of the sum of the integrated intensity of arsenic (present as diarsene pentoxide) and arsenic (present as diarsene trioxide) to the sum of the integrated intensity of gallium (present as digallium monoxide) and gallium (present as digallium trioxide). A standard deviation and a mean value of the eighth integrated intensity ratio satisfy a relationship of standard deviation / mean value ≤ 0.01.A standard deviation and a mean value of R1 / R2 satisfy a relationship of standard deviation / mean value ≤ 0.07, where R1 / R2 is a ratio of a ratio R1 and a ratio R2, where the ratio R1 is a ratio of the ninth integrated intensity ratio to the seventh integrated intensity ratio, and the ratio R2 is a ratio of the tenth integrated intensity ratio to the eighth integrated intensity ratio. If the diameter is represented by D, and two axes, each passing through the center of the principal surface, lying on the principal surface and orthogonal to each other, are defined as the X-axis and Y-axis, the coordinates (X, Y) of the five measurement points on the X-axis and Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), and (0, -D / 4), respectively. The units of D and each of the X and Y coordinates (X, Y) are mm.Since the oxide layer is effectively removed by thermal purification in the gallium arsenide single crystal substrate with a diameter of 75 mm or more and less than 150 mm, it is possible to obtain a main surface with a high mirror surface property without deviation in the plane, so that an epitaxial layer with a reduced turbidity value can be formed on it.

[0018] The gallium arsenide single-crystal substrate preferably has the following feature. The gallium arsenide single-crystal substrate has a diameter of 150 mm or more and 205 mm or less. The gallium arsenide single-crystal substrate has an eleventh, a twelfth, a thirteenth, and a fourteenth integrated intensity ratio. The eleventh and thirteenth integrated intensity ratios are each obtained by determining the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single-crystal substrate based on X-ray photoelectron spectroscopy, in which X-rays are directed under conditions of an X-ray incidence energy of 600 eV and an emission angle of the photoelectrons of 30°.The twelfth and fourteenth integrated intensity ratios are each obtained by determining the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted from the gallium arsenide single-crystal substrate, respectively, using X-ray photoelectron spectroscopy. This involves directing X-ray radiation onto each of the nine measurement points on the main surface under conditions of an X-ray radiation energy of 600 eV and a photoelectron emission angle of 30°.The eleventh and twelfth integrated intensity ratios are each the ratio of the sum of an integrated intensity of the arsenic element present as diarsene pentoxide, an integrated intensity of the arsenic element present as diarsene trioxide, an integrated intensity of the arsenic element present as gallium arsenide, and an integrated intensity of the arsenic element present as metallarsene to a sum of an integrated intensity of the gallium element present as digallium monoxide, an integrated intensity of the gallium element present as digallium trioxide, and an integrated intensity of the gallium element present as gallium arsenide.Each of the thirteenth and fourteenth integrated intensity ratios is a ratio of the sum of the integrated intensity of arsenic as diarsene pentoxide and the integrated intensity of arsenic as diarsene trioxide to the sum of the integrated intensity of gallium as digallium monoxide and the integrated intensity of gallium as digallium trioxide. A standard deviation and a mean of the twelfth integrated intensity ratio satisfy a relationship of standard deviation / mean ≤ 0.015.A standard deviation and a mean value of R3 / R4 satisfy a relationship of standard deviation / mean value ≤ 0.078, where R3 / R4 is a ratio of a ratio R3 and a ratio R4, where the ratio R3 is a ratio of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio and the ratio R4 is a ratio of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio. If the diameter is represented by D and two axes, each passing through the center of the main surface, each lying on the main surface and being orthogonal to each other, are defined as the X-axis and Y-axis, then the coordinates (X, Y) of the nine measurement points on the X-axis and Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), (0, -D / 4), (D / 2-10, 0), (0, D / 2-10), (-(D / 2-10), 0) and (0, -(D / 2-10)).The units of D and each of the X and Y in the coordinates (X, Y) are mm. By effectively removing the oxide layer by thermal purification on the gallium arsenide single-crystal substrate with a diameter of 150 mm or more and 205 mm or less, the main surface can be obtained with a high mirror surface property without deviations in the plane, thereby forming an epitaxial layer with a reduced turbidity value.

[0019] Preferably, the gallium arsenide single-crystal substrate has an epitaxial layer arranged on its main surface, with a maximum turbidity value of 350 ppm or less and an average turbidity value of 2.5 ppm or less. Thus, it is possible to provide the gallium arsenide single-crystal substrate having a main surface on which the epitaxial layer exhibits a reduced turbidity value.

[0020] A method for producing a gallium arsenide single-crystal substrate according to an embodiment of the present disclosure is a method for producing a gallium arsenide single-crystal substrate having a circular principal surface. The method comprises: producing a gallium arsenide single-crystal substrate precursor having a circular surface; and obtaining the gallium arsenide single-crystal substrate from the gallium arsenide single-crystal substrate precursor. Obtaining the substrate comprises: forming the surface of the gallium arsenide single-crystal substrate precursor into a polished surface by polishing the surface; forming the polished surface into an alkali-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid.Forming the alkali-cleaned surface into an acid-cleaned surface by cleaning the alkali-cleaned surface by immersing the alkali-cleaned surface in a first acid cleaning fluid containing 0.3 ppm or more by mass and 0.5% or less by mass of a first acid; forming the acid-cleaned surface into a second acid-cleaned surface by cleaning the acid-cleaned surface by supplying a second acid cleaning fluid containing 0.3 ppm or more by mass and 0.5% or less by mass of a second acid at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more;and forming the second acid-cleaned surface into the main surface by performing a heat treatment on the second acid-cleaned surface in an inert gas atmosphere for 1 minute or longer and 30 minutes or less under atmospheric pressure and at temperatures of 150 °C or more and 300 °C or less. The first acid contained in the first acid cleaning liquid is at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid. The second acid contained in the second acid cleaning liquid is at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid. By the manufacturing process with such a feature, it is possible to obtain a gallium arsenide single-crystal substrate with a main surface exhibiting an oxide layer that can be effectively removed by thermal cleaning.

[0021] Preferably, the method includes forming an epitaxial layer on the main surface. This allows an epitaxial layer with a reduced turbidity value to be formed on the main surface. [Description of the embodiments]

[0022] In the following, an embodiment (hereinafter also referred to as "the present embodiment") according to the present disclosure is described in more detail, although the present disclosure is not limited to it. Although the explanations in the following description are made with reference to figures, identical or corresponding elements in the present description and the figures are designated by the same reference numerals, and the corresponding explanations are not repeated. Furthermore, in each of the figures, the scale of the individual components is adjusted accordingly for better understanding, and the scale of the individual components in the figures does not necessarily correspond to the actual scale of the components.

[0023] In this description, the expression "A to B" denotes a range from lower to upper limits (i.e., A or more and B or less), and where no unit is specified for A and only a unit is specified for B, the unit of A is the same as the unit of B. Where a compound or the like is expressed in this description by a chemical formula and an atomic ratio is not specifically restricted, it is understood that all conventionally known atomic ratios are included, and the atomic ratio should not necessarily be restricted to one in the stoichiometric range.

[0024] In this description, the term "main face" of a gallium arsenide single-crystal substrate refers to each of the two circular faces of the substrate. If at least one of the two faces satisfies the scope of the claims relating to this disclosure in the gallium arsenide single-crystal substrate, the gallium arsenide single-crystal substrate falls within the scope of the present invention. An epitaxial layer may be arranged on the "main face" of the gallium arsenide single-crystal substrate. Furthermore, in this description, the term "plane" in the expressions "in plane" or "in the plane" means the "main face". When the diameter of the gallium arsenide single-crystal substrate is specified as "75 mm", this means that the diameter is approximately 75 mm (about 75 to 76.5 mm) or 3 inches. When the diameter is specified as "100 mm", this means that the diameter is approximately 100 mm (about 95 to 105 mm) or 4 inches.If the diameter is specified as "150 mm," this means that the diameter is approximately 150 mm (about 145 to 155 mm) or 6 inches. If the diameter is specified as "200 mm," this means that the diameter is approximately 200 mm (about 195 to 205 mm) or 8 inches. It should be noted that the diameter can be measured with a standard outside diameter measuring tool, such as a caliper.

[0025] With regard to crystallographic information in this description, a single orientation is represented by [], a group orientation by <>, a single plane by (), and a group plane by {}. Furthermore, a negative crystallographic index is normally expressed by a '-' (line) above a number, but in this description by a negative sign before the number. [Gallium arsenide single crystal substrate]

[0026] A gallium arsenide single-crystal substrate (GaAs single-crystal substrate) according to the present embodiment is a GaAs single-crystal substrate with a major surface having a circular shape. The GaAs single-crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, a fifth integrated intensity ratio, and a sixth integrated intensity ratio.The first integrated intensity ratio and the fourth integrated intensity ratio are each obtained by determining the spectra of the detection intensities of 3d electrons of gallium (Ga) and arsenic (As) with respect to the binding energy of a photoelectron emitted outwards from the GaAs single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is applied under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 30°.The second and fifth integrated intensity ratios are obtained by determining each of the spectra of the detection intensities of 3d electrons of Ga and As with respect to the binding energy of a photoelectron emitted outwards from the GaAs single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 45°.The third and sixth integrated intensity ratios are obtained by determining each of the spectra of the detection intensities of the 3d electrons of Ga and As with respect to the binding energy of a photoelectron emitted outwards from the GaAs single crystal substrate, based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to the center of the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 85°.

[0027] The first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are ratios of the sum of the integrated intensities of an As element (hereinafter referred to as "As" for simplicity). s+“ denoted), which exists as diarsene pentoxide (As2O5), an integrated intensity of an As element (hereinafter also referred to as “As” for simplicity). 3+ “ (hereinafter referred to as diarsenic trioxide (As2O3) for the sake of simplicity), an integrated intensity of an As element (hereinafter also referred to as “As-Ga”) present as gallium arsenide (GaAs), and an integrated intensity of an As element (hereinafter also referred to as “metal As”) in the form of metal arsenic (metal As) to a sum of an integrated intensity of a Ga element (hereinafter also referred to as “Ga*”) present as digallium monoxide (Ga2O), an integrated intensity of a Ga element (hereinafter also referred to as “Ga” for the sake of simplicity) 3+“ (referred to for simplicity) as digallium trioxide (Ga₂O₃) and an integrated intensity of a Ga element (hereinafter also referred to as “Ga-As” for simplicity) as gallium arsenide (GaAs). The fourth, fifth, and sixth integrated intensity ratios are ratios of the sum of the integrated intensities of the As element (As). 5+ ), which exists as As2O5, and an integrated intensity of the As element (As 3+ ), which exists as As2O3, to a sum of an integrated intensity of the Ga element (Ga + ), which exists as Ga2O, and an integrated intensity of the Ga element (Ga 3+), which exists as Ga₂O₃. In the GaAs single-crystal substrate, the third integrated intensity ratio is 1.05 or greater and 1.2 or less. Each of the fourth, fifth, and sixth integrated intensity ratios is 0.9 or greater. The ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or greater and 1.3 or less. The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are each 0.7 or greater and 1.1 or less.

[0028] The first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are each a ratio of the sum of an integrated intensity of an As element present as diarsene pentoxide (As2O5) (hereinafter also referred to as "As" for simplicity). s+ “designated), an integrated intensity of an As element present as diarsenic trioxide (As2O3) (hereinafter also referred to as “As” for simplicity). 3+ “ denoted), an integrated intensity of an As element present as gallium arsenide (GaAs) (hereinafter also referred to as “As-Ga” for simplicity) and an integrated intensity of an As element present in the form of metal arsenic (metal-As) (hereinafter also referred to as “metal-As” for simplicity) to a sum of an integrated intensity of a Ga element present as digallium monoxide (Ga2O) (hereinafter also referred to as “Ga” for simplicity). +“ denoted), an integrated intensity of a Ga element present as digallium trioxide (Ga2O3) (hereinafter also referred to as “Ga” for simplicity). 3+ “ denoted) and an integrated intensity of a Ga element present as gallium arsenide (GaAs) (hereinafter also referred to as “Ga-As” for simplicity). The fourth, fifth, and sixth integrated intensity ratios are ratios of the sum of the integrated intensities of the As element present as As₂O₅ (As₂O₅). 5+ ) and an integrated intensity of the As element present as As2O3 (As 3+ ) to a sum of an integrated intensity of the Ga element present as Ga2O (Ga + ) and an integrated intensity of the Ga element present as Ga2O3 (Ga 3+In the GaAs single-crystal substrate, the third integrated intensity ratio is 1.05 or greater and 1.2 or less. The fourth, fifth, and sixth integrated intensity ratios are each 0.9 or greater. The ratio of the first integrated intensity to the third integrated intensity is 0.9 or greater and 1.3 or less. The ratio of the fourth integrated intensity to the first integrated intensity, the ratio of the fifth integrated intensity to the second integrated intensity, and the ratio of the sixth integrated intensity to the third integrated intensity are each 0.7 or greater and 1.1 or less.

[0029] An oxide layer can be effectively removed from a GaAs single-crystal substrate with this property by thermal purification, allowing the GaAs single-crystal substrate to exhibit a major surface with a high mirror-like surface quality. Therefore, an epitaxial layer with a reduced turbidity value can be formed on the GaAs single-crystal substrate. <Hauptfläche>

[0030] The GaAs single-crystal substrate has a principal surface with the circular shape described above. In this description, the "circular shape" representing the shape of the principal surface includes not only a geometric circle but also a shape where the principal surface does not form a geometric circle due to the formation of at least one notch, one orientation flattening (hereinafter also referred to as "OF"), and one index flattening (hereinafter also referred to as "IF"). That is, the "shape when the principal surface does not form a geometric circle" means a shape where the length of a line segment extending from any point on the notch, OF, and IF to the center of the principal surface is shorter than the line segments extending from any point on the outer circumference of the principal surface to the center of the principal surface.In other words, in the present description, the principal surface is referred to as a "circular shape" based on its pre-notch shape, OF, and IF. Therefore, the position of the principal surface's center point and the size (length) of the substrate's diameter are determined based on this pre-notch circular shape, OF, IF, and so on. It should be noted that the "shape when the principal surface is not a geometric circle" also includes a shape where the lengths of all line segments extending from any point on the principal surface's outer circumference to its center point are not necessarily equal due to the pre-notch shape of the GaAs single crystal substrate.In this case, the center of the main surface refers to the position of the center of gravity, and the diameter of the substrate refers to the length of the longest line segment among the line segments that extend from one point on the outer circumference of the substrate, through the center of the main surface, to another point on the outer circumference of the substrate. < X-ray photoelectron spectroscopy (XPS) using synchrotron radiation >

[0031] In developing the GaAs single-crystal substrate on which an epitaxial layer with reduced turbidity can be formed, the inventors focused on X-ray photoelectron spectroscopy (XPS) using synchrotron radiation, which allows for high-precision analysis of the condition of the main surface of the GaAs single-crystal substrate. Specifically, the XPS was performed using synchrotron radiation to identify and eliminate a cause for the deterioration of the mirror surface properties of the main surface of the GaAs single-crystal substrate, thus enabling the formation of a GaAs single-crystal substrate on which an epitaxial layer with reduced turbidity can be formed.Here, XPS refers to an analytical method in which X-rays are directed at a sample and the kinetic energy distribution of the photoelectrons emitted from the sample is measured in order to gain insights into the type, abundance, chemical bonding states, and the like of the elements present on the surface of the sample.

[0032] When the main surface of a GaAs single-crystal substrate is analyzed using XPS, the analysis is typically performed with X-rays with an energy of approximately 1.487 keV. However, when using X-rays with an incident energy of approximately 1.487 keV and an exit angle of 30°, information about the state of the main surface of the GaAs single-crystal substrate is obtained as an average value over a region extending from the main surface to a depth of approximately 5 nm. This region corresponds to roughly 20 atomic layers. Therefore, it is difficult to analyze the state of the main surface of the GaAs single-crystal substrate with high precision using XPS.If the X-ray radiation with a fixed incidence energy of about 1.4 keV is used and the photoelectron lift-off angle in the XPS is angled in such a way as to obtain information about the state of the main surface of the GaAs single crystal substrate, a measurement error with respect to the angle becomes too large and, due to the low ionization efficiency of the photoelectron intensity, a large measurement error also arises, making a highly precise analysis difficult.

[0033] On the other hand, in the present disclosure, since the XPS is carried out under conditions in which X-rays with an X-ray incidence energy of 600 eV are used and the exit angle of the photoelectrons is set to 30°, 45° or 85° as described above, the state of the main surface of the GaAs single crystal substrate can be analyzed.

[0034] When the X-ray incidence energy is set to 600 eV and the photoelectron exit angle to 30° as conditions for performing XPS, the state of the main surface of the GaAs single-crystal substrate can be determined as an average state over a region from the main surface to a depth of approximately 2.25 nm. When the X-ray incidence energy is set to 600 eV and the photoelectron exit angle to 45° as conditions for XPS, information about the state of the main surface of the GaAs single-crystal substrate is obtained as an average value over a region from the main surface to a depth of approximately 3.18 nm.When the X-ray incidence energy is set to 600 eV and the photoelectron exit angle to 85° as conditions for performing XPS, knowledge of the state of the main surface of the GaAs single-crystal substrate can be obtained as an average state in a region from the main surface to a depth of approximately 4.48 nm. This means that the region from the main surface of the GaAs single-crystal substrate to a depth of approximately 5 nm (corresponding to about 20 atomic layers) can be analyzed in detail for approximately every first to third atomic layer, thus allowing for a more accurate analysis of the main surface state than is possible with prior art methods.

[0035] It is known that after a cleaning step, an oxide layer approximately 1 to 2 nm thick forms on the main surface of the GaAs single-crystal substrate. Therefore, attempts were made to form an epitaxial layer on the main surface after removing the oxide by thermal cleaning in order to reduce the haze value of the epitaxial layer's surface. However, even after thermal cleaning, some of the oxide layer remains on the main surface, resulting in a relatively high haze value of the epitaxial layer's surface. To solve this problem, the inventors took care to use synchrotron radiation to selectively treat the environment of an interface (i.e., the surface of the epitaxial layer) with the help of the XPS described above.the region at a depth of approximately 2 to 5 nm from the main surface of the GaAs single-crystal substrate) between the oxide layer covering the top surface of the main surface of the GaAs single-crystal substrate and a layer (hereinafter also referred to as the "main layer" of the GaAs single-crystal substrate) consisting of gallium (Ga) and arsenic (As) located directly beneath the oxide layer. As a result, the inventors found that if the oxide layer has an As-rich composition and the GaAs single-crystal substrate also has an As₂O₃-rich composition, the oxide layer is effectively removed by thermal purification because the oxide layer has the property of being readily sublimed. In particular, it was also found that if the metal As is generated near the interface described above, the generation of Ga₂O and As₂O₃ in the oxide layer is promoted by a reducing effect of the As.This means that the inventors considered controlling the compositions of arsenic and oxide in the oxide layer in such a way as to obtain a main surface with high mirror surface properties. It should be noted that in this description, the "surface" of the oxide layer refers to the surface of the oxide layer facing the GaAs single-crystal substrate. <Erstes integriertes Intensitätsverhältnis, zweites integriertes Intensitätsverhältnis, drittes integriertes Intensitätsverhältnis, viertes integriertes Intensitätsverhältnis, fünftes integriertes Intensitätsverhältnis und sechstes integriertes Intensitätsverhältnis>

[0036] The GaAs single-crystal substrate according to the present embodiment has the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio. The first and fourth integrated intensity ratios are each obtained by determining the detection intensities of the 3d electrons of Ga and As with respect to the binding energy of the photoelectrons emitted outwards from the GaAs single-crystal substrate using X-ray photoelectron spectroscopy, in which X-rays are directed towards the center of the main surface under conditions of an X-ray incidence energy of 600 eV and an exit angle of the photoelectrons of 30°.The second integrated intensity ratio and the fifth integrated intensity ratio are obtained by determining each of the spectra of the detection intensities of the 3d electrons of Ga and As with respect to the binding energy of the photoelectron emitted outwards from the GaAs single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed towards the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 45°.The third and sixth integrated intensity ratios are each obtained by determining the detection intensities of the 3d electrons of Ga and As with respect to the binding energy of the photoelectron emitted outwards from the GaAs single crystal substrate using X-ray photoelectron spectroscopy, in which X-ray radiation is directed towards the center of the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 85° to the center of the main surface.

[0037] The first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are each the ratio of the sum of the integrated intensities of the As element present as As2O5 (As 5+ ), the integrated intensity of the As element present as As2O3 (As 3+), the integrated intensity of the As element present as GaAs (As-Ga), and the integrated intensity of the As element present as metal-As (Metal-As) to the sum of the integrated intensity of the Ga element present as Ga2O (Ga + ), the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ ), and the integrated intensity of the Ga element present as GaAs (Ga-As). The fourth, fifth, and sixth integrated intensity ratios are each the ratio of the sum of the integrated intensities of the As element present as As₂O₅ (As₂O₅). 5+ ), and the integrated intensity of the As element present as As2O3 (As 3+ ) to the sum of the integrated intensity of the Ga element present as Ga2O (Ga + ) and the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ ).

[0038] If the first integrated intensity ratio and the fourth integrated intensity ratio are represented by In1 and In4 respectively under the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, the fifth integrated intensity ratio and the sixth integrated intensity ratio, In1 and In4 can be expressed by the following mathematical formulas. In1=I(As2O5)+I(As2O3)+I(As_Ga)+I(As)I(Ga2O)+I(Ga2O3)+I(Ga_As)In4=I(As2O5)+I(As2O3)I(Ga2O)+I(Ga2O3)

[0039] On a GaAs single-crystal substrate, the third integrated intensity ratio is 1.05 or greater and 1.2 or less. The fourth, fifth, and sixth integrated intensity ratios are each 0.9 or greater. The ratio of the first to the third integrated intensity ratio is 0.9 or greater and 1.3 or less. The ratio of the fourth to the first integrated intensity ratio, the ratio of the fifth to the second integrated intensity ratio, and the ratio of the sixth to the third integrated intensity ratio are each 0.7 or greater and 1.1 or less.

[0040] Fig.Figure 1 is an exemplary diagram showing a relationship between a measurement depth (horizontal axis) from the main surface of the GaAs single-crystal substrate according to the present embodiment and each of the ratios (vertical axis) of the integrated intensity of the total amount of arsenic to the integrated intensity of the total amount of gallium and the ratio (vertical axis) of the integrated intensity of the arsenic present as arsenic oxide to the integrated intensity of the gallium. Fig.A point marked by a circle around a measurement depth (horizontal axis) of approximately 2.25 nm corresponds to the first integrated intensity ratio; a point marked by a circle around a measurement depth (horizontal axis) of approximately 3.18 nm to the second integrated intensity ratio; and a point marked by a circle around a measurement depth (horizontal axis) of approximately 4.48 nm to the third integrated intensity ratio. A point marked by a rectangle around a measurement depth (horizontal axis) of approximately 2.25 nm corresponds to the fourth integrated intensity ratio; a point marked by a rectangle around a measurement depth (horizontal axis) of approximately 3.18 nm corresponds to the fifth integrated intensity ratio; and a point marked by a rectangle around a measurement depth (horizontal axis) of approximately 4.48 nm corresponds to the sixth integrated intensity ratio. Fig. 1 means “Total Ga”, the sum of the integrated intensity of Ga + , the integrated intensity of Ga 3+ and the integrated intensity of Ga-As. “Total-As” refers to the sum of the integrated intensities of As. 5+ , the integrated intensity of As 3+ , the integrated intensity of As-Ga and the integrated intensity of metallic As. “Ga-O” denotes the sum of the integrated intensity of Ga + and the integrated intensity of Ga 3+ “As-O” denotes the sum of the integrated intensities of As 5+ and the integrated intensity of As 3+ .

[0041] In Fig.The first, second, and third integrated intensity ratios are 1.24, 1.24, and 1.16, respectively. The fourth, fifth, and sixth integrated intensity ratios are 1.14, 1.1, and 1.06, respectively. The fourth, fifth, and sixth integrated intensity ratios are each 0.9 or higher. The ratio of the first integrated intensity ratio to the third integrated intensity ratio is 1.07. The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio is 0.92. The ratio of the fifth integrated intensity ratio to the second integrated intensity ratio is 0.89.The ratio of the sixth integrated intensity ratio to the third integrated intensity ratio is 0.91. The ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and the ratio of the sixth integrated intensity ratio to the third integrated intensity ratio are each 0.7 or more and 1.1 or less.

[0042] Such a relationship means that the oxide layer, which extends to a depth of about 1 to 2 nm from the main surface, has an overall composition rich in arsenic, and a composition that is richer in arsenic oxide from an interface (about 2 to 5 nm deep from the main surface) between the main layer and the oxide layer to the surface of the oxide layer. Specifically, this means that since the third integrated intensity ratio is 1.05 or greater and 1.2 or less, arsenic is present in sufficient quantity for use throughout the oxide layer. This means that since the fourth, fifth, and sixth integrated intensity ratios are each 0.9 or greater, arsenic oxide is present in sufficient quantity at the interface between the main layer and the oxide layer, within the oxide layer, and at the surface of the oxide layer for use.This means that, since the ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or more and 1.3 or less, the composition is richer in arsenic from the interface between the main layer and the oxide layer towards the surface of the oxide film. Furthermore, this means that, since the ratio of the fourth integrated intensity ratio to the first, the fifth integrated intensity ratio to the second, and the sixth integrated intensity ratio to the third are each 0.7 or more and 11 or less, the arsenic oxide is sufficiently present throughout the entire oxide layer in the thickness direction for use, and the ratio of metallic arsenic to the oxide layer is therefore excellent.Since the oxide layer in this case is rich in Ga₂O and As₂O₃, which readily sublime, it can be assumed that the oxide layer can be effectively removed by thermal cleaning. Therefore, if, after thermal cleaning according to the present embodiment, an epitaxial layer has grown on the main surface of the GaAs single-crystal substrate, both the maximum and average haze values ​​of a surface of the epitaxial layer can be lower than in conventional techniques (for example, the maximum haze of the surface of the epitaxial layer can be 350 ppm or less, and the average haze can be 2.5 ppm or less). In this description, the term "surface" of the epitaxial layer refers to a surface of the epitaxial layer that faces the GaAs single-crystal substrate.

[0043] Such a relationship means that the oxide layer, which extends to a depth of about 1 to 2 nm from the main surface, has an overall composition rich in arsenic, and a composition that is richer in arsenic oxide from an interface (about 2 to 5 nm deep from the main surface) between the main layer and the oxide layer to the surface of the oxide layer. Specifically, this means that since the third integrated intensity ratio is 1.05 or greater and 1.2 or less, arsenic is present in sufficient quantity for use throughout the oxide layer. This means that since the fourth, fifth, and sixth integrated intensity ratios are each 0.9 or greater, arsenic oxide is present in sufficient quantity for use at the interface between the main layer and the oxide layer, within the oxide layer, and at the surface of the oxide layer.This means that, since the ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or more and 1.3 or less, the composition is richer in arsenic from the interface between the main layer and the oxide layer towards the surface of the oxide layer. Furthermore, this means that, since the ratio of the fourth integrated intensity ratio to the first, the fifth integrated intensity ratio to the second, and the sixth integrated intensity ratio to the third is each 0.7 or more and 1.1 or less, the arsenic oxide is sufficiently present throughout the oxide layer in the thickness direction for use, and the ratio of metal arsenic to oxide layer is therefore excellent.In this case, the oxide layer can be effectively removed by thermal purification because the oxide layer is rich in Ga₂O and As₂O₃, which sublime readily. Therefore, if an epitaxial layer has grown on the main surface of the GaAs single-crystal substrate after thermal purification according to the present embodiment, both the maximum and average haze values ​​of a surface of the epitaxial layer can be lower than in conventional techniques (for example, the maximum haze of the surface of the epitaxial layer can be 350 ppm or less, and the average haze can be 2.5 ppm or less). In this description, the term "surface" of the epitaxial layer refers to a surface of the epitaxial layer that faces the GaAs single-crystal substrate.

[0044] On the other hand, if the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, the fifth integrated intensity ratio and the sixth integrated intensity ratio are each obtained by performing XPS on the conventional GaAs single crystal substrate, one of the following relationships is not satisfied.This means that a condition that the third integrated intensity ratio is 1.05 or more and 1.2 or less is not met; a condition that at least one of the fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio is 0.9 or more is not met; a condition that a ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or more and 1.3 or less is not met; or a condition that at least one of the ratios of the fourth integrated intensity ratio to the first integrated intensity ratio, the fifth integrated intensity ratio to the second integrated intensity ratio, and the sixth integrated intensity ratio to the third integrated intensity ratio is 0.7 or more and 1.1 or less is not met.In such a GaAs single-crystal substrate, part of the oxide layer can remain on the main surface even after thermal purification. Therefore, if an epitaxial layer forms on the main surface of the GaAs single-crystal substrate after thermal purification, a height difference arises on the surface, which can lead to high maximum and average turbidity values.

[0045] As described above, the inventors first determined that the turbidity of the surface of the epitaxial layer formed on the main surface of the GaAs single-crystal substrate depends on the amount of arsenic, arsenic oxide, and gallium oxide in each of the oxide layers (area extending from the main surface to a depth of about 1 to 2 nm) and the area surrounding the interface (area at a depth of 2 to 5 nm from the main surface) between the oxide layer and the main layer.

[0046] Here, the ratio of the first integrated intensity to the third integrated intensity is preferably 0.95 or more and 1.2 or less. This optimizes the uniformity of the arsenic content in the oxide layer, allowing the oxide layer to be removed more effectively by thermal cleaning.

[0047] The third integrated intensity ratio is preferably 1.05 or higher and 1.1 or lower. This promotes the optimization of the arsenic content, which in turn allows the oxide layer to be removed more effectively by thermal cleaning.

[0048] Preferably, the fourth, fifth, and sixth integrated intensity ratios are 1.2 or less. This ensures that the arsenic oxide content in the oxide layer is sufficient to allow for more effective removal of the oxide layer by thermal cleaning.

[0049] Preferably, the fourth, fifth, and sixth integrated intensity ratios are 1.2 or less. This ensures that the arsenic oxide content in the oxide layer is sufficient and appropriate, allowing for more effective removal of the oxide layer by thermal cleaning.

[0050] Preferably, the ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the fifth integrated intensity ratio to the second integrated intensity ratio, and the sixth integrated intensity ratio to the third integrated intensity ratio is 0.75 or more and 1.05 or less, respectively. This prevents the amount of metal arsenic in the oxide layer from becoming too high, allowing the oxide layer to be removed more effectively by thermal cleaning. <durchmesser>

[0051] The GaAs single-crystal substrate preferably has a diameter of 75 mm or more and 205 mm or less. In other words, the diameter of the GaAs single-crystal substrate is preferably 3 to 8 inches. Thus, in the GaAs single-crystal substrate with a diameter of 75 mm or more and 205 mm or less, the main surface with the high mirror surface property can be obtained by removing the oxide layer by thermal refining. Here, with regard to the diameter, even if the substrate does not have a geometric circular shape due to the influence of OF, IF, or the like, the size (the diameter) of the substrate is determined under the assumption that the substrate has a circular shape before the formation of OF, IF, or the like. The GaAs single-crystal substrate preferably has a diameter of 100 mm or more and 205 mm or less, and also preferably has a diameter of 150 mm or more and 205 mm or less. <Verfahren zur Analyse eines GaAs-Einkristallsubstrats mittels Röntgen-Photoelektronenspektroskopie (XPS) unter Verwendung von Synchrotronstrahlung>

[0052] The following describes in more detail the method for analyzing the GaAs single crystal substrate using XPS with synchrotron radiation. (Analysis system)

[0053] Fig. Figure 2 is a schematic representation illustrating a configuration of an analysis system using X-ray photoelectron spectroscopy. As shown in Fig. As shown in Figure 2, an analysis system 100 comprises an X-ray source 10, a vacuum chamber 20, and an electron spectrometer 30. The X-ray source 10, the vacuum chamber 20, and the electron spectrometer 30 are connected in this order. The interior of the X-ray source 10, the vacuum chamber 20, and the electron spectrometer 30 is maintained in ultra-high vacuum. The pressure inside the X-ray source 10, the vacuum chamber 20, and the electron spectrometer 30 is, for example, 4 × 10⁻⁶. -7 Pa.

[0054] The X-ray source 10 generates X-rays, which are referred to as synchrotron radiation. For example, the beamline "BL17" in the SAGA light source can be used as the X-ray source 10.

[0055] The X-ray generating device 10 can generate X-rays with any energy in the range of 50 to 2000 eV in the “BL17” to direct the X-rays onto the GaAs single-crystal substrate 1 arranged in a vacuum container 20. The in Fig. The X-ray generating device 10 shown in Figure 2 comprises an X-ray source 11, slots 12, 14, and a grating 13. The slots 12, 14 are arranged on the upstream and downstream sides, respectively, with respect to the grating (spectrometer) 13. Each of the slots 12, 14 is, for example, a four-quadrant slot.

[0056] By deflecting the direction of motion of high-energy electrons by means of a magnetic field generated by a deflection magnet in a circular accelerator, the X-ray source 11 emits synchrotron radiation (X-rays) that is emitted in a direction tangential to the direction of motion.

[0057] The X-rays emitted by X-ray source 11 have a high luminance. In particular, the number of photons emitted by X-ray source 11 per second is 10 9 Photons / s. However, the luminance (intensity) of the X-rays emitted by X-ray source 11 decreases over time. For example, the luminance of the X-rays emitted 11 hours after activation of X-ray source 11 is 1 / 3 of the luminance of the X-rays emitted immediately after its activation.

[0058] The X-rays emitted by the X-ray source 11 are collimated by a collimating mirror (not shown) or the like. The slot 12 allows a portion of the collimated X-rays to pass through. The X-rays passing through the slot 12 are monochromatized by the grating 13. The slot 14 limits the width of the monochromatized X-rays.

[0059] The energy of the X-rays emitted by the X-ray source 10 is determined by the slot widths of slots 12 and 14 and the line density of the grating 13. For example, X-rays with an energy of 600 eV are emitted by the X-ray source 10 by adjusting the emission angle in the grating using grating 13, where the slot width of slots 12 and 14 is 30 µm and the line density in the center is 400 I / mm.

[0060] When the X-ray radiation from the X-ray generating device 10 hits the GaAs single crystal substrate 1 placed in the vacuum container 20, photoelectrons are emitted from the GaAs single crystal substrate 1.

[0061] The electron spectrometer 30 measures the kinetic energy distribution of the photoelectrons emitted by the GaAs single-crystal substrate 1. The electron spectrometer 30 has a hemispherical analyzer and a detector. The hemispherical analyzer separates the photoelectrons. The detector counts the number of photoelectrons of each energy.

[0062] An angle θ1, formed by the direction of motion of the X-rays incident on the GaAs single-crystal substrate 1 from the X-ray generator 10 and the main area 1m² of the GaAs single-crystal substrate 1, is variable. Furthermore, an angle (hereinafter referred to as the "emission angle θ2"), formed by the direction of propagation of the photoelectrons detected by the electron spectrometer 30 under the photoelectrons emitted by the GaAs single-crystal substrate 1 and the main area 1m² of the GaAs single-crystal substrate 1, is also variable. In the present embodiment, the emission angle θ2 is set to 30°, 45°, or 85°. The angle θ1 is not specifically limited but is, for example, set to 85°.

[0063] For example, a high-resolution XPS analyzer “R3000” from Scienta Omicron can be used as an electron spectrometer 30. (Depth of the main surface for analysis)

[0064] Some of the photoelectrons emitted from the GaAs single-crystal substrate 1 in response to the application of X-rays lose energy due to inelastic scattering. Therefore, only a portion of the photoelectrons generated in the GaAs single-crystal substrate 1 escape into the vacuum and reach the electron spectrometer 30, retaining the energy they possessed at their generation. The photoelectrons emitted from the surface are generated at a depth approximately three times the inelastic mean free path (IMFP) of the photoelectrons. Thus, the depth d (nm) from the main surface of the GaAs single-crystal substrate to be analyzed is expressed by the following mathematical formula. In this formula, λ (nm) represents the IMFP value and θ2 represents the emission angle. d=3λ sin θ2

[0065] As stated in “Method of Estimating Inelastic Mean Free Path of Electrons by Tpp-2M Formula”, Journal of Surface Analysis, Volume 1, No. 2, 1995, λ (Å) is represented by the following mathematical formulas. λ=EEp2[β ln(γE)−C / E+D / E2] Ep=28.8(NvρAw)1 / 2 β=−0.10+0.944(Ep2+Eg2)12+0.069ρ0.1 γ=0.191ρ−0.50 C=1.97−0.94U D=53.4−20.8U U=NvρAw=Ep2829.4

[0066] In each of the mathematical formulas mentioned above, A W for atomic weight or molecular weight, N v for the number of valence electrons per atom or molecule, E p for the plasmon energy (eV) of the free electron, ρ for the density (g / cm³) 3 ) and E g for the band gap energy (eV). E stands for the kinetic energy (eV) of the photoelectrons and is calculated from the energy (eV) of the applied X-ray radiation and the binding energy (eV) between the electron and the atomic nucleus.

[0067] The depth d (nm) of the main surface of the GaAs single-crystal substrate to be analyzed can be determined using any of the mathematical formulas above. That is, the depth d (nm) of the main surface of the GaAs single-crystal substrate is calculated using each of the above mathematical formulas, different parameter values ​​for the 3d electrons of the Ga and As elements, and the X-ray energy (600 eV). The depth d (nm) is obtained as follows.

[0068] If the X-ray incident energy is 600 eV and the photoelectron exit angle is 30°, the depth d is approximately 2.25 nm. If the X-ray incident energy is 600 eV and the photoelectron exit angle is 45°, the depth d is approximately 3.18 nm. If the X-ray incident energy is 600 eV and the photoelectron exit angle is 85°, the depth d is approximately 4.48 nm.

[0069] (Method for calculating the first integrated intensity ratio, the second integrated intensity ratio, the third integrated intensity ratio, the fourth integrated intensity ratio, the fifth integrated intensity ratio and the sixth integrated intensity ratio)

[0070] Regarding a method for calculating each of the first, second, third, fourth, fifth, and sixth integrated intensity ratios in the main surface based on the XPS described above, a method for calculating each of the first and fourth integrated intensity ratios is described below. In this case, the XPS is performed on the center of the main surface of the GaAs single-crystal substrate using X-rays with an energy of 600 eV. The emission angle of the photoelectrons is 30°. Thus, the kinetic energy distribution of the photoelectrons emitted by the GaAs single-crystal substrate is obtained.

[0071] The kinetic energy E of the photoelectrons emitted from the GaAs single-crystal substrate is calculated using the following mathematical formula, taking into account the energy hv (eV) of the applied X-rays and the binding energy E. B (eV) of the electrons in the GaAs single crystal substrate and the work function φ (eV) expressed. E=hv−EB−φ. From the kinetic energy distribution of the photoelectrons emitted by the GaAs single-crystal substrate, a spectrum is generated using the mathematical formula above, indicating the binding energy distribution of the photoelectrons. In the present embodiment, a Ga3d spectrum and an As3d spectrum, each indicating the binding energy distribution of the photoelectrons, are generated based on the kinetic energy distribution of the photoelectrons emitted from the position at depth d (nm) from the main surface of the GaAs single-crystal substrate. Here, in this description, the “Ga3d spectrum” refers to a spectrum representing the detection intensity of each photoelectron emitted from the 3d orbital of the Ga element (the Ga2O, the Ga2O3, and the Ga contained in the GaAs).The “As3d spectrum” refers to a spectrum that represents a detection intensity of each photoelectron emitted from the 3d orbital of the As element (As2O5, As2O3, metal As and the As contained in GaAs).

[0072] In XPS analysis, for precise measurement, each Ga3d and As3d spectra is obtained by performing a narrow scan within a predetermined binding energy range. Specifically, by performing a narrow scan within a binding energy range of 16 to 26 eV, the Ga3d spectrum can be plotted in a graph, with the horizontal axis representing the range and the vertical axis the detection intensities. Similarly, by performing a narrow scan within a binding energy range of 39 to 49 eV, the As3d spectrum can be plotted in a graph, with the horizontal axis representing the range and the vertical axis the detection intensities.

[0073] Narrow sampling is performed under conditions where the energy interval is 0.05 eV, the integration time at each energy value is 100 ms, and the number of integrations is one or more. Furthermore, the energy resolution E / ΔE is 3480.

[0074] In this way, a Ga3d spectrum LG, as in Fig. 3A shown, and an As3d spectrum LA, as in Fig. 3B shown, will be received. Fig. Figure 3A is a diagram showing an exemplary Ga3d spectrum after background correction, obtained on the basis of the XPS in which X-ray radiation is applied to the center of the main surface of the GaAs single crystal substrate according to the present embodiment. Fig. Figure 3B is a diagram showing an exemplary background-corrected As3d spectrum obtained based on the XPS where X-rays are applied to the center of the main surface of the GaAs single-crystal substrate according to the present embodiment. As described above, Fig. 3A and Fig. 3B shows the exemplary Ga3d spectrum and the As3d spectrum after background correction. This means that when determining the Ga3d spectrum LG and the As3d spectrum LA, the background correction is performed using the Shirley method (reference document: Kazuhiro Yoshihara: Journal of the Vacuum Society of Japan, 2013, Vol. 56, No. 6, pp. 243–247). Thus, the Ga3d spectrum LG after background correction can be determined based on the difference between the Ga3d spectrum obtained from the actual measurement and the background. Furthermore, the As3d spectrum LA after background correction can be determined based on the difference between the As3d spectrum obtained from the actual measurement and the background.

[0075] When determining the Ga3d spectrum LG, the peak of the detection intensities of the Ga element present as Ga2O (Ga) is used. + ) fixed at a position corresponding to a binding energy of 19.9 eV, and the peak position of the detection intensities of the Ga element present as Ga2O3 (Ga 3+ The peak of the detection intensities of the GaAs element (Ga-As) is fixed at a position corresponding to a binding energy of 20.7 eV. Furthermore, the peak of the detection intensities is fixed at a position corresponding to a binding energy of approximately 19.2 to 19.7 eV, giving it a width. This is because, when X-ray photoelectron spectroscopy is performed on the GaAs single crystal, a charge shift can occur, causing the Ga3d spectrum to be shifted by a maximum of approximately 1 eV towards the higher energy. Additionally, since the peak of the Ga-As detection intensities is influenced by the GaAs main layer, it is difficult to pinpoint the peak to a specific value, and the peak position is therefore set to a width of 0.5 eV, as described above.

[0076] When determining the As3d spectrum LA, the peak of the detection intensities of the As element present as As2O5 (As) is used. 5+ ) set to a position corresponding to a binding energy of 45.57 eV, and the peak position of the detection intensities of the As element present as As2O3 (As 3+ The peak of the detection intensities for the As element (metal-As), present as metal-As, is set to a position corresponding to a binding energy of approximately 41.62 to 42.12 eV, resulting in a broad spectrum. Similarly, the peak of the detection intensities for the As element (As-Ga), present as GaAs, is set to a position corresponding to a binding energy of approximately 40.77 to 41.27 eV, resulting in a broad spectrum of 77 to 41.27 eV. This is because, when X-ray photoelectron spectroscopy is performed on the GaAs single crystal, a charge shift can occur, causing the As3d spectrum to be shifted by a maximum of approximately 1 eV towards the higher energy.Furthermore, since each peak of the metal As and of the As-Ga is influenced by the main layer consisting of GaAs, it is difficult to define the peak to a specific value, and the peak position is therefore defined with a width of 0.5 eV as described above.

[0077] Next, the Ga3d spectrum LG, after background correction as described above, is expressed by separating the Ga3d spectrum LG into the following three Gaussian functions Y1, Y2, and Y3 (hereafter referred to as "peak separation"). In this way, the three spectra of the Ga element (Ga) can be determined. + ), which exists as Ga2O, of the Ga element (Ga 3+ ), which exists as Ga2O3, and of the Ga element (Ga-As), which exists as GaAs, are obtained by peak separation in the range of binding energy from 16 to 26 eV. Y1=a1*exp{(−(X−b1)2) / c12} Y2=a2*exp{(−(X−b2)2) / c22} Y3=a3*exp{(−(X−b3)2) / c32}

[0078] The unit of each of the Gaussian functions Y1, Y2 and Y3 is dimensionless, the unit of each of the X, b1, b2, b3, c1, c2 and c3 in the Gaussian functions Y1, Y2 and Y3 is eV, and the unit of each of the a1, a2 and a3 is dimensionless.

[0079] The Gaussian functions Y1 to Y3 are determined by optimizing each of the variables (a1, a2, a3, b1, b2, b3, c1, c2, c3) such that the square ([actual measurement - ΣGi] 2 ) a deviation from the actual measurement becomes minimal, provided that the i-th component of the Ga3d is given by the Gaussian function Gi = Ai*exp{(-(E-E1) 2 ) / Wi 2 } is expressed. Among these are the values ​​of the binding energy at the peaks of the detection intensities of the Ga. + , of the Ga 3+ and of the Ga-As, as described above, each replaced by b1 to b3.

[0080] That is, each of the variables (a1, a2, a3, b1, b2, b3, c1, c2, c3) is as follows. a1, a2, and a3 are each real numbers greater than or equal to 0. b1=19.9eV b2=20.7eV 19.2 eV ≤ b3 ≤ 19.7 eV 0.2eV≤c1≤0.95eV 0.2eV≤c2≤0.95eV 0.2eV≤c3≤0.95eV.

[0081] Thus, the Gaussian functions Y1, Y2 and Y3 can each be expressed as Ga + -Spectrum L2, Ga 3+ -Spectrum L1 and Ga-As spectrum L3 are represented, which are obtained, for example, by peak separation from the Ga3d spectrum LG in Fig. 3A will be received.

[0082] Furthermore, the As3d spectrum LA, after background correction as described above, can be expressed by peak separation in terms of the following four Gaussian functions Y4, Y5, Y6, and Y7. In this way, the four spectra of the As element present as As2O5 (As) can be determined. 5+ ), of the As element present as As2O3 (As 3+ ), of the As element present as metallic As (Metal-As) and of the As element present as GaAs (As-Ga), by peak separation in the range of binding energy from 39 to 49 eV. Y4=a4*exp{(−(X−b4)2) / c42} Y5=a5*exp{(−(X−b5)2) / c52} Y6=a6*exp{(−(X−b6)2) / c62} Y7=a7*exp{(−(X−b7)2) / c72}

[0083] The unit of each Gaussian function Y4, Y5, Y6 and Y7 is dimensionless, the unit of each X, b4, b5, b6, b7, c4, c5, c6 and c7 in the Gaussian functions Y4, Y5, Y6 and Y7 is eV, and the unit of each a4, a5, a6 and a7 is dimensionless.

[0084] The Gaussian functions Y4 to Y7 are determined by optimizing each of the variables (a4, a5, a6, a7, b4, b5, b6, b7, c4, c5, c6, c7) such that the square ([actual measurement - ΣGi] 2 ) a deviation from the actual measurement becomes minimal, provided that the i-th component of the As3d is given by the Gaussian function Gi = Ai*exp{(-(E-E1) 2 ) / Wi 2 } is expressed. The values ​​of the binding energy at the peaks of the signal intensities of the As 5+ , of the Ace 3+ The metals As and As-Ga, described above, are each placed in b4 to b7.

[0085] That is, each of the variables (a4, a5, a6, a7, b4, b5, b6, b7, c4, c5, c6, c7) is as follows. a4, a5, a6 and a7 are each real numbers greater than or equal to 0. b4=45.57eV b5=44.07eV 41.62eV≤b6≤42.12eV 40.77eV≤b7≤41.27eV 0.2eV≤c4≤0.95eV 0.2eV≤c5≤0.95eV 0.2eV≤c6≤0.95eV 0.2eV≤c7≤1.2eV.

[0086] Thus, the Gaussian functions Y4, Y5, Y6 and Y7 can each be considered as 5+ -Spectrum L4, As 3+ -Spectrum L5, metal-As spectrum L6 and As-Ga spectrum L7 are represented, which are obtained, for example, by peak separation from the As3d spectrum LA in Fig. 3B is obtained. Since the metal As is formed here due to a reaction of 2GaAs+As2O3→Ga2O3+4As from the oxide layer and the main layer, the metal As is detected by the XPS as intensity.

[0087] It should be noted that the following correction can be made to determine the peak positions of the Gaussian functions Y1 to Y7. First, the probability of photoelectron generation by X-rays, known as the photoionization efficiency (η), varies depending on the element, the X-ray energy, and similar factors. Therefore, the data published on the following website are used as the value for η. In particular, the photoionization efficiency (η) of X-rays with an incident energy of 600 eV is 0.28 for Ga3d and 0.42 for As3d.

[0088] https: / / vuo.elettra.eu / services / elements / WebElements.html (Please note that the data is based on the following documents: JJ Yeh, “Atomic Calculation of Photoionization Cross-Sections and Asymmetry Parameters”, Gordon and Breach Science Publishers, Langhorne, PE (USA), 1993, and JJ Yeh and I. Lindau, “Atomic Data and Nuclear Data Tables”, 32, 1-155 (1985)).

[0089] Since the intensity of the X-rays used in the synchrotron radiation facility decreases over time, an attenuation ratio of the Au4f photoelectron intensity is also determined by measuring a gold (Au) standard sample at regular intervals, and the dose of the X-rays used is corrected on the basis of this ratio.

[0090] In Fig. 3A corresponds to a range between the Ga 3+ -Spectrum L1 and the horizontal axis (X-axis) of the number of particles from the 3d orbital of Ga 3+ emitted photoelectrons and thus represents the integrated intensity of the Ga 3+ An area between the Ga + -Spectrum L2 and the horizontal axis (X-axis) corresponds to the number of particles from the 3d orbital of Ga + emitted photoelectrons and therefore represents the integrated intensity of the Ga + . A region between the Ga-As spectrum L3 and the horizontal axis (X-axis) corresponds to the number of photoelectrons emitted from the 3d orbital of the Ga-As and therefore represents the integrated intensity of the Ga-As.

[0091] In Fig. 3B corresponds to an area between the As 5+ -Spectrum L4 and the horizontal axis (X-axis) of the number of particles from the 3d orbital of As 5+ emitted photoelectrons and thus represents the integrated intensity of the As 5+ A region between the As 3+ -Spectrum L5 and the horizontal axis (X-axis) corresponds to the number of particles from the 3d orbital of As 3+ emitted photoelectrons and therefore represents the integrated intensity of the As 3+ A region between the metal-As spectrum L6 and the horizontal axis (X-axis) corresponds to the number of photoelectrons emitted from the 3d orbital of the metal-As and therefore represents the integrated intensity of the metal-As. A region between the As-Ga spectrum L7 and the horizontal axis (X-axis) corresponds to the number of photoelectrons emitted from the 3d orbital of the As-Ga and therefore represents the integrated intensity of the As-Ga.

[0092] Therefore, the ratio of the sum of the integrated intensity of As can be 5+ , the integrated intensity of As 3+ , the integrated intensity of As-Ga and the integrated intensity of metal-As to the sum of the integrated intensity of Ga + , the integrated intensity of Ga 3+ and the integrated intensity of Ga-As as the first integrated intensity ratio based on the areas obtained from the spectra above and the horizontal axis. Furthermore, the ratio of the sum of the integrated intensities of As can be determined. 5+ and the integrated intensity of As 3+ to the sum of the integrated intensity of Ga + and the integrated intensity of Ga 3+ as the fourth integrated intensity ratio based on the areas obtained from the spectra above and the horizontal axis.

[0093] According to the present embodiment, the second integrated intensity ratio and the fifth integrated intensity ratio can be determined in the same way as in the method described above for calculating the first integrated intensity ratio and the fourth integrated intensity ratio, except that the XPS is performed on the center of the main surface of the GaAs single crystal substrate under conditions of an incident energy of 600 eV and an exit angle of the photoelectrons of 45°.The third and sixth integrated intensity ratios can also be determined in the same way as in the procedure described above for calculating the first and fourth integrated intensity ratios, except that the XPS is performed on the center of the main surface of the GaAs single crystal substrate under conditions of an incident energy of 600 eV and an exit angle of the photoelectrons of 85°. <Gleichmäßigkeit der Hauptfläche des GaAs-Einkristallsubstrats>

[0094] The property of the GaAs single-crystal substrate according to the present embodiment is preferably uniform in the plane of the main surface. That is, the GaAs single-crystal substrate according to the present embodiment is preferably such that an epitaxial layer with a reduced turbidity value can be formed on it, regardless of its position in the plane of the main surface. The following embodiments (a first embodiment and a second embodiment) can be mentioned as examples of specific embodiments of such a preferred GaAs single-crystal substrate. (First embodiment)

[0095] The GaAs single-crystal substrate according to the first embodiment has a diameter of 75 mm or more and less than 150 mm. The GaAs single-crystal substrate preferably has a diameter of 75 mm or more and 105 mm or less. The GaAs single-crystal substrate has a seventh integrated intensity ratio, an eighth integrated intensity ratio, a ninth integrated intensity ratio, and a tenth integrated intensity ratio.The seventh and ninth integrated intensity ratios are each obtained by determining the spectra of the detection intensities of the 3d electrons of Ga and As with respect to the binding energy of a photoelectron emitted outwards from the GaAs single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed at each of the five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 30°.The eighth and tenth integrated intensity ratios are each obtained by determining the detection intensities of the 3d electrons of Ga and As with respect to the binding energy of a photoelectron emitted outwards from the GaAs single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed at each of the five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 85°.

[0096] The seventh and eighth integrated intensity ratios are each the ratio of the sum of the integrated intensities of the As element (As). 5+ ), which exists as As2O5, the integrated intensity of the As element present as As2O3 (As 3+ ), the integrated intensity of the As element present as GaAs (As-Ga) and the integrated intensity of the As element present as metallic As (Metal-As) to the sum of the integrated intensity of the Ga element present as Ga2O (Ga + ), the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ ) and the integrated intensity of the Ga element present as GaAs (Ga-As). The ninth and tenth integrated intensity ratios are each a ratio of the sum of the integrated intensity of the As element present as As₂O₅ (As₂O₅). 5+ ) and the integrated intensity of the As element present as As2O3 (As 3+ ), which, to a sum of the integrated intensity of the Ga element present as Ga2O (Ga + ) and the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ The standard deviation and mean of the eighth integrated intensity ratio satisfy a relationship of standard deviation / mean ≤ 0.01, and the standard deviation and mean of R1 / R2 satisfy a relationship of standard deviation / mean ≤ 0.07, where R1 / R2 is a ratio of ratio R1 and ratio R2, where ratio R1 is a ratio of the ninth integrated intensity ratio to the seventh integrated intensity ratio, and ratio R2 is a ratio of the tenth integrated intensity ratio to the eighth integrated intensity ratio. The lower bound of the standard deviation and mean of the eighth integrated intensity ratio is 0, which is an ideal value.For example, the standard deviation and mean of the eighth integrated intensity ratio can satisfy a standard deviation / mean relationship ≥ 0.008. The lower bound of the standard deviation and mean of R1 / R2 is 0, which is an ideal value, where R1 / R2 is the ratio of ratio R1 and ratio R2, where ratio R1 is the ratio of the ninth integrated intensity ratio to the seventh integrated intensity ratio, and ratio R2 is the ratio of the tenth integrated intensity ratio to the eighth integrated intensity ratio.For example, the standard deviation and mean value of R1 / R2 can satisfy a relationship of standard deviation / mean value ≥ 0.056, where R1 / R2 is the ratio of ratio R1 and ratio R2, where ratio R1 is the ratio of the ninth integrated intensity ratio to the seventh integrated intensity ratio and ratio R2 is the ratio of the tenth integrated intensity ratio to the eighth integrated intensity ratio.

[0097] If the standard deviation and mean value of the eighth integrated intensity ratio satisfy the relationship standard deviation / mean value ≤ 0.01, this means that a required amount of arsenic is present in the oxide layer. If the standard deviation and mean value of R1 / R2 satisfy the relationship standard deviation / mean value ≤ 0.07, this means that the arsenic in the oxide layer is distributed with the required uniformity without uneven distribution, where R1 / R2 is the ratio of ratio R1 and ratio R2, where ratio R1 is the ratio of the ninth integrated intensity ratio to the seventh integrated intensity ratio, and ratio R2 is the ratio of the tenth integrated intensity ratio to the eighth integrated intensity ratio.

[0098] If the diameter is represented by D, and two axes, each passing through the center of the main surface, lie on the main surface and are orthogonal to each other, are defined as the X-axis and Y-axis, then the coordinates (X, Y) of the five measurement points on the X-axis and Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), and (0, -D / 4). The units of D and each of the X- and Y-axes in the coordinates (X, Y) are mm. Thus, in the GaAs single-crystal substrate with a diameter of 75 mm or more and less than 150 mm, the main surface with the high mirror surface property can be obtained without deviations in the plane by effectively removing the oxide layer via thermal refining. Therefore, an epitaxial layer with a reduced turbidity value can be formed on the GaAs single-crystal substrate. (Second embodiment)

[0099] The GaAs single-crystal substrate according to the second embodiment has a diameter of 150 mm or more and 205 mm or less. The GaAs single-crystal substrate has an eleventh, a twelfth, a thirteenth, and a fourteenth integrated intensity ratio. The eleventh and thirteenth integrated intensity ratios are each obtained by determining the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outward from the GaAs single-crystal substrate. This determination is based on X-ray photoelectron spectroscopy, in which X-rays are directed at each of the nine measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 30°.The twelfth integrated intensity ratio and the fourteenth integrated intensity ratio are each obtained by determining the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the GaAs single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed at each of the nine measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and an exit angle of the photoelectrons of 85° at each of the nine measurement points on the main surface.

[0100] The eleventh and twelfth integrated intensity ratios are each a ratio of the sum of the integrated intensities of the As element present as As2O5 (As 5+ ), the integrated intensity of the As element present as As2O3 (As 3+ ), the integrated intensity of the As element present as GaAs (As-Ga) and the integrated intensity of the As element present as metallic As (Metal-As) to a sum of the integrated intensity of the Ga element present as Ga2O (Ga + ), the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ ) and the integrated intensity of the Ga element present as GaAs (Ga-As). The thirteenth integrated intensity ratio and the fourteenth integrated intensity ratio are each a ratio of the sum of the integrated intensity of the As element present as As₂O₅ (As₂O₅). 5+ ) and the integrated intensity of the As element present as As2O3 (As 3+ ) to a sum of the integrated intensity of the Ga element present as Ga2O (Ga + ) and the integrated intensity of the Ga element present as Ga2O3 (Ga 3+ A standard deviation and a mean value of the twelfth integrated intensity ratio satisfy a relationship of standard deviation / mean value ≤ 0.015, and a standard deviation and a mean value of R3 / R4 satisfy a relationship of standard deviation / mean value ≤ 0.078, where R3 / R4 is a ratio of a ratio R3 and a ratio R4, where ratio R3 is a ratio of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio, and ratio R4 is a ratio of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio. The lower bound of the standard deviation and the mean value of the twelfth integrated intensity ratio is 0, which is an ideal value.For example, the standard deviation and mean of the twelfth integrated intensity ratio can satisfy a standard deviation / mean relationship ≥ 0.010. The lower bound of the standard deviation and mean of R3 / R4 is 0, which is an ideal value, where R3 / R4 is the ratio of ratio R3 and ratio R4, where ratio R3 is the ratio of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio, and ratio R4 is the ratio of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio.For example, the standard deviation and mean value of R3 / R4 can satisfy a relationship of standard deviation / mean value ≥ 0.061, where R3 / R4 is the ratio of ratio R3 and ratio R4, where ratio R3 is the ratio of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio, and ratio R4 is the ratio of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio.

[0101] If the standard deviation and mean value of the twelfth integrated intensity ratio satisfy the relationship standard deviation / mean value ≤ 0.015, this means that a required amount of arsenic is present in the oxide layer. If the standard deviation and mean value of R3 / R4 satisfy the relationship standard deviation / mean value ≤ 0.078, this means that the arsenic is distributed with the required uniformity in the oxide layer without uneven distribution, where R3 / R4 is the ratio of ratio R3 to ratio R4, where ratio R3 is the ratio of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio, and ratio R4 is the ratio of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio.

[0102] If the diameter is represented by D and two axes, each passing through the center of the main surface, lie on the main surface and are orthogonal to each other, are defined as the X-axis and Y-axis, then the coordinates (X, Y) of the nine measurement points on the X-axis and Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), (0, -D / 4), (D / 2-10, 0), (0, D / 2-10), (-(D / 2-10), 0), and (0, -(D / 2-10)). The units of D and each of the X and Y coordinates (X, Y) are mm. Thus, in the GaAs single-crystal substrate with a diameter of 150 mm or more and 205 mm or less, the main surface with the high mirror surface property can be obtained without deviations in the plane by effectively removing the oxide layer by thermal refining. Therefore, an epitaxial layer with a reduced turbidity value can be formed on the GaAs single crystal substrate.

[0103] In each of the first and second implementations described above, a specific analytical procedure for determining each of the seventh integrated intensity ratios to the fourteenth integrated intensity ratios is identical to the procedure described in the section “Method for analyzing GaAs single crystal substrates by means of X-ray photoelectron spectroscopy (XPS) using synchrotron radiation”, which is why the same explanation is not repeated. (Five measuring points and nine measuring points)

[0104] The GaAs single-crystal substrate according to the first embodiment has a diameter of 75 mm or more and less than 150 mm. In this case, the five measurement points are positioned on the main surface of the GaAs single-crystal substrate according to the first embodiment as follows. That is, in order to evaluate the effect of the reduction in the turbidity value of the epitaxial layer due to the uniform distribution of each of the eight integrated intensity ratios and the R1 / R2 value in the plane, it is advantageous to position the five measurement points so that the distances between them are as large as possible and to measure the turbidity value that develops in the epitaxial layer that has grown in an area near each of the five measurement points. On this occasion, the turbidity value is preferably measured for an area with a diameter of 20 mm or more.Therefore, five circular measurement targets, each with a diameter of 20 mm, are positioned on the main surface of the GaAs single-crystal substrate, ensuring the greatest possible distance between them. The center point of each target is defined as the measurement point.

[0105] First, the two axes, each passing through the center of the main surface, are positioned on the main surface and defined orthogonally to each other as the X-axis and Y-axis. The coordinates (X, Y) of the first measurement point among the five measurement points on the X-axis and Y-axis are set to (0, 0). It should be noted that the X-axis and Y-axis are defined such that a notch formed in the GaAs single-crystal substrate lies in the third quadrant of the XY coordinate plane, and a general angle of a half-line passing through the notch forms 225° with a half-line extending from the origin in the positive direction of the X-axis.

[0106] Of the five measurement points, the second, third, fourth, and fifth are equally spaced along a perimeter consisting of a series of points each located D / 4 from the center of the GaAs single-crystal substrate. Specifically, the coordinates (X, Y) of the second measurement point are set to (D / 4, 0). The coordinates (X, Y) of the third measurement point are set to (0, D / 4). The coordinates (X, Y) of the fourth measurement point are set to (-D / 4, 0). The coordinates (X, Y) of the fifth measurement point are set to (0, -D / 4). D represents the diameter of the GaAs single-crystal substrate, and the units of D and each of the X and Y values ​​in the coordinates (X, Y) are mm.

[0107] The GaAs single-crystal substrate according to the second embodiment has a diameter of 150 mm or more and 205 mm or less. In this case, four additional measurement points are added to the main surface of the GaAs single-crystal substrate according to the second embodiment, in addition to the five measurement points defined in the GaAs single-crystal substrate according to the first embodiment. The total of nine measurement points are defined as follows: In addition to the second, third, fourth, and fifth measurement points described above, four measurement targets, each with a diameter of 20 mm, are defined on the main surface of the GaAs single-crystal substrate according to the second embodiment. These targets are located on the outer circumference relative to the measurement points and do not overlap with the measurement targets that overlap the second, third, fourth, and fifth measurement points.The center point of each of the measurement targets is defined as the measurement point, and X-rays are directed onto the measurement point. Specifically, the coordinates (X, Y) of the sixth measurement point of the four added measurement points are set to (0, D / 2-10). The coordinates (X, Y) of the seventh measurement point are set to (D / 2-10, 0). The coordinates (X, Y) of the eighth measurement point are set to (-(D / 2-10), 0). The coordinates (X, Y) of the ninth measurement point are set to (0, -(D / 2-10)). D represents the diameter of the GaAs single-crystal substrate, and the units of D and each of the X and Y values ​​in the coordinates (X, Y) are mm.

[0108] It is known that in a main surface with a large diameter of 150 mm or more and 205 mm or less, such as the main surface of the GaAs single-crystal substrate according to the second embodiment, a property tends to vary more in a region on the outermost circumferential side. Therefore, in order to evaluate the effect of the reduction in the turbidity value of the epitaxial layer due to the uniform distribution of the twelve integrated intensity ratios and the R3 / R4 value in the plane, it is desirable, in addition to the five measurement points described above, to measure the turbidity value that develops in the epitaxial layer in a region on the outermost circumferential side.To achieve this, in addition to the five measuring points described above on the main surface of the GaAs single crystal substrate, four measuring targets with a diameter of 20 mm each and measuring points that serve as the respective centers of the measuring targets are defined in the area on the outer circumferential side so that the distances between them are as large as possible.

[0109] Fig. Figure 4 is an explanatory diagram showing the five measurement points defined in the GaAs single crystal substrate with a diameter of 75 mm or more and less than 150 mm in the present embodiment. Fig. Figure 5 is an explanatory diagram showing the nine measurement points defined in the GaAs single crystal substrate with a diameter of 150 mm or more and 205 mm or less in the present embodiment.

[0110] As in Fig. As shown in Figure 4, in the GaAs single-crystal substrate according to the first embodiment, the X-axis and the Y-axis are each defined such that the general angle of the half-line passing through notch 50 is 225° with respect to the half-line extending from the origin in the positive direction of the X-axis. Next, a first measurement point P1 is defined at the origin (0, 0), the center of the GaAs single-crystal substrate, and a measurement target A1, a circular area with a diameter of 20 mm and the first measurement point P1 as its center, is defined.

[0111] Next, a second measurement point P2, a third measurement point P3, a fourth measurement point P4, and a fifth measurement point P5 are defined on a circumference consisting of a series of points, each located D / 4 from the center of the GaAs single-crystal substrate. Additionally, a measurement target A2, a measurement target A3, a measurement target A4, and a measurement target A5 are defined, each being a circular area with a diameter of 20 mm, centered on the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5, respectively.

[0112] If, for example, the in Fig. In the example shown in Figure 4, which represents a GaAs single-crystal substrate with a diameter of 75 mm, the coordinates (X, Y) (the units of X and Y are mm; the same applies to the description below) of the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 are set to (18.75, 0), (0, 18.75), (-18.75, 0), and (0, -18.75), respectively. Here, the measurement target A1 in the 75 mm diameter GaAs single-crystal substrate overlaps in some areas with the measurement targets A2, A3, A4, and A5. However, such overlap is acceptable because it is not detrimental from the perspective of evaluating the uniformity of the main surface of the GaAs single-crystal substrate.

[0113] As in Fig. Figure 5 shows that, in addition to the first measuring point P1 to the fifth measuring point P5, the GaAs single-crystal substrate according to the second embodiment includes a sixth measuring point P6, a seventh measuring point P7, an eighth measuring point P8 and a ninth measuring point P9, which are four measuring points that are fixed at equal intervals on the circumference located at the outer periphery with respect to the second measuring point P2, the third measuring point P3, the fourth measuring point P4 and the fifth measuring point P5, and offset inwards by 10 mm from the outer periphery of the GaAs single-crystal substrate.Furthermore, a measurement target A6, a measurement target A7, a measurement target A8 and a measurement target A9, which are circular areas with a diameter of 20 mm each and are centered on the sixth measurement point P6, the seventh measurement point P7, the eighth measurement point P8 and the ninth measurement point P9, are defined.

[0114] For example, if the example in Fig. As shown in Figure 5, a GaAs single-crystal substrate with a diameter of 150 mm is shown, the coordinates (X, Y) of the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5 are set to (37.5, 0), (0, 37.5), (-37.5, 0), and (0, 37.5), respectively. Furthermore, the coordinates (X, Y) of the sixth measurement point P6, the seventh measurement point P7, the eighth measurement point P8, and the ninth measurement point P9 are set to (65, 0), (0, 65), (-65, 0), and (0, -65), respectively. <epitaxieschicht>

[0115] The GaAs single-crystal substrate preferably has an epitaxial layer arranged on the main surface. In this case, the maximum haze value of any surface of the epitaxial layer is preferably 350 ppm or less, and the average haze value of the surface of the epitaxial layer is preferably 2.5 ppm or less. Alternatively, the maximum haze value of the surface of the epitaxial layer is preferably 100 ppm or less, and the average haze value of the surface of the epitaxial layer is preferably 2.0 ppm or less. The lower limit of both the maximum and average haze values ​​of the surface of the epitaxial layer is 0, which is an ideal value.

[0116] The epitaxial layer, for example, is a composite film made of Al 1-y-z Ga y In z As consists of, where y can be 0 or more and 1 or less, z can be 0 or more and 1 or less, and the sum of y and z can be 0 or more and 1 or less. That is, in the present embodiment, a composite layer of Al can be 1-y-z Ga y In z As (0≤y≤1, 0≤z≤1, 0≤y+z≤1) is applied as an epitaxial layer formed on the main surface of the GaAs single-crystal substrate. Furthermore, the epitaxial layer can be a composite layer of Al. x Ga 1-x N (0≤x≤1) or Al x Ga 1-x As (0≤x≤1).

[0117] The epitaxial layer is formed with a thickness of, for example, 0.5 to 10 µm. If the thickness of the epitaxial layer falls within the aforementioned range, the GaAs single-crystal substrate can be used in a wide range of applications. Preferably, the epitaxial layer has a thickness of 1 to 5 µm.

[0118] The turbidity value of the epitaxial layer located on the main surface of the GaAs single-crystal substrate can be determined using a conventional surface contaminant inspection instrument (for example, the "Surfscan 6420" from KLA-Tencor Corporation). The instrument can perform measurements across the entire surface of the epitaxial layer (except for a 2 mm inward margin from the substrate's outer perimeter) and determine the turbidity value (scattered light quantity (ppm)) per cm². 2 Measure on the surface of the epitaxial layer. Based on such a measurement result, the maximum and average values ​​of the surface turbidity of the epitaxial layer can be determined. [Method for the preparation of a gallium arsenide single crystal substrate]

[0119] A method for producing a gallium arsenide single-crystal substrate (GaAs single-crystal substrate) according to the present embodiment is preferably a method for producing the GaAs single-crystal substrate with the circular shape described above. The method comprises, for example: a step (preparation step) for preparing a gallium arsenide single-crystal substrate precursor (hereinafter also referred to as the "GaAs single-crystal substrate precursor") with a surface having a circular shape; and a purification step for obtaining the GaAs single-crystal substrate from the GaAs single-crystal substrate precursor. The purification step comprises: a step (surface polishing step) for forming the surface of the GaAs single-crystal substrate precursor into a polished surface by polishing the surface;a step (alkali cleaning step) to develop the polished surface into an alkali-cleaned surface by cleaning the polished surface with an alkali cleaning fluid; a step (first acid cleaning step) to develop the alkali-cleaned surface into an acid-cleaned surface by cleaning the alkali-cleaned surface by immersing the alkali-cleaned surface in a first acid cleaning fluid containing 0.3 ppm by mass or more and 0.5% by mass or less of a first acid;a step (second acid cleaning step) to form the acid-cleaned surface into a second acid-cleaned surface by cleaning the acid-cleaned surface by supplying a second acid cleaning fluid containing 0.3 wt. ppm or more and 0.5 wt. % or less of a second acid to the acid-cleaned surface at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more;and a step (heat treatment step) to form the second acid-cleaned surface into the main surface by performing a heat treatment on the second acid-cleaned surface in an inert gas atmosphere for 1 minute or longer and 30 minutes or less under atmospheric pressure and at temperatures of 150 °C or higher and 300 °C or lower. The first acid contained in the first acid cleaning fluid is at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid. The second acid contained in the second acid cleaning fluid is at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid.

[0120] The manufacturing process with this feature makes it possible to obtain a GaAs single-crystal substrate with a main surface bearing an oxide layer that can be effectively removed by thermal purification. The manufacturing process preferably includes a step (epitaxic layer formation step) for forming an epitaxial layer on the main surface. Thus, it is possible to obtain a GaAs single-crystal substrate with a main surface bearing an epitaxial layer with a reduced turbidity value.

[0121] In the present description, the term “gallium arsenide single crystal substrate precursor (GaAs single crystal substrate precursor)” refers to a GaAs single crystal substrate with a circular surface that has been cut from a gallium arsenide single crystal (hereinafter also referred to as “GaAs single crystal”) produced by a conventionally known manufacturing process such as a vertical boat process, and refers in particular to a GaAs single crystal substrate that is to be subjected to each step included in the purification step.

[0122] The inventors focused their attention on modifying a conventionally known purification step for obtaining the GaAs single-crystal substrate, based on insights gained from analysis using synchrotron radiation via the XPS described above. Specifically, it is known that the oxide layer of the GaAs single-crystal substrate is formed by surface oxidation during the acid purification step, in which impurities are removed in an alkaline cleaning agent that adheres to the surface of the GaAs single-crystal substrate precursor after the alkaline purification.Therefore, care was taken to carry out a process in which the oxide layer after the acid cleaning step has an As-rich composition, and a process in which metallic arsenic is generated near the interface between the oxide layer and the GaAs layer in the GaAs single-crystal substrate, and the oxide layer has an As₂O₃ rich composition due to a reduction action of the metallic arsenic. Specifically, after cleaning the surface of the GaAs single-crystal substrate precursor by performing the alkali cleaning step and the acid cleaning step in that order, the second acid cleaning step is carried out by a so-called spin cleaning, in which the acid cleaning fluid is applied to the surface while the surface is rotated, thereby further advancing the oxidation reaction of the GaAs to form the As-rich oxide layer on the surface.The surface was then subjected to heat treatment to promote the reducing effect of the metal arsenic near the interface, thereby modifying the oxide layer to have a composition rich in As₂O₃. Since such an oxide layer readily sublimates As₂O₃, it can be effectively removed by thermal purification. In this way, the inventors obtained a GaAs single-crystal substrate with a main surface exhibiting high mirror-like properties and thus arrived at a method for producing a GaAs single-crystal substrate on which an epitaxial film with a reduced turbidity value can be formed.

[0123] In the following, each of the steps included in the process for producing the GaAs single crystal substrate according to the present embodiment will be described with reference to Fig. 6 specifically described. Fig. Figure 6 is a flowchart showing the process for producing the GaAs single crystal substrate according to the present embodiment. <Vorbereitungsschritt S100>

[0124] The process for producing the GaAs single-crystal substrate includes the preparation step (S100) of preparing the GaAs single-crystal substrate precursor with a circular surface. In preparation step S100, the GaAs single-crystal substrate precursor required for the purification step is prepared. Preparation step S100 may include a step in which a conventionally known method for producing a GaAs single-crystal substrate precursor is carried out. That is, preparation step S100 may include a step for producing a GaAs single crystal using a conventionally known fabrication method, such as a vertical boat process, and for cutting out a GaAs single-crystal substrate precursor with a circular surface from the GaAs single crystal.It should be noted that when preparing a GaAs single-crystal substrate precursor with a (100) plane as the main face, for example, the GaAs single-crystal substrate precursor can be obtained by cutting it out of a GaAs single crystal that was in a <100> The growth direction is such that the (100) plane becomes the main surface. The preparation step S100 can also include a step to process the GaAs single-crystal substrate precursor cut from the GaAs single crystal to a desired size (for example, a disk shape with a diameter of 2 to 8 inches and a thickness of 250 to 1500 µm). A conventionally known method such as cutting or chamfering can be used as the processing method. <Reinigungsschritt S200>

[0125] The process for producing the GaAs single-crystal substrate includes a purification step S200, in which the GaAs single-crystal substrate is obtained from the GaAs single-crystal substrate precursor. This purification step S200 allows the GaAs single-crystal substrate to be obtained from the GaAs single-crystal substrate precursor with the main surface containing the oxide film, which can be effectively removed by thermal purification. Purification step S200 comprises: a step (surface polishing step S210) to form the surface of the GaAs single-crystal substrate precursor with a polished surface by polishing the surface; and a step (alkali cleaning step S220) to form the polished surface with an alkaline cleaning solution.a step (first acid cleaning step S230) to form the alkali-cleaned surface into an acid-cleaned surface by cleaning the alkali-cleaned surface by immersing the alkali-cleaned surface in a first acid cleaning fluid containing 0.3 ppm by mass or more and 0.5% by mass or less of a first acid; a step (second acid cleaning step S240) to form the acid-cleaned surface into a second acid-cleaned surface by cleaning the acid-cleaned surface by supplying a second acid cleaning fluid containing 0.3 ppm by mass or more and 0.5% by mass or less of a second acid to the acid-cleaned surface at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more;and a step (heat treatment step S250) to form the surface cleaned with the second acid into the main surface by performing a heat treatment on the surface cleaned with the second acid in an inert gas atmosphere for 1 minute or longer and 30 minutes or less under atmospheric pressure and a temperature of 150 °C or more and 300 °C or less. The individual steps of cleaning step S200 are described in detail below. (Surface polishing step S210)

[0126] Surface polishing step S210 is the step in which the surface of the GaAs single-crystal substrate precursor is polished. This step results in a mirror-smooth, polished surface. For example, surface polishing step S210 can achieve a surface roughness of 0.3 nm or less, expressed as the arithmetic mean roughness Ra. Various polishing methods can be used in surface polishing step S210, including conventional mechanical and chemical-mechanical polishing techniques. (Alkali cleaning step S220)

[0127] Alkaline cleaning step S220 is the step in which the polished surface is transformed into an alkaline-cleaned surface by cleaning it with the alkaline cleaning fluid. Alkaline cleaning step S220 removes foreign matter, impurities, or the like that adhering to the polished surface of the GaAs single-crystal substrate precursor using the alkaline cleaning fluid. The alkaline cleaning fluid is not particularly restricted, but preferably an aqueous solution containing 0.1 to 10 wt% of an organic alkali compound that does not contain any metallic element that affects the electrical properties is used. Examples of the organic alkali compound include a quaternary ammonium hydroxide such as choline or tetramethylammonium hydroxide (TMAH), a quaternary pyridinium hydroxide, or the like. (First acid cleaning step S230)

[0128] The first acid cleaning step, S230, is the step in which the alkali-cleaned surface is converted to an acid-cleaned surface by immersing the alkali-cleaned surface in the acid cleaning fluid containing 0.3 ppm or more by mass and 0.5% or less by mass of the first acid. The first acid cleaning step, S230, removes impurities present in the alkali cleaning fluid and adhering to the alkali-cleaned surface of the GaAs single-crystal substrate precursor through an oxidation reaction (etching of the alkali-cleaned surface) with the first acid cleaning fluid. Specifically, in the first acid cleaning step, S230, the alkali-cleaned surface is immersed in the first acid cleaning fluid, which contains 0.3 ppm or more by mass and 0.5% or less by mass of the first acid.This ensures that the ratio of Ga atoms to As atoms in the main surface is appropriate, allowing the oxide layer to be efficiently removed by thermal cleaning. In the first acid cleaning step S230, the alkali-cleaned surface is preferably cleaned with a first acid cleaning fluid containing 0.3 ppm by mass or more and 0.3 percent by mass or less of the first acid.

[0129] If the concentration of the first acid in the first acid cleaning solution is less than 0.3 ppm by mass, the modifying effect on the alkali-cleaned surface will be minimal. Conversely, the influence of carbon dioxide (CO2) gas dissolved in the first acid cleaning solution from the ambient air will be significant, thus altering the chemical composition of the acid-cleaned surface after the first acid cleaning step (S230). If the concentration of the first acid in the first acid cleaning solution is greater than 0.5% by mass, the chemical composition of the acid-cleaned surface (and the main surface in the subsequent step) will tend to change, as the deviation of the acid-cleaned surface from stoichiometry due to the effect of the first acid is substantial.The term "stoichiometry" here means that, given the presence of a particular compound, the ratio (the composition) of the atoms that make up the compound corresponds to the chemical formula value.

[0130] The acid contained in the acid cleaning fluid is not particularly restricted, but preferably an acid component with high cleaning power, which does not contain any element (for example, a metal element, sulfur, or the like) that impairs the electrical properties, and which is less likely to cause serious secondary contamination and system deterioration when the acid component evaporates together with a water component and droplets are distributed throughout the system. For example, the acid in the acid cleaning fluid preferably contains at least one inorganic acid selected from the group consisting of hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3), and nitrous acid (HNO2). An organic acid such as acetic acid, citric acid, or malic acid may also preferably be used.Furthermore, two or more of these acids can be used in combination; for example, hydrochloric acid and nitric acid can be used in combination.

[0131] From a cleaning properties perspective, the first acid cleaning solution preferably contains 0.3 ppm to 0.3% hydrogen peroxide (H₂O₂) by mass. If the H₂O₂ concentration is less than 0.3 ppm by mass, the influence of dissolved oxygen in the first acid cleaning solution can be significant, reducing its effectiveness in promoting contaminant removal. If the H₂O₂ concentration is greater than 0.3% by mass, the etching rate can become too high, potentially leading to uneven etching of the acid-cleaned surface.

[0132] After the first acid cleaning step S230, preferably immediately after the first acid cleaning step S230, the acid-cleaned surface of the GaAs single-crystal substrate precursor is preferably cleaned with pure water. The cleaning process with pure water is not particularly restricted, but the acid-cleaned surface of the GaAs single-crystal substrate precursor is preferably cleaned for 5 minutes or less with pure water having a dissolved oxygen concentration (DO) of 100 ppb or less. In this way, the progression of excessive oxidation of the acid-cleaned surface can be suppressed. Here, the dissolved oxygen concentration of the pure water is preferably 50 ppb or less from the perspective of further suppressing the progression of excessive oxidation. The total organic carbon (TOC) content of the pure water is preferably 40 ppb or less to ensure low contamination.The purification process with pure water can also be carried out by applying the pure water to the acid-cleaned surface while the GaAs single-crystal substrate precursor is rotated circumferentially at a speed of 100 to 800 rpm, keeping its main surface horizontal. (Second acid cleaning step S240)

[0133] The second acid cleaning step, S240, is the step in which the acid-cleaned surface is formed into the second acid-cleaned surface by cleaning it with the second acid cleaning fluid at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more. The second acid cleaning step, S240, further promotes the oxidation reaction of the GaAs in the acid-cleaned surface, thereby enabling the acid-cleaned surface to acquire an As-rich composition.Thus, in the heat treatment step S250 described below, the reduction effect of the metal arsenic near the interface between the oxide layer and the main layer can be efficiently promoted, with the result that the oxide layer can be modified to have a composition rich in As2O3.

[0134] In particular, the second acid contained in the second acid cleaning fluid is at least one acid selected from the group consisting of hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3), and nitrous acid (HNO2). Each of these acids is advantageous because it is an acid component with high cleaning power, contains no element (e.g., a metallic element, sulfur, or the like) that impairs the electrical properties, and is less likely to cause serious secondary contamination and deterioration of the equipment when the acid component evaporates together with a water component and droplets are distributed throughout the system. The second acid cleaning fluid preferably contains an organic acid such as acetic acid, citric acid, or malic acid. Furthermore, two or more of these acids can be used in combination; for example, hydrochloric acid and nitric acid can be used together.The concentration of the second acid in the second acid cleaning solution is preferably 0.3 ppm by mass or more and 0.5% by mass or less. If the concentration of the second acid in the second acid cleaning solution is less than 0.3 ppm by mass, its effect on promoting the progression of oxidation on the acid-cleaned surface will be minimal. Conversely, if the concentration of the second acid in the second acid cleaning solution is more than 0.5% by mass, the chemical composition of the acid-cleaned surface (and the main surface in the subsequent step) tends to vary because the deviation of the acid-cleaned surface from stoichiometry is large. The concentration of the second acid in the second acid cleaning solution is preferably 0.3 ppm by mass or more and 0.3% by mass or less.

[0135] It should be noted that in the first acid cleaning step S230, described above as an example, the first acid contained in the first acid cleaning fluid is at least one acid selected from the group consisting of hydrofluoric acid (HF), hydrochloric acid (HCl), nitric acid (HNO3), and nitrous acid (HNO2). The first acid and the second acid each contain at least one acid from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid, and the second acid may be of the same type as the first acid. Each of the first acid and the second acid contains at least one acid selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid, and nitrous acid, and the second acid may be a different type of acid than the first acid.That is, both the first acid and the second acid contain at least one acid from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid and nitrous acid, and the second acid may be of the same type as the first acid or a different type of acid than the first acid.

[0136] In the second acid cleaning step S240, the acid-cleaned surface is preferably rotated circumferentially at a speed of 1500 rpm or more. The upper limit of the rotational speed for rotating the acid-cleaned surface circumferentially is not particularly limited, but is preferably 2500 rpm. The flow rate of the second acid cleaning fluid supplied to the acid-cleaned surface is preferably 0.1 l / min or more and 1 l / min or less. The time for supplying the second acid cleaning fluid to the acid-cleaned surface is preferably 30 seconds or more and 1 minute or less. This allows for better control of the oxidation reaction of the GaAs in the acid-cleaned surface.

[0137] Furthermore, after the second acid cleaning step S240, preferably immediately after the second acid cleaning step S240, the second acid-cleaned surface of the GaAs single-crystal substrate precursor is preferably cleaned with pure water. The cleaning process with pure water is not particularly restricted, but the second acid-cleaned surface of the GaAs single-crystal substrate precursor is preferably cleaned for 5 minutes or less with pure water having a dissolved oxygen concentration (DO) of 100 ppb or less. In this way, impurities adhering to the second acid-cleaned surface can be removed. Here, the dissolved oxygen concentration of the pure water is preferably 50 ppb or less to further suppress the progression of excessive oxidation.The total organic carbon (TOC) content of the pure water is preferably 40 ppb or less to ensure low contamination. The purification process using pure water can also be carried out by feeding the pure water to the second acid-cleaned surface while the GaAs single-crystal substrate precursor is rotated at a speed of 100 rpm or more, with its main face held horizontally. (Heat treatment step S250)

[0138] Heat treatment step S250 is the step in which the second acid-cleaned surface is transformed into the primary surface by subjecting it to heat treatment in an inert gas atmosphere at atmospheric pressure and temperatures of 150 °C or higher and 300 °C or lower for 1 minute or more and 30 minutes or less. Heat treatment step S250 enhances the reducing effect of the metal arsenic on the oxide layer of the second acid-cleaned surface, modifying the oxide layer to have a composition rich in As₂O₃. This allows the As₂O₃ to readily sublime, thus enabling effective removal of the oxide layer by thermal cleaning.

[0139] In heat treatment step S250, the heat treatment of the second acid-cleaned surface is carried out in an inert gas atmosphere for 1 minute or longer and 30 minutes or less under atmospheric pressure and temperatures of 150 °C or more and 300 °C or less. The type of inert gas is not particularly restricted, but argon or nitrogen are preferred. The temperature at which the heat treatment is carried out is preferably 150 to 200 °C. The duration of the heat treatment is preferably 1 to 5 minutes. By carrying out the heat treatment under the conditions in the aforementioned ranges, the composition of the oxide layer can be appropriately controlled. If the temperature of the heat treatment is below 150 °C or the duration of the heat treatment is less than 1 minute, the oxide layer tends to be insufficiently modified.If the temperature of the heat treatment exceeds 300 °C or the duration of the heat treatment is more than 30 minutes, the GaAs single crystal substrate may be affected by excessive heating. <Filmbildungs-Schritt S300> (Thermal cleaning step S310)

[0140] In the manner described above, the method for producing the GaAs single-crystal substrate according to the present embodiment makes it possible to obtain the GaAs single-crystal substrate with the major surface area containing the oxide film with the composition rich in As and rich in As₂O₃. The GaAs single-crystal substrate is preferably subjected to a thermal purification step S310 and an epitaxial film formation step S320, which are described below as film formation step S300. Even if the thermal purification of the GaAs single-crystal substrate is carried out under conventionally known conditions (for example, under a heat treatment at 550 °C for a duration of 5 minutes) in thermal purification step S310, Ga₂O and As₂O₃ are readily sublimed, so that the oxide layer can be effectively removed. <Schritt S320 zur Bildung der Epitaxieschicht>

[0141] Furthermore, the method for producing the GaAs single-crystal substrate according to the present embodiment preferably comprises the step (step S320 for forming the epitaxial layer) of forming an epitaxial film on the main surface, as described above. Step S320 for forming the epitaxial film allows the GaAs single-crystal substrate to be obtained with a main surface on which an epitaxial film with a reduced turbidity value is formed. For example, a maximum turbidity value of a surface of the epitaxial film can be 350 ppm or less, and an average turbidity value of the surface can be 2.5 ppm or less, thereby achieving improved device performance.

[0142] A conventionally known method can be used to form the epitaxial film on the main surface of the GaAs single-crystal substrate in step S320. The property of the epitaxial film obtained in this step is the same as described above in the section "Epitaxial Film," and therefore the same explanation is not repeated. Since the GaAs single-crystal substrate, which forms the main surface on which the epitaxial film is formed, has a sufficiently low turbidity value, the GaAs single-crystal substrate can be used for devices such as field-effect transistors, microwave diodes, other integrated circuits, and the like. Examples

[0143] The present disclosure is further described below by means of examples, but is not limited to such examples. GaAs single-crystal substrates of samples 1 to 6 described below are examples of the present disclosure, and GaAs single-crystal substrates of samples 11 to 13 are comparative examples. [Production of GaAs single crystal substrates]<Probe 1> (Preparatory step)

[0144] Several GaAs single-crystal substrate precursors, each with a diameter of 6 inches (150 mm) and a thickness of 675 µm, were prepared by cutting and chamfering a semi-insulating GaAs single crystal to which carbon atoms (C) had been added and which had been grown using the Vertical Bridgman (VB) method. (Surface polishing step)

[0145] One surface of each GaAs single-crystal substrate precursor was subjected to conventional mechanical polishing and chemical-mechanical polishing. This resulted in the production of a GaAs single-crystal substrate precursor with a polished surface exhibiting an arithmetic mean roughness Ra of 0.3 nm or less according to JIS B0601:2001 and an off-angle of 2° to the (100) plane. (Alkaline cleaning step)

[0146] The polished surface of the GaAs single-crystal substrate precursor was immersed for 10 minutes at room temperature (25 °C) in an aqueous solution (alkaline cleaning fluid) containing 0.5 wt% tetramethylammonium hydroxide using a vertical batch process. The GaAs single-crystal substrate precursor was then rinsed for 3 minutes with ultrapure water (electrical resistance (resistivity) of 18 MΩ·cm or more, TOC (total organic carbon) of less than 10 µg / L, and the number of fine particles of less than 100 particles / L; the same applies to the description below). (First acid cleaning step)

[0147] The alkali-cleaned surface of the GaAs single-crystal substrate precursor was immersed in an aqueous hydrochloric acid solution (first acid cleaning solution) containing 0.3 wt ppm hydrochloric acid for 2 minutes at room temperature (25 °C) according to the vertical batch procedure. The GaAs single-crystal substrate precursor was then rinsed for 3 minutes with the same ultrapure water used in the alkali cleaning step. This process converted the alkali-cleaned surface to an acid-cleaned surface. (Second acid cleaning step)

[0148] The acid-cleaned surface of the GaAs single-crystal substrate precursor was subjected to acid cleaning using a spin cleaning process and a second acid cleaning solution. Specifically, an aqueous hydrochloric acid solution (second acid cleaning solution) containing 0.3 ppm hydrochloric acid by mass was applied to the acid-cleaned surface of the GaAs single-crystal substrate precursor, which was rotated circumferentially at 1500 rpm, at a flow rate of 0.1 L / min for 1 minute. The GaAs single-crystal substrate precursor was then rinsed for 3 minutes with the same ultrapure water used in the first acid cleaning step. This process transformed the acid-cleaned surface into the second acid-cleaned surface. (Heat treatment step)

[0149] The second acid-cleaned surface of the GaAs single-crystal substrate precursor was subjected to heat treatment under an argon gas atmosphere at atmospheric pressure and 200°C for 1 minute. This transformed the second acid-cleaned surface into a primary surface with a predetermined oxide film. In this way, the required number of GaAs single-crystal substrates of sample 1 were obtained. The diameter and thickness of the GaAs single-crystal substrate precursor were maintained in each of the GaAs single-crystal substrates. (Step in the formation of the epitaxial film)

[0150] The GaAs single-crystal substrate underwent thermal cleaning for 5 minutes at 550 °C. Subsequently, a 5 µm thick Al layer was applied. 0,5 Ga 0,5 An arsenic layer was deposited as an epitaxial layer onto the main surface of one of the thermally purified GaAs single-crystal substrates using metal-organic vapor phase epitaxy (MOVPE). The GaAs single-crystal substrate on whose main surface the epitaxial layer was grown is hereinafter referred to as the "epitaxial substrate." In this way, the epitaxial substrate of sample 1 was obtained. During the growth of the epitaxial layer, the GaAs single-crystal substrate was heated to 550 °C. <Probe 2>

[0151] A required number of GaAs single-crystal substrates of sample 2 were obtained in the same manner as in sample 1, except that the acid purification according to the spin purification procedure was carried out under the following conditions in the second acid purification step, and the heat treatment was carried out under the following conditions. Additionally, an Al 0,5 Ga 0,5 An arsenic layer 5 µm thick was grown as an epitaxial layer on the main surface of one of the GaAs single-crystal substrates in the same manner as in Sample 1. The acid cleaning conditions following the spin-cleaning procedure for Sample 2 were such that an aqueous hydrochloric acid solution (second acid cleaning solution) containing 0.3 ppm hydrochloric acid by mass was applied at a flow rate of 1 l / min for 30 seconds to the acid-cleaned surface of the GaAs single-crystal substrate precursor, which was being rotated circumferentially at 2500 rpm. The heat treatment conditions for Sample 2 were such that the heat treatment was carried out under an argon gas atmosphere at atmospheric pressure and 150 °C for 5 minutes. <Probe 3>

[0152] A required number of GaAs single-crystal substrates of sample 3 were obtained in the same manner as in sample 1, except that the acid purification according to the spin purification procedure was carried out under the following conditions in the second acid purification step, and the heat treatment was carried out under the following conditions. Subsequently, an Al was deposited on the main surface of one of the GaAs single-crystal substrates in the same manner as in sample 1. 0,5 Ga 0,5 An As layer with a thickness of 5 µm was grown as an epitaxial layer. The conditions for acid cleaning following the spin cleaning process for the production of sample 3 are such that an aqueous hydrochloric acid solution (second acid cleaning solution) containing 0.3 wt ppm hydrochloric acid is applied to the acid-cleaned surface of the GaAs single-crystal substrate precursor, which is rotated circumferentially at 1500 rpm, at a flow rate of 5 l / min for 5 minutes. The conditions for the heat treatment step for the production of sample 3 are such that the heat treatment is carried out under an argon gas atmosphere at atmospheric pressure and 200 °C for 1 minute. <Probe 4>

[0153] A required number of GaAs single-crystal substrates of sample 4 were obtained in the same manner as in sample 1, except that the acid purification according to the spin purification procedure was carried out under the following conditions in the second acid purification step, and the heat treatment was carried out under the following conditions. Subsequently, an Al was deposited on the main surface of one of the GaAs single-crystal substrates in the same manner as in sample 1. 0,5 Ga 0,5 An As layer with a thickness of 5 µm was grown as an epitaxial layer. The conditions for acid cleaning following the spin-cleaning process for the preparation of sample 4 are such that an aqueous hydrochloric acid solution (second acid cleaning solution) with 0.3 wt ppm hydrochloric acid is applied to the acid-cleaned surface of the GaAs single-crystal substrate precursor, which is rotated circumferentially at 1500 rpm, at a flow rate of 0.1 l / min for 5 minutes. The conditions for the heat treatment step for the preparation of sample 4 are such that the heat treatment is carried out under an argon gas atmosphere at atmospheric pressure and 300 °C for 1 minute. <Probe 5>

[0154] A required number of GaAs single-crystal substrates of sample 5 were obtained in the same manner as in sample 1, except that the acid purification according to the spin purification procedure was carried out under the following conditions in the second acid purification step, and the heat treatment was carried out under the following conditions. Subsequently, an Al was deposited on the main surface of one of the GaAs single-crystal substrates in the same manner as in sample 1. 0,5 Ga 0,5 An As layer with a thickness of 5 µm was grown as an epitaxial layer. The conditions for acid cleaning following the spin cleaning process for the production of sample 5 are such that an aqueous hydrochloric acid solution (second acid cleaning solution) with 0.3 wt ppm hydrochloric acid is applied to the acid-cleaned surface of the GaAs single-crystal substrate precursor, which is rotated circumferentially at 1500 rpm, at a flow rate of 0.1 l / min for 1 minute. The conditions for the heat treatment step for the production of sample 5 are such that the heat treatment is carried out under an argon gas atmosphere at atmospheric pressure and 150 °C for 30 minutes. <Probe 6>

[0155] A required number of GaAs single-crystal substrates of sample 6 were obtained in the same manner as in sample 1, except that the acid purification according to the spin purification procedure was carried out in the second acid purification step under the following conditions, and the heat treatment was carried out under the following conditions. Subsequently, an Al was deposited on the main surface of one of the GaAs single-crystal substrates in the same manner as in sample 1. 0,5 Ga 0,5 An As layer with a thickness of 5 µm was grown as an epitaxial layer. The conditions for acid cleaning following the spin cleaning process for the preparation of sample 6 are such that an aqueous hydrochloric acid solution (second acid cleaning solution) with 0.3 wt ppm hydrochloric acid is applied to the acid-cleaned surface of the GaAs single-crystal substrate precursor, which is rotated circumferentially at 1500 rpm, at a flow rate of 0.1 l / min for 5 minutes. The conditions for the heat treatment step for the preparation of sample 6 are such that the heat treatment is carried out under an argon gas atmosphere at atmospheric pressure and 300 °C for 30 minutes. <Probe 11>

[0156] The required number of GaAs single-crystal substrates of sample 11 were obtained in the same manner as in sample 1, except that the heat treatment step was omitted. Furthermore, an Al 0,5 Ga 0,5 An As layer with a thickness of 5 µm was grown as an epitaxial layer on the main surface of one of the GaAs single crystal substrates in the same way as in sample 1. <Probe 12>

[0157] The required number of GaAs single-crystal substrates of sample 12 were obtained in the same manner as in sample 1, except that the second acid purification step was omitted. Furthermore, an Al 0,5 Ga 0,5 An As layer with a thickness of 5 µm was grown as an epitaxial layer on the main surface of one of the GaAs single crystal substrates in the same way as in sample 1. <Probe 13>

[0158] The required number of GaAs single-crystal substrates of sample 13 were obtained in the same manner as in sample 1, except that the second acid purification step and the heat treatment step were omitted. Furthermore, an Al 0,5 Ga 0,5 An As layer with a thickness of 5 µm was grown as an epitaxial layer on the main surface of one of the GaAs single crystal substrates in the same way as in sample 1. [First test]<Analyse von GaAs-Einkristallsubstraten mittels Röntgen-Photoelektronenspektroskopie>

[0159] X-rays with an energy of 600 eV were generated using "BL17," one of the beamlines exclusively available to Sumitomo Electric Industries at the SAGA Light Source. The X-rays were directed onto the center of the main surface of each of the GaAs single-crystal substrates of samples 1 to 6 and samples 11 to 13, enabling analysis by X-ray photoelectron spectroscopy. Since the GaAs single-crystal substrates of samples 1 to 6 and samples 11 to 13 could not be fully placed on a sample stage, a test piece was cut from each of the GaAs single-crystal substrates of samples 1 to 6 and samples 11 to 13, and the analysis was performed on this test piece.

[0160] The analysis conditions are as follows. Condition 1: X-ray incidence energy of 600 eV and photoelectron exit angle of 30° Condition 2: X-ray incidence energy of 600 eV and photoelectron exit angle of 45° Condition 3: X-ray incidence energy of 600 eV and photoelectron exit angle of 85° Size of the test piece under each condition: 10 mm × 10 mm Pressure around the test piece under all conditions: 4×10 -7 Pa High-resolution XPS analyzer (trade name: "R3000" from Scienta Omicron) used under all conditions Energy resolution E / ΔE: 3480 Plot interval for coupling energy: 0.02 eV Integration time and number of integrations for each energy value: 100 ms and 50 times.

[0161] Based on a Ga3d spectrum and an As3d spectrum obtained by XPS analysis under each of the above conditions (conditions 1 to 3), a first integrated intensity ratio (In1), a second integrated intensity ratio (In2), and a third integrated intensity ratio (In3) were obtained, where each ratio is a sum of an integrated intensity of As 5+ , an integrated intensity of As 3+ , an integrated intensity of As-Ga and an integrated intensity of metal-As to a sum of an integrated intensity of Ga + , an integrated intensity of Ga 3+ and an integrated intensity of Ga-As in each of samples 1 to 6 and samples 11 to 13. Based on the Ga3d spectrum and the As3d spectrum obtained by analysis under each of the above conditions (conditions 1 to 3), a fourth integrated intensity ratio (In4), a fifth integrated intensity ratio (In5), and a sixth integrated intensity ratio (In6) were obtained, each representing a ratio of the sum of the integrated intensities of the As. 5+ and an integrated intensity of the acetylcholine 3+ to a sum of an integrated intensity of the Ga + and an integrated intensity of the Ga 3+ in each of samples 1 to 6 and samples 11 to 13. A ratio (In1 / In3) of the first integrated intensity ratio (In1) to the third integrated intensity ratio (In3) in each of samples 1 to 6 and samples 11 to 13 was also calculated. Furthermore, a ratio (In4 / In1) of the fourth integrated intensity ratio (In4) to the first integrated intensity ratio (In1), a ratio (In5 / In2) of the fifth integrated intensity ratio (In5) to the second integrated intensity ratio (In2), and a ratio (In6 / In3) of the sixth integrated intensity ratio (In6) to the third integrated intensity ratio (In3) in each of samples 1 to 6 and samples 11 to 13 were calculated. The results are presented in Tables 1 and 2. In Tables 1 and 2, "Total Ga" denotes the sum of the integrated intensities of Ga. + , the integrated intensity of Ga 3+ and the integrated intensity of Ga-As, and "Total-As" denotes the sum of the integrated intensity of As 5+ , the integrated intensity of As 3+ , the integrated intensity of As-Ga and the integrated intensity of metal As. <Maximalwert und Durchschnittswert der Trübung der Oberfläche des Epitaxiefilms>

[0162] For the surface of the epitaxial film in each of the epitaxial substrates of samples 1 to 6 and samples 11 to 13, a maximum and an average surface turbidity value of the epitaxial film were determined in each sample using a surface contaminant inspection device (trade name: "Surfscan 6420" by KLA-Tencor Corporation). The results are presented in Tables 1 and 2.

[0163] Furthermore, based on the maximum and average values ​​of the surface turbidity of the epitaxial film, the quality of the epitaxial substrate of each of samples 1 to 6 and samples 11 to 13 was determined according to the following criteria. The results are presented in Tables 1 and 2. A: The maximum turbidity value is 100 ppm or less and the average turbidity value is 2.0 ppm or less; B: The maximum turbidity value is more than 100 ppm and 350 ppm or less, and the average turbidity value is 2.5 ppm or less; and C: At least the maximum turbidity value is more than 350 ppm or the average turbidity value is more than 2.5 ppm. [Table 1] Table 1 ProbeNo. 600eV In1 Price (ppm) Review 30° 45° 85° / In3 Max Durchschnitt 1 Gesamt As / Gesamt GaAs-O / Ga-O(As-O / Ga-O) / (Gesamt As / GesamtGa)Gesamt As / Gesamt Ga 1.11(In1)0.97(In4)0.87(In4 / In1)1.10(In1) 1.09(In2)0.91(In5)0.83(In5 / In2)1.11(In2) 1.09(In3)1.02(In6)0.94(In6 / In3)1.07(In3) 1,021,03 11 1,03 A 2 As-O / Ga-O(As-O / Ga-O) / (Gesamt As / GesamtGa)Gesamt As / Gesamt Ga 1.10(In4)1.00(In4 / In1)1.22(In1) 1.15(In5)1.04(In5 / In2)1.17(In2) 1.09(In6)1.02(In6 / In3)1.14(In3) 1,07 16 1,18 A 3 As-O / Ga-O(As-O / Ga-O) / (Gesamt As / GesamtGa)Gesamt As / Gesamt Ga 1.12(In4)0.92(In4 / In1)1.21(In1) 1.02(In5)0.87(In5 / In2)1.19(In2) 1.09 (In6)0.96(In6 / In3)1.05 (In3) 1,15 251 2,10 B 4 As-O / Ga-O(As-O / Ga-O) / (Gesamt As / GesamtGa)Gesamt As / Gesamt Ga 1.17(In4)0.97(In4 / In1)1.35(In1) 1.23(In5)1.03(In5 / In2)1.15(In2) 1.07 (In6)1.02(In6 / In3)1.08 (In3) 1,25 341 2,30 B 5 As-O / Ga-O(As-O / Ga-O) / (Gesamt As / GesamtGa) 1.06(In4)0.79(In4 / In1) 1.09(In5)0.95(In5 / In2) 1.13(In6)1.05(In6 / In3) 157 1,50 B 6 Total As / Total GaAs-O / Ga-O 1.21 (In1)0.90 (In4) 1.17 (In2) 1.05 (In5) 1.06 (In3) 1.13 (In6) 1,14 184 1,20 B (As-O / Ga-O) / (Total As / Total Ga) 0.74(In4 / In1) 0.89(In5 / In2) 1.07(In6 / In3) [Table 2] Table 2 Sample No. 600eV In1 / In3 Turbidity (ppm) Evaluation 30° 45° 85° Max Average 11 Total As / Total GaAs-O / Ga-O(As-O / Ga-O) / (Total As / Total Ga) 0.99 (In1)0.90 (In4)0.91(In4 / In1) 0.99 (In2)0.83 (In5)0.84(In5 / In2) 1.02 (In3)0.76 (In6)0.75(In6 / In3) 0,97 >10000 299 c 12 Total As / Total GaAs-O / Ga-O(As-O / Ga-O) / (Total As / Total Ga)Total As / Total GaAs-O / Ga-O 0.83 (In1)0.53 (In4)0.64(In4 / In1)0.51 (In1)0.28 (In4) 0.84 (In2)0.51 (In5)0.61(In5 / 1n2)0.60 (In2)0.27 (In5) 0.92 (In3)0.47 (In6)0.51(In6 / In3)0.71 (In3)0.27 (In6) 0,900,72 >10000 398 c 13 (As-O / Ga-O) / (Total As / Total Ga) 0.55(In4 / In1) 0.45(In5 / In2) 0.38(In6 / In3) >10000 553 c <bewertung>

[0164] According to Table 1, the quality of each of the epitaxial substrates from samples 1 to 6 was determined to be A or B, with each sample fulfilling all of the following conditions: In3 is 1.05 or more and 1.2 or less, In4, In5, and In6 are each 0.9 or more, In1 / In3 is 0.9 or more and 1.3 or less, and In4 / In1, In5 / In2, and In6 / In3 are each 0.7 or more and 1.1 or less. Conversely, according to Table 2, the quality of each of the epitaxial substrates from samples 11 to 13 was rated as C, since each of these substrates failed to meet at least one of the aforementioned relationships. [Second test]<Herstellung von GaAs Einkristallsubstraten> (Sample 7)

[0165] A GaAs single crystal substrate of sample 3 was obtained in the same way as in sample 2, except that in the preparation step a semi-insulating GaAs single crystal to which carbon atoms (C) had been added was cut and beveled to produce a GaAs single crystal substrate precursor with a diameter of 3 inch (100 mm) and a thickness of 350 µm. (Sample 8)

[0166] A GaAs single crystal substrate of sample 4 was obtained in the same way as in sample 2, except that in the preparation step a semi-insulating GaAs single crystal to which carbon atoms (C) had been added was cut and beveled to produce a GaAs single crystal substrate precursor with a diameter of 4 inch (100 mm) and a thickness of 350 µm. (Sample 9)

[0167] A GaAs single crystal substrate of sample 5 was obtained in the same way as in sample 3, except that in the preparation step a semi-insulating GaAs single crystal to which carbon atoms (C) had been added was cut and beveled to produce a GaAs single crystal substrate precursor with a diameter of 6 inch (150 mm) and a thickness of 675 µm. (Sample 10)

[0168] A GaAs single crystal substrate of sample 6 was obtained in the same way as in sample 3, except that in the preparation step a semi-insulating GaAs single crystal to which carbon atoms (C) had been added was cut and beveled to produce a GaAs single crystal substrate precursor with a diameter of 8 inch (200 mm) and a thickness of 675 µm. <Analyse der Gleichmäßigkeit der Hauptfläche von GaAs-Einkristallsubstraten> (Samples 7 and 8)

[0169] Five test pieces cut from each of the main faces of the GaAs single-crystal substrates of samples 7 and 8 were analyzed in the same manner as in [Analysis of GaAs single-crystal substrates by X-ray photoelectron spectroscopy] in the first test. Thus, the seventh integrated intensity ratio (In7) and the eighth integrated intensity ratio (In8) were determined, where the seventh integrated intensity ratio (In7) and the eighth integrated intensity ratio (In8) are each a ratio of the sum of the integrated intensities of As 5+ , the integrated intensity of As 3+ , the integrated intensity of As-Ga and the integrated intensity of metal-As to the sum of the integrated intensity of Ga + , the integrated intensity of Ga 3+ and the integrated intensity of Ga-As, which was obtained based on the XPS analysis performed under one of conditions 1 and 3. In addition, the ninth integrated intensity ratio (In9) and the tenth integrated intensity ratio (In10) were also obtained, where the ninth integrated intensity ratio (In9) and the tenth integrated intensity ratio (In10) are each a ratio of the sum of the integrated intensities of As. 5+ and the integrated intensity of As 3+ to the sum of the integrated intensity of Ga + and the integrated intensity of Ga 3+ are those obtained based on the XPS analysis, which was carried out under one of the corresponding conditions 1 and 3.

[0170] Next, the standard deviation / mean value of the eighth integrated intensity ratio (In8) was calculated from the standard deviation and mean value of the eighth integrated intensity ratio (In8). The standard deviation / mean value of R1 / R2 was also calculated from the standard deviation and mean value of R1 / R2, which is the ratio of ratio R1 (In9 / In7) to ratio R2 (In10 / In8), where ratio R1 is the ratio of the ninth integrated intensity ratio (In9) to the seventh integrated intensity ratio (In7), and ratio R2 (In10 / In8) is the ratio of the tenth integrated intensity ratio (In10) to the eighth integrated intensity ratio (In8).

[0171] Each of the five test pieces comprises a first measuring point P1, a second measuring point P2, a third measuring point P3, a fourth measuring point P4 and a fifth measuring point P5, which are in Fig. Table 4 shows the results. Furthermore, each of the five test pieces was placed in a high-resolution XPS analyzer to direct X-rays onto each of the first measurement points P1, second measurement points P2, third measurement points P3, fourth measurement points P4, and fifth measurement points P5. The results are presented in Tables 3 and 4. Table 3 shows In8, its standard deviation and mean value, R1 / R2, and its standard deviation and mean value in the GaAs single-crystal substrate of sample 7. Table 4 shows In8, its standard deviation and mean value, R1 / R2, and its standard deviation and mean value in the GaAs single-crystal substrate of sample 8. The smaller the standard deviation / mean value in Tables 3 and 4, the more uniform the property of the GaAs single-crystal substrate in the plane of the main surface. (Samples 9 and 10)

[0172] Nine test pieces, cut from each of the main faces of the GaAs single-crystal substrates of samples 9 and 10, were analyzed in the same manner as in [Analysis of GaAs single-crystal substrates by X-ray photoelectron spectroscopy] in the first test. Thus, an eleventh integrated intensity ratio (In11) and a twelfth integrated intensity ratio (In12) were obtained, where the eleventh integrated intensity ratio (In11) and the twelfth integrated intensity ratio (In12) each represent a ratio of a sum of an integrated intensity of As 5+ , an integrated intensity of As 3+ , an integrated intensity of As-Ga and an integrated intensity of the metal-As to a sum of an integrated intensity of Ga + , an integrated intensity of Ga 3+ and an integrated intensity of Ga-As obtained from the XPS analysis performed under one of conditions 1 and 3. In addition, a thirteenth integrated intensity ratio (In13) and a fourteenth integrated intensity ratio (In14) were also obtained, each of the thirteenth integrated intensity ratio (In13) and the fourteenth integrated intensity ratio (In14) being a ratio of a sum of an integrated intensity of As 5+ and an integrated intensity of As 3+ to a sum of an integrated intensity of Ga + and an integrated intensity of Ga 3+ is, which were obtained based on the XPS analysis, which was carried out under one of the corresponding conditions 1 and 3.

[0173] Next, the standard deviation / mean value of the twelfth integrated intensity ratio (In12) was calculated from the standard deviation and mean value of the twelfth integrated intensity ratio (In12). The standard deviation / mean value of R3 / R4 was also calculated from the standard deviation and mean value of R3 / R4, where R3 / R4 is the ratio of ratio R3 (In13 / In11) and ratio R4 (In14 / In12), where ratio R3 (In13 / In11) is a ratio of the thirteenth integrated intensity ratio (In13) to the eleventh integrated intensity ratio (In11), and ratio R4 (In14 / In12) is a ratio of the fourteenth integrated intensity ratio (In14) to the twelfth integrated intensity ratio (In12).

[0174] Each of the nine test pieces comprises a first measurement point P1, a second measurement point P2, a third measurement point P3, a fourth measurement point P4, a fifth measurement point P5, a sixth measurement point P6, a seventh measurement point P7, an eighth measurement point P8, and a ninth measurement point P9, as shown in Fig. Figure 5 is shown. Furthermore, each of the nine test pieces was placed in a high-resolution XPS analyzer to irradiate each of the first measurement points P1, second measurement points P2, third measurement points P3, fourth measurement points P4, fifth measurement points P5, sixth measurement points P6, seventh measurement points P7, eighth measurement points P8, and ninth measurement points P9 with X-rays. The results are shown in Tables 5 and 6. Table 5 shows In12, its standard deviation and mean value, R3 / R4, and its standard deviation and mean value in the GaAs single-crystal substrate of sample 9. Table 6 shows In12, its standard deviation and mean value, R3 / R4, and its standard deviation and mean value in the GaAs single-crystal substrate of sample 10. The smaller the standard deviation / mean value in Tables 5 and 6, the more uniform the property of the GaAs single-crystal substrate in the plane of the main surface. [Table 3] Table 3 Measuring point Coordinates(X,Y) In8 R1 / R2 600eV 85° P1 (0,0) 1,09 0.94 P2 (19,0) 1,07 0.85 P3 (0,19) 1,08 0.94 P4 (-19,0) 1,09 0.86 P5 (0,-19) 1,10 0.96 Average Standard deviation σσ / Average 1.09 0,91 0.011 0,051 0.010 0,056 [Table 4] Table 4 Measuring point Coordinates(X,Y) In8 R1 / R2 600eV 85° P1 (0,0) 1,09 0.95 P2 (25,0) 1,08 0.99 P3 (0,25) 1,08 0.99 P4 (25,0) 1,09 1.02 P5 (0,25) 1,07 0.85 Average Standard deviation σσ / Average 1.08 0,96 0.008 0,066 0.008 0,069 [Table 5] Table 5 Measuring point Coordinates(X,Y) In 12 R3 / R4 600eV 85° P1 (0,0) 1,06 0.99 P2 (37,5,0) 1,06 0.89 P3 (0,37,5) 1,08 0.90 P4 (-37,5,0) 1,06 1.00 P5 (0,-37,5) 1,10 0.95 P6 (65,0) 1,09 1.03 P7 (0,65) 1,09 1.02 P8 (-65,0) 1,07 1.02 P9 (0,-65) 1,09 0.89 Average Standard deviation σσ / Average 1,08 0,97 0,016 0,059 0,015 0,061 [Table 6] Table 6 Measuring point Coordinates(X,Y) In 12 R3 / R4 600eV 85° P1 (0,0) 1,08 0.96 P2 (50,0) 1,09 1.00 P3 (0,50) 1,06 0.86 P4 (-50,0) 1,08 1.02 P5 (0,-50) 1,09 1.10 P6 (90,0) 1,06 0.89 P7 (0,90) 1,06 0.89 P8 (-90,0) 1,05 0.99 P9 (0,-90) 1,09 0.95 Averages Standard deviation σσ / average 1,07 0,96 0,016 0,075 0.015 0.078 <bewertung>

[0175] According to Tables 3 and 4, in each of the GaAs single-crystal substrates of samples 7 and 8, the standard deviation / mean value of In8 satisfies the relationship standard deviation / mean value ≤ 0.01, and the standard deviation and mean value of R1 / R2 satisfies the relationship standard deviation / mean value ≤ 0.07. According to Tables 5 and 6, in each of the GaAs single-crystal substrates of samples 9 and 10, the standard deviation / mean value of In12 satisfies the relationship standard deviation / mean value ≤ 0.015, and the standard deviation and mean value of R3 / R4 satisfies the relationship standard deviation / mean value ≤ 0.078. This means that the property of each of the GaAs single-crystal substrates of samples 7 to 10 is sufficiently uniform in the plane of the principal surface.Since each of the GaAs single crystal substrates of samples 7 to 10 exhibits a high mirror surface property across its entire main surface, it is expected that epitaxial film with a reduced turbidity value can be formed on it.

[0176] So far, the embodiments and examples of the present disclosure have been explained, but it was originally expected that configurations of the embodiments and examples could be combined in a suitable manner.

[0177] The embodiments and examples disclosed herein are illustrative and in no way limiting. The scope of the present invention is defined by the terms of the claims, and not by the embodiments and examples described above, and is intended to encompass all modifications within the scope and meaning that correspond to the terms of the claims. List of reference symbols

[0178] 1 GaAs single crystal substrate; 1 m main surface; 10 X-ray generation system; 11 X-ray source; 12, 14 slit; 13 grating; 20 vacuum chamber; 30 electron spectrometer; 50 notch; 100 analysis system; LA As3d spectrum; LG Ga3d spectrum; L1 Ga 3+ -Spectrum; L2 Ga + -Spectrum; L3 Ga-As spectrum; L4 As 5+ -Spectrum; L5 As 3+ -Spectrum; L6 Metal-As spectrum; L7 As-Ga spectrum; P1 First measurement point; P2 Second measurement point; P3 Third measurement point; P4 Fourth measurement point; P5 Fifth measurement point; P6 Sixth measurement point; P7 Seventh measurement point; P8 Eighth measurement point; P9 Ninth measurement point; A1 to A9 Measurement target; S100 Preparation step; S200 Cleaning step; S210 Surface polishing step; S220 First alkaline cleaning step; S230 Acid cleaning step; S240 Second alkaline cleaning step; S250 Heat treatment step; S300 Epitaxial film formation step. 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] JP 2008-300747

[0002] Cited non-patent literature

[0000] Method of Estimating Inelastic Mean Free Path of Electrons by Tpp-2M Formula", Journal of Surface Analysis, Volume 1, No. 2, 1995

[0065] Kazuhiro Yoshihara: Journal of the Vacuum Society of Japan, 2013, Volume 56, No. 6, pp. 243 to 247

[0074] JJ Yeh, “Atomic Calculation of Photoionization Cross-Sections and Asymmetry Parameters”, Gordon and Breach Science Publishers, Langhorne, PE (USA), 1993

[0088] JJ Yeh and I. Lindau, "Atomic Data and Nuclear Data Tables", 32, 1-155 (1985

[0088] Trade name: “R3000” from Scienta Omicron

[0160] < / bewertung> < / bewertung> < / epitaxieschicht> < / durchmesser>

Claims

[1] A gallium arsenide single crystal substrate having a main surface having a circular shape, wherein the gallium arsenide single crystal substrate has a first integrated intensity ratio, a second integrated intensity ratio, a third integrated intensity ratio, a fourth integrated intensity ratio, a fifth integrated intensity ratio and a sixth integrated intensity ratio, wherein the first integrated intensity ratio and the fourth integrated intensity ratio are each obtained by determining the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of an X-ray photoelectron spectroscopy in which X-ray radiation is directed towards a center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°; wherein the second integrated intensity ratio and the fifth integrated intensity ratio are each obtained by determining the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of an X-ray photoelectron spectroscopy in which X-ray radiation is directed towards the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 45°; wherein the third integrated intensity ratio and the sixth integrated intensity ratio are each obtained by determining the spectra of the detection intensities of 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of an X-ray photoelectron spectroscopy in which X-ray radiation is directed towards the center of the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°; The first integrated intensity ratio, the second integrated intensity ratio, and the third integrated intensity ratio are a ratio of the sum of an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide, an integrated intensity of an arsenic element present as gallium arsenide, and an integrated intensity of an arsenic element present as metallarsene to a sum of an integrated intensity of a gallium element present as digallium monoxide, an integrated intensity of a gallium element present as digallium trioxide, and an integrated intensity of a gallium element present as gallium arsenide. The fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are a ratio of the sum of an integrated intensity of the arsenic element present as diarsene pentoxide and an integrated intensity of the arsenic element present as diarsene trioxide to the sum of an integrated intensity of the gallium element present as digallium monoxide and an integrated intensity of the gallium element present as digallium trioxide. the third integrated intensity ratio is 1.05 or more and 1.2 or less, the fourth integrated intensity ratio, the fifth integrated intensity ratio and the sixth integrated intensity ratio each have a value of 0.9 or higher, a ratio of the first integrated intensity ratio to the third integrated intensity ratio is 0.9 or more and 1.3 or less, and a ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, a ratio of the fifth integrated intensity ratio to the second integrated intensity ratio, and a ratio of the sixth integrated intensity ratio to the third integrated intensity ratio is 0.7 or more and 1.1 or less. [2] The gallium arsenide single crystal substrate according to claim 1, wherein the ratio of the first integrated intensity to the third integrated intensity is 0.95 or more and 1.2 or less. [3] The gallium arsenide single crystal substrate according to claim 1 or 2, wherein the third integrated intensity ratio is 1.05 or more and 1.1 or less. [4] The gallium arsenide single crystal substrate according to any one of claims 1 to 3, wherein the fourth integrated intensity ratio, the fifth integrated intensity ratio and the sixth integrated intensity ratio are each 1.2 or less. [5] The gallium arsenide single crystal substrate according to any one of claims 1 to 4, wherein the ratios of the fourth integrated intensity ratio to the first integrated intensity ratio, the fifth integrated intensity ratio to the second integrated intensity ratio and the sixth integrated intensity ratio to the third integrated intensity ratio are each 0.75 or more and 1.05 or less. [6] The gallium arsenide single crystal substrate according to any one of claims 1 to 5, wherein the gallium arsenide single crystal substrate has a diameter of 75 mm or more and 205 mm or less. [7] The gallium arsenide single crystal substrate according to any one of claims 1 to 6, wherein the gallium arsenide single crystal substrate has a diameter of 75 mm or more and less than 150 mm, the gallium arsenide single crystal substrate exhibits a seventh integrated intensity ratio, an eighth integrated intensity ratio, a ninth integrated intensity ratio, and a tenth integrated intensity ratio. wherein the seventh and ninth integrated intensity ratios are each obtained by determining the spectra of the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed at five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°; wherein the eighth integrated intensity ratio and the tenth integrated intensity ratio are each obtained by determining the spectra of the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of an X-ray photoelectron spectroscopy in which X-ray radiation is directed at five measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°; The seventh and eighth integrated intensity ratios are a ratio of a sum of an integrated intensity of the arsenic element present as diarsene pentoxide, an integrated intensity of the arsenic element present as diarsene trioxide, an integrated intensity of the arsenic element present as gallium arsenide, and an integrated intensity of the arsenic element present as metallarsene to a sum of an integrated intensity of the gallium element present as digallium monoxide and an integrated intensity of the gallium element present as gallium arsenide. the ninth integrated intensity ratio and the tenth integrated intensity ratio are a ratio of the sum of an integrated intensity of the arsenic element present as diarsene pentoxide and an integrated intensity of the arsenic element present as diarsene trioxide to a sum of an integrated intensity of the gallium element present as digallium monoxide and an integrated intensity of the gallium element present as digallium trioxide. A standard deviation and an average value of the eighth integrated intensity ratio satisfy a relationship of standard deviation / average value ≤ 0.01, a standard deviation and a mean value of R1 / R2 satisfy a relationship of standard deviation / mean value ≤ 0.07, where R1 / R2 is a ratio of a ratio R1 and a ratio R2, where the ratio R1 is a ratio of the ninth integrated intensity ratio to the seventh integrated intensity ratio and the ratio R2 is a ratio of the tenth integrated intensity ratio to the eighth integrated intensity ratio, and if the diameter is represented by D and two axes, each passing through the center of the main surface and lying on the main surface and being orthogonal to each other, are defined as the X-axis and Y-axis, the coordinates (X, Y) of the five measurement points on the X-axis and the Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0) and (0, -D / 4) and the units of D and of X and Y in the coordinates (X, Y) are mm. [8] The gallium arsenide single crystal substrate according to any one of claims 1 to 6, wherein the gallium arsenide single crystal substrate has a diameter of 150 mm or more and 205 mm or less, the gallium arsenide single crystal substrate exhibits an eleventh integrated intensity ratio, a twelfth integrated intensity ratio, a thirteenth integrated intensity ratio, and a fourteenth integrated intensity ratio. wherein the eleventh and thirteenth integrated intensity ratios are each obtained by determining the spectra of the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed at nine measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 30°, The twelfth and fourteenth integrated intensity ratios are each obtained by determining the spectra of the detection intensities of the 3d electrons of gallium and arsenic with respect to the binding energy of a photoelectron emitted outwards from the gallium arsenide single crystal substrate on the basis of X-ray photoelectron spectroscopy, in which X-ray radiation is directed onto nine measurement points on the main surface under conditions of an X-ray incident energy of 600 eV and a photoelectron exit angle of 85°. the eleventh integrated intensity ratio and the twelfth integrated intensity ratio are a ratio of a sum of an integrated intensity of the arsenic element present as diarsene pentoxide, an integrated intensity of the arsenic element present as diarsene trioxide, an integrated intensity of the arsenic element present as gallium arsenide and an integrated intensity of the arsenic element present as metallarsene to a sum of an integrated intensity of the gallium element present as digallium monoxide, an integrated intensity of the gallium element present as digallium trioxide and an integrated intensity of the gallium element present as gallium arsenide, the thirteenth integrated intensity ratio and the fourteenth integrated intensity ratio are a ratio of the sum of an integrated intensity of the arsenic element present as diarsene pentoxide and an integrated intensity of the arsenic element present as diarsene trioxide to a sum of an integrated intensity of the gallium element present as digallium monoxide and an integrated intensity of the gallium element present as digallium trioxide. A standard deviation and an average value of the twelfth integrated intensity ratio satisfy a relationship standard deviation / average value ≤ 0.015, a standard deviation and a mean value of R3 / R4 satisfy a relationship of standard deviation / mean value ≤ 0.078, where R3 / R4 is a ratio of a ratio R3 and a ratio R4, where the ratio R3 is a ratio of the thirteenth integrated intensity ratio to the eleventh integrated intensity ratio and the ratio R4 is a ratio of the fourteenth integrated intensity ratio to the twelfth integrated intensity ratio, and if the diameter is represented by D and two axes, each passing through the center of the main surface, each lie on the main surface and are orthogonal to each other, are defined as the X-axis and Y-axis, the coordinates (X, Y) of the nine measurement points on the X-axis and the Y-axis are (0, 0), (D / 4, 0), (0, D / 4), (-D / 4, 0), (0, -D / 4), (D / 2-1 0, 0), (0, D / 2-10), (-(D / 2-10), 0) and (0, -(D / 2-10)), and the units of D and X and Y in the coordinates (X, Y) are mm. [9] The gallium arsenide single crystal substrate according to any one of claims 1 to 8, wherein the gallium arsenide single crystal substrate has an epitaxial layer arranged on the main surface, a maximum turbidity value of a surface of the epitaxial layer is 350 ppm or less and an average value of the turbidity of the surface of the epitaxial layer is 2.5 ppm or less. [10] A method for producing a gallium arsenide single crystal substrate having a circular main surface, comprising: Preparation of a gallium arsenide single-crystal substrate precursor with a circular surface; and Obtaining the gallium arsenide single crystal substrate from the gallium arsenide single crystal substrate precursor, wherein The preservation includes Forming the surface of the gallium arsenide single-crystal substrate precursor into a polished surface by polishing the surface, Forming the polished surface into an alkali-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid, Forming the alkali-cleaned surface into an acid-cleaned surface by cleaning the alkali-cleaned surface by immersing the alkali-cleaned surface in a first acid cleaning fluid containing 0.3 ppm by mass or more and 0.5% by mass or less of a first acid, Forming the acid-cleaned surfaces into a second acid-cleaned surface by cleaning the acid-cleaned surface by supplying a second acid cleaning fluid containing 0.3 ppm by mass or more and 0.5% by mass or less of a second acid, at a flow rate of 0.1 l / min or more and 5 l / min or less for 30 seconds or more and 5 minutes or less, while the acid-cleaned surface is rotated circumferentially at a speed of 1000 rpm or more, and Forming the second acid-cleaned surface into the main surface by performing a heat treatment on the second acid-cleaned surface in an inert gas atmosphere for 1 minute or longer and 30 minutes or less under atmospheric pressure and a temperature of 150 °C or more and 300 °C or less, wherein the first acid contained in the first acid cleaning solution is at least one selected from the group consisting of hydrofluoric acid, hydrochloric acid, nitric acid and nitrous acid, and The second acid contained in the second acid cleaning solution is at least one selected from a group consisting of hydrofluoric acid, hydrochloric acid, nitric acid and nitrous acid. [11] The method for producing a gallium arsenide single crystal substrate according to claim 10, comprising forming an epitaxial layer on the main surface. [12] The gallium arsenide single crystal substrate according to claim 2, wherein the third integrated intensity ratio is 1.05 or more and 1.1 or less, the fourth integrated intensity ratio, the fifth integrated intensity ratio, and the sixth integrated intensity ratio are 1.2 or less and the ratio of the fourth integrated intensity ratio to the first integrated intensity ratio, the fifth integrated intensity ratio to the second integrated intensity ratio, and the sixth integrated intensity ratio to the third integrated intensity ratio is 0.75 or more and 1.05 or less.

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