Gallium arsenide single crystal substrate and method for its preparation

Abstract

A gallium arsenide single-crystal substrate has a main surface with a circular shape and features R1, R2, R3, R4, R5, and R6, each of which is a first integrated intensity ratio. The first integrated intensity ratio is obtained by determining a spectrum of the detection intensity of a 3d electron of arsenic with respect to a 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 applied centrally to the main surface under specific conditions. The first integrated intensity ratio is a ratio of an integrated intensity of an arsenic element present as diarsene pentoxide to the sum of the integrated intensity of the arsenic element present as diarsene pentoxide and the integrated intensity of an arsenic element present as arsenic trioxide.an integrated intensity of an arsenic element present as gallium arsenide and an integrated intensity of an arsenic element present as metallarsene, and wherein R2 and / or R3 and / or R4 is the largest among R1, R2, R3, R4, R5 and R6.

Description

Technical field

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

[0002] Japanese patent 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 interface layer with a thickness of 3 Å or less on its surface. Japanese patent no. 2008-300747 (PTL 2) proposes providing a GaAs wafer that is cleaned by at least one thermal cleaning of the surface of a GaAs single-crystal substrate to such an extent that impurities and oxide on its surface can be removed by thermal cleaning. List of cited writings Patent specifications PTL 1: Published Japanese patent address no. 06-045318 PTL 2: Published Japanese Patent No. 2008-300747 Overview of the invention

[0003] A gallium arsenide single-crystal substrate according to the present disclosure is a gallium arsenide single-crystal substrate with a major surface having a circular shape. The gallium arsenide single-crystal substrate has R1, R2, R3, R4, R5, and R6, each of which is a first integrated intensity ratio. The first integrated intensity ratio is obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a binding energy of a photoelectron emitted outward from the gallium arsenide single-crystal substrate based on X-ray photoelectron spectroscopy in which X-ray radiation is applied to a center of the major surface under each of the specific conditions described below.The first integrated intensity ratio is the ratio of the integrated intensity of an arsenic element present as diarsene pentoxide to the sum of the integrated intensity of the arsenic element present as diarsene pentoxide, the integrated intensity of an arsenic element present as diarsene trioxide, the integrated intensity of an arsenic element present as gallium arsenide, and the integrated intensity of an arsenic element present as metal arsenic. R1 is obtained by performing X-ray photoelectron spectroscopy under condition 1 described below. R2 is obtained by performing X-ray photoelectron spectroscopy under condition 2 described below. R3 is obtained by performing X-ray photoelectron spectroscopy under condition 3 described below. R4 is obtained by performing X-ray photoelectron spectroscopy under condition 4 described below.R5 is obtained by performing X-ray photoelectron spectroscopy under condition 5 described below. R6 is obtained by performing X-ray photoelectron spectroscopy under condition 6 described below. A relationship is satisfied in which at least one of the values ​​R2, R3, and R4 is the largest among the values ​​R1, R2, R3, R4, R5, and R6.

[0004] Condition 1: X-ray incidence energy of 150 eV and photoelectron exit angle of 30°.

[0005] Condition 2: X-ray incidence energy of 150 eV and photoelectron exit angle of 45°.

[0006] Condition 3: X-ray incidence energy of 150 eV and photoelectron exit angle of 85°.

[0007] Condition 4: X-ray incidence energy of 600 eV and photoelectron exit angle of 30°.

[0008] Condition 5: X-ray incidence energy of 600 eV and photoelectron exit angle of 45°.

[0009] Condition 6: X-ray incidence energy of 600 eV and photoelectron exit angle of 85°.

[0010] 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 principal surface having a circular shape. The process includes: preparing a gallium arsenide single-crystal substrate precursor having a surface having a circular shape; and obtaining the gallium arsenide single-crystal substrate from the gallium arsenide single-crystal substrate precursor. Obtaining the substrate 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 alkaline-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid.Forming the alkaline-cleaned surface into a first acid-cleaned surface by cleaning the alkaline-cleaned surface with an acid-cleaning liquid containing 0.3% by mass or more and 1% by mass or less of a first acid; forming the first acid-cleaned surface into a second acid-cleaned surface by immersing the first acid-cleaned surface in a second acid containing more than 0.5% by mass and 1% by mass or less for 1 minute or longer; and forming the second acid-cleaned surface into the main surface by performing a heat treatment of the second acid-cleaned surface in an inert gas atmosphere under conditions of 100°C or higher and 200°C or lower for 1 minute or longer and 30 minutes or less. The second acid contains hydrofluoric acid and / or hydrochloric acid and / or nitric acid and / or nitrous acid. Brief description of drawings [ Fig. 1] Fig. Figure 1 is an exemplary diagram showing a relationship between an analysis depth (horizontal axis) of a main surface of a gallium arsenide single crystal substrate according to the present embodiment and a ratio (vertical axis) of each an integrated intensity of an arsenic element present as diarsene pentoxide, an integrated intensity of an arsenic element present as diarsene trioxide and an integrated intensity of an arsenic element present as metal arsenic to an integrated intensity of the total arsenic elements. [ Fig. 2] Fig. Figure 2 is an explanatory diagram that schematically illustrates the setup of an analysis system using X-ray photoelectron spectroscopy. [ Fig. 3] Fig.Figure 3 is a diagram showing an exemplary As-3d spectrum after background correction obtained on the basis of X-ray photoelectron spectroscopy in which X-ray radiation was irradiated onto the center of a main surface of a gallium arsenide single crystal substrate according to the present embodiment. [ Fig. 4] Fig. Figure 4 is an explanatory illustration showing five measuring points which, in the present embodiment, are fixed on a gallium arsenide single crystal substrate with a diameter greater than or equal to 75 mm and less than or equal to 150 mm. [ Fig. 5] Fig. Figure 5 is an explanatory illustration showing nine measuring points which, in the present embodiment, are fixed on a gallium arsenide single crystal substrate with a diameter greater than or equal to 150 mm and less than or equal to 205 mm. [ Fig. 6] Fig.Figure 6 is a flowchart showing a process for preparing the gallium arsenide single crystal substrate according to the present embodiment. Detailed description [Problem to be solved by the present disclosure]

[0011] One method used to evaluate the reflective surface properties (i.e., the presence or absence of a height difference) of an epitaxial layer is turbidity, and it is known that an increase in the turbidity value is associated with a deterioration of the component properties. Turbidity refers to the amount of scattered light that is scattered due to surface irregularities and fine defects and foreign matter present on the surface when laser light is applied to the surface of the epitaxial layer. Turbidity is expressed as the ratio of the amount of scattered light to the amount of laser light incident on the surface. The turbidity is given in parts per million (ppm). It is assumed that the lower the turbidity value, the better the surface reflectivity and the smaller the height difference.The height difference arises, for example, from a stacking fault that develops during the growth of an epitaxial layer on the 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 surface properties in order to reduce the haze value.

[0012] It was expected that the thermal purification described above would serve as one of the means to achieve such a GaAs single-crystal substrate with a main surface exhibiting high mirror surface properties by removing an oxide layer from the main surface. However, in some cases, it is necessary to further reduce the turbidity of the epitaxial layer grown on the main surface of the GaAs single-crystal substrate, which was formed by thermal purification to create a mirror surface, as is the case, for example, in PTL 1.

[0013] In view of the foregoing, it is an object of the present disclosure to provide: a gallium arsenide single crystal substrate for improving the component properties 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]

[0014] According to the present disclosure, it is possible to provide: a gallium arsenide single-crystal substrate for improving component properties 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 embodiments]

[0015] First, an overview of an embodiment of the present disclosure is given. To solve the problem described above, the inventors, after careful investigation, prepared the present disclosure. That is, the inventors aimed to obtain a primary surface with pronounced mirror-like surface properties in a gallium arsenide single-crystal substrate by carrying out a novel purification process on a gallium arsenide single-crystal substrate precursor having a circular surface and cut from a gallium arsenide single crystal. In particular, in addition to the conventional liquid-phase treatment using an acidic solution and / or an alkaline solution, an acid treatment using a second acid and a heat treatment were carried out as innovations.As a result, it was found that the oxide layer can be effectively removed from the GaAs single-crystal substrate obtained by the new purification process by suppressing the progression of oxidation of the oxide layer over time through thermal purification. In this way, a GaAs single-crystal substrate with a main surface exhibiting good mirror surface properties can be obtained, leading to a GaAs single-crystal substrate on which an epitaxial layer with a reduced turbidity value can be formed, thus providing a solution in the present disclosure.

[0016] Next, embodiments of the present disclosure will be listed and described.

[0017] [1] A gallium arsenide single-crystal substrate according to one embodiment of the present disclosure is a gallium arsenide single-crystal substrate having a main surface having a circular shape. The gallium arsenide single-crystal substrate has R1, R2, R3, R4, R5 and R6, each of which is a first integrated intensity ratio. The first integrated intensity ratio is obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a 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 applied centrally to the main surface under each of the specific conditions described below.The first integrated intensity ratio is the ratio of the integrated intensity of an arsenic element present as diarsene pentoxide to the sum of the integrated intensity of the arsenic element present as diarsene pentoxide, the integrated intensity of an arsenic element present as diarsene trioxide, the integrated intensity of an arsenic element present as gallium arsenide, and the integrated intensity of an arsenic element present as metal arsenic. R1 is obtained by performing X-ray photoelectron spectroscopy under condition 1 described below. R2 is obtained by performing X-ray photoelectron spectroscopy under condition 2 described below. R3 is obtained by performing X-ray photoelectron spectroscopy under condition 3 described below. R4 is obtained by performing X-ray photoelectron spectroscopy under condition 4 described below.R5 is obtained by performing X-ray photoelectron spectroscopy under condition 5 described below. R6 is obtained by performing X-ray photoelectron spectroscopy under condition 6 described below. A relationship is satisfied in which at least one of the values ​​R2, R3, and R4 is the largest among the values ​​R1, R2, R3, R4, R5, and R6.

[0018] Condition 1: X-ray incidence energy of 150 eV and photoelectron exit angle of 30°.

[0019] Condition 2: X-ray incidence energy of 150 eV and photoelectron exit angle of 45°.

[0020] Condition 3: X-ray incidence energy of 150 eV and photoelectron exit angle of 85°.

[0021] Condition 4: X-ray incidence energy of 600 eV and photoelectron exit angle of 30°.

[0022] Condition 5: X-ray incidence energy of 600 eV and photoelectron exit angle of 45°.

[0023] Condition 6: X-ray incidence energy of 600 eV and photoelectron exit angle of 85°.

[0024] The gallium arsenide single crystal substrate with such a property can have a main surface with a very good 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.

[0025] [2] R1, R2, R3, R4, R5 and R6 are each preferably greater than or equal to 0.05 and less than or equal to 0.55. This allows the oxide layer to be removed more effectively by thermal cleaning.

[0026] [3] R6 is preferably greater than or equal to 0.1 and less than 0.2. This allows the oxide layer to be removed more effectively by thermal cleaning.

[0027] [4] R1 is preferably greater than or equal to 0.2 and less than 0.35. This allows the oxide layer to be removed more effectively by thermal cleaning.

[0028] [5] The gallium arsenide single-crystal substrate preferably has a diameter greater than or equal to 75 mm and less than or equal to 205 mm. Thus, the gallium arsenide single-crystal substrate with a diameter greater than or equal to 75 mm and less than or equal to 205 mm can be provided with a main surface having very good mirror surface properties, allowing an epitaxial layer with a reduced turbidity value to be formed on it.

[0029] [6] The gallium arsenide single-crystal substrate preferably has the following feature. The gallium arsenide single-crystal substrate has a diameter greater than or equal to 75 mm and less than 150 mm. The gallium arsenide single-crystal substrate has RS1, RS2, RS3, RS4, RS5, and RS6, each of which is a second integrated intensity ratio. The gallium arsenide single-crystal substrate has a standard deviation and a mean value for RS1, RS2, RS3, RS4, RS5, and RS6, respectively. The standard deviation and mean of RS1, RS2, RS3, RS4, RS5 and RS6 are obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a 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 irradiated onto five measurement points on the main surface under each of the conditions 1, 2, 3, 4, 5 and 6.The standard deviation and mean of RS1, RS2, RS3, RS4, RS5, and RS6 are the standard deviation and mean of the ratio of the integrated intensity of arsenic element present as diarsene pentoxide to the sum of the integrated intensity of arsenic element present as diarsene pentoxide, arsenic element present as diarsene trioxide, arsenic element present as gallium arsenide, and arsenic element present as metallosine. The ratio of the standard deviation of RS1 to the mean of RS1 is less than or equal to 0.1. The ratio of the standard deviation of RS2 to the mean of RS2 is less than or equal to 0.1. The ratio of the standard deviation of RS3 to the mean of RS3 is less than or equal to 0.1. The ratio of the standard deviation of RS4 to the mean of RS4 is less than or equal to 0.2.The ratio of the standard deviation of RS5 to the mean of RS5 is less than or equal to 0.2. The ratio of the standard deviation of RS6 to the mean of RS6 is less than or equal to 0.11. If the diameter is denoted as 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, 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, respectively, X and Y in the 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 greater than or equal to 75 mm and less than or equal to 150 mm, it is possible to obtain a main surface with very good mirror surface properties, so that an epitaxial layer with a reduced turbidity value can be formed on it.

[0030] [7] The gallium arsenide single-crystal substrate preferably has the following feature. The gallium arsenide single-crystal substrate has a diameter greater than or equal to 150 mm and less than or equal to 205 mm. The gallium arsenide single-crystal substrate has RT1, RT2, RT3, RT4, RT5, and RT6, each of which is a third integrated intensity ratio. The gallium arsenide single-crystal substrate has a standard deviation and a mean value for each of RT1, RT2, RT3, RT4, RT5, and RT6.The standard deviation and mean of RT1, RT2, RT3, RT4, RT5 and RT6 are obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a 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 irradiated onto each of five measurement points on the main surface under each of the conditions 1, 2, 3, 4, 5 and 6.The standard deviation and mean of RT1, RT2, RT3, RT4, RT5, and RT6 are the standard deviation and mean of the ratio of the integrated intensity of the arsenic element present as diarsene pentoxide to the sum of the integrated intensity of the arsenic element present as diarsene pentoxide, the integrated intensity of the arsenic element present as diarsene trioxide, the integrated intensity of the arsenic element present as gallium arsenide, and the integrated intensity of the arsenic element present as metallosine. The ratio of the standard deviation of RT1 to the mean of RT1 is less than or equal to 0.1. The ratio of the standard deviation of RT2 to the mean of RT2 is less than or equal to 0.1. The ratio of the standard deviation of RT3 to the mean of RT3 is less than or equal to 0.2. The ratio of the standard deviation of RT4 to the mean of RT4 is less than or equal to 0.2.The ratio of the standard deviation of RT5 to the mean of RT5 is less than or equal to 0.1. The ratio of the standard deviation of RT6 to the mean of RT6 is less than or equal to 0.2. If the diameter is denoted as D, and two axes, each passing through the center of the main surface, lying on the main surface and 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, respectively, X and Y in the coordinates (X, Y) are mm.By effectively removing the oxide layer by thermal cleaning on the gallium arsenide single crystal substrate with a diameter greater than or equal to 150 mm and less than or equal to 205 mm, a main surface with very good mirror surface properties can be obtained, allowing an epitaxial layer with a reduced turbidity value to be formed on it.

[0031] [8] Preferably, the gallium arsenide single-crystal substrate has an epitaxial layer arranged on the main surface, wherein the maximum turbidity value of a surface of the epitaxial layer is less than or equal to 350 ppm and the mean turbidity value of the surface of the epitaxial layer is less than or equal to 2.5 ppm. Thus, it is possible to provide a gallium arsenide single-crystal substrate having a main surface on which the epitaxial layer is formed with a reduced turbidity value.

[0032] [9] 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 major surface having a circular shape. The method comprises: preparing a gallium arsenide single-crystal substrate precursor having a surface having a circular shape; and obtaining the gallium arsenide single-crystal substrate from the gallium arsenide single-crystal substrate precursor. Obtaining 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 alkaline-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid,Forming the alkaline-cleaned surface into a first acid-cleaned surface by cleaning the alkaline-cleaned surface with an acid-cleaning liquid containing 0.3 ppm by mass or more and 1% by mass or less of a first acid; forming the first acid-cleaned surfaces into a second acid-cleaned surface by immersing the first acid-cleaned surfaces in more than 0.5% by mass and 1% by mass or less of a second acid for 1 minute or longer.and the formation of 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 under conditions of 100 °C or higher and 200 °C or lower for 1 minute or longer and 30 minutes or less. The second acid contains hydrofluoric acid and / or hydrochloric acid and / or nitric acid and / or nitrous acid. With this manufacturing process, it is possible to obtain a gallium arsenide single-crystal substrate with a main surface whose oxide film can be effectively removed by thermal cleaning.

[0033]

[10] Preferably, the method comprises forming an epitaxial layer on the main surface. In this way, an epitaxial layer with a reduced turbidity value can be formed on the main surface. [Details of embodiments]

[0034] 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.

[0035] In this description, the expression “A to B” denotes a range from lower to upper limits (i.e., greater than or equal to A and less than or equal to B), 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. Furthermore, where in this description a compound or the like is expressed 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.

[0036] In this description, the “main surface” of a gallium arsenide single-crystal substrate refers to each of the two circular surfaces of the substrate. If at least one of the two surfaces of the gallium arsenide single-crystal substrate satisfies the scope of the claims as defined in this disclosure, the gallium arsenide single-crystal substrate is within the scope of the present invention. An epitaxial layer may be arranged on the “main surface” of the gallium arsenide single-crystal substrate. Furthermore, in this description, the term “plane” in the expressions “in the plane” or “in the surface” means the “main surface.” 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 the diameter is approximately 150 mm (about 145 to 155 mm) or 6 inches. If the diameter is specified as "200 mm," this means 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 instrument, such as a caliper.

[0037] 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, which is normally expressed by a '-' (line) above a number, is expressed in this description by a minus sign before the number. [Gallium arsenide single crystal substrate]

[0038] A gallium arsenide single-crystal substrate (GaAs single-crystal substrate) according to the present embodiment is a GaAs single-crystal substrate with a main surface that is circular or has a circular shape. The GaAs single-crystal substrate has R1, R2, R3, R4, R5, and R6, each of which is a first integrated intensity ratio. The first integrated intensity ratio is obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a 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 applied centrally to the main surface under the specific conditions described below. The first integrated intensity ratio is a ratio of the integrated intensity of an arsenic (As) element (hereinafter referred to simply as "As"). s+“ designated), which exists as diarsene pentoxide (As2O5), to the sum of the integrated intensity of the As element (As 5+ ), which exists as As2O5, an integrated intensity of an As element (hereinafter also referred to as "As" for the sake of simplicity). 3+R1 is obtained by performing X-ray photoelectron spectroscopy under condition 1 described below. R2 is obtained by performing X-ray photoelectron spectroscopy under condition 2 described below. R3 is obtained by performing X-ray photoelectron spectroscopy under condition 3 described below. R4 is obtained by performing X-ray photoelectron spectroscopy under condition 4 described below. R5 is obtained by performing X-ray photoelectron spectroscopy under condition 5 described below.R6 is obtained by performing X-ray photoelectron spectroscopy under the condition described below. A relationship in which at least one of the values ​​R2, R3, and R4 is the largest among the values ​​R1, R2, R3, R4, R5, and R6 is satisfied.

[0039] Condition 1: X-ray incidence energy of 150 eV and photoelectron exit angle of 30°.

[0040] Condition 2: X-ray incidence energy of 150 eV and photoelectron exit angle of 45°.

[0041] Condition 3: X-ray incidence energy of 150 eV and photoelectron exit angle of 85°.

[0042] Condition 4: X-ray incidence energy of 600 eV and photoelectron exit angle of 30°.

[0043] Condition 5: X-ray incidence energy of 600 eV and photoelectron exit angle of 45°.

[0044] Condition 6: X-ray incident energy of 600 eV and photoelectron exit angle of 85°.

[0045] An oxide layer can be effectively removed from the GaAs single-crystal substrate with this property by thermal purification, allowing the GaAs single-crystal substrate to exhibit a main surface with very good mirror-like surface properties. Therefore, an epitaxial layer with a reduced turbidity value can be formed on the GaAs single-crystal substrate. <Hauptfläche>

[0046] The GaAs single-crystal substrate has a primary surface with the circular shape described above. In this description, the term "circular shape," referring to the shape of the primary surface, includes not only a geometric circle but also a shape where the primary surface is not a geometric circle due to the formation of at least one notch, one orientation flattening (hereinafter referred to as "OF"), and one index flattening (hereinafter referred to as "IF"). That is, the "shape when the primary surface is not a geometric circle" refers to a shape where the length of a line segment extending from any point on the notch, OF, and IF to the center of the primary surface is the shortest among the line segments extending from any point on the outer circumference of the primary surface to the center of the primary surface.In other words, in the present description, the principal surface is described as "circular" based on the shape that existed before the formation of the notch, 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 circular shape prior to the formation of the notch, OF, IF, and the like. 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 shape of the GaAs single crystal prior to its cutting as a 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 each extend from a 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. <Röntgen-Photoelektronenspektroskopie (XPS) unter Verwendung von Synchrotronstrahlung>

[0047] 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 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 types, abundances, chemical bonding states, and the like of the elements present on the surface of the sample.

[0048] When the main surface of a GaAs single-crystal substrate is examined using XPS, the analysis is often performed with X-rays at an energy of approximately 1.487 keV. However, when using X-rays at this energy and a photoelectron exit angle of 30°, information about the state of the main surface of the GaAs single-crystal substrate is obtained as an average over a region extending from the main surface to a depth of approximately 5 nm. This region corresponds to about 20 atomic layers when converted to atomic layers. Therefore, it is difficult to analyze the state of the main surface of the GaAs single-crystal substrate with high accuracy using XPS.Furthermore, if X-rays with an incident energy of approximately 1.487 keV are used and the photoelectron exit angle in the XPS is modified to obtain information about the state of the main surface of the GaAs single-crystal substrate, the measurement error with respect to the angle becomes too large. This is compounded by the low ionization efficiency of the photoelectron intensity, resulting in a significant measurement error, which also makes high-precision analysis difficult.

[0049] On the other hand, in the present disclosure, XPS is carried out under conditions (hereinafter also referred to as “specific conditions”) in which X-rays with an X-ray incident energy of 150 eV or 600 eV are used and the photoelectron exit angle is set to 30°, 45° or 85°, as shown in conditions 1 to 6 below, the condition of the main surface of the GaAs single crystal substrate can be analyzed.

[0050] Condition 1: X-ray incidence energy of 150 eV and photoelectron exit angle of 30°.

[0051] Condition 2: X-ray incidence energy of 150 eV and photoelectron exit angle of 45°.

[0052] Condition 3: X-ray incidence energy of 150 eV and photoelectron exit angle of 85°.

[0053] Condition 4: X-ray incidence energy of 600 eV and photoelectron exit angle of 30°.

[0054] Condition 5: X-ray incidence energy of 600 eV and photoelectron exit angle of 45°.

[0055] Condition 6: X-ray incidence energy of 600 eV and photoelectron exit angle of 85°.

[0056] When the X-ray incidence energy is set to 150 eV and the photoelectron exit angle to 30° (condition 1), information about the state of the main surface of the GaAs single-crystal substrate can be determined as an average value in a region from the main surface to a depth of approximately 0.90 nm. When the X-ray incidence energy is set to 150 eV and the photoelectron exit angle to 45° (condition 2), information about the state of the main surface of the GaAs single-crystal substrate can be determined as an average value in a region from the main surface to a depth of approximately 1.28 nm. If the X-ray incident energy is set to 150 eV and the photoelectron exit angle to 85° (condition 3), the information about the state of the main surface of the GaAs single crystal substrate can be determined as an average value in a range from the main surface to a depth of about 1.80 nm.

[0057] When the X-ray incidence energy is set to 600 eV and the photoelectron exit angle to 30° (condition 4), information about the state of the main surface of the GaAs single-crystal substrate can be obtained as an average value in 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° (condition 5), information about the state of the main surface of the GaAs single-crystal substrate is obtained as an average value in a region from the main surface to a depth of approximately 3.18 nm. When the X-rays are set to 600 eV and the photoelectron exit angle to 85° (condition 6), information about the state of the main surface of the GaAs single-crystal substrate is obtained as an average value in a region from the main surface to a depth of approximately 4.48 nm.This means that the area 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 roughly every first to third atomic layer. Thus, the state of the main surface can be analyzed more accurately than with the prior art.

[0058] 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 focused on precisely controlling the environment of an interface (i.e., the surface) using synchrotron radiation, as previously described, via XPS.The inventors investigated the region at a depth of approximately 1 to 2 nm from the main surface of the GaAs single-crystal substrate, between the oxide layer covering the top of the main surface and a layer (hereinafter also referred to as the "main layer" of the GaAs single-crystal substrate) located directly beneath the oxide layer and composed of gallium (Ga) and arsenic (As). The inventors found that if the area surrounding the interface has a composition richer in As₂O₅ than the other region of the oxide layer in the GaAs single-crystal substrate, the oxide layer is effectively removed by thermal cleaning. In other words, the inventors developed the concept of controlling the composition of the oxide layer in the area surrounding the interface to obtain a main surface with very good mirror-like properties.It should be noted that in the present description, the ‘surface’ of the oxide layer refers to a surface of the oxide layer opposite the GaAs single crystal substrate side. <Erstes integriertes Intensitätsverhältnis>

[0059] The GaAs single-crystal substrate according to the present embodiment has R1, R2, R3, R4, R5, and R6, each of which is the first integrated intensity ratio. The first integrated intensity ratio is obtained by determining the spectrum of the detection intensity of the 3d electron of arsenic with respect to the binding energy of the photoelectron emitted outwards from the gallium arsenide single-crystal substrate based on XPS, in which the X-rays are applied centrally to the main surface under each of the specific conditions described above (conditions 1 to 6). The first integrated intensity ratio is the ratio of the integrated intensity of the As element (As) 5+), which exists as As2O5, to the sum of the integrated intensity of the As element (As 5+ ), which exists as As2O5, the integrated intensity of the As element (As 3+ The integrated intensity of the As element (Ga-As), which exists as GaAs, and the integrated intensity of the As element (Metal-As), which exists as Metal-As, are used to calculate the values ​​of R1, R2, R3, R4, R5, R6, and R6. R1 is obtained by performing XPS under condition 1. R2 is obtained by performing XPS under condition 2. R3 is obtained by performing XPS under condition 3. R4 is obtained by performing XPS under condition 4. R5 is obtained by performing XPS under condition 5. R6 is obtained by performing XPS under condition 6.

[0060] If the first integrated intensity ratio is divided by R F The first integrated intensity ratio (R) is represented. F) can be represented by the following mathematical formula. RF=I(As2O5)I(As2O5)+I(As2O3)+I(GaAs)+I(As)

[0061] In the GaAs single-crystal substrate according to the present embodiment, a relationship is satisfied in which at least one of R2, R3, and R4 is the largest among R1, R2, R3, R4, R5, and R6. In particular, a relationship is preferably satisfied in which R1 is smaller than R2 and R3, respectively.

[0062] Fig.Figure 1 is an exemplary diagram showing a relationship between the depth of analysis (horizontal axis) from the main surface of the gallium arsenide single-crystal substrate according to the present embodiment and a ratio (vertical axis) of the integrated intensity of the arsenic element present as diarsene pentoxide, the integrated intensity of the arsenic element present as diarsene trioxide, and the integrated intensity of the arsenic element present as metal arsenic to the integrated intensity of the total arsenic elements. The triangles in Fig. The points marked in 1 correspond to R1, R2, R3, R4, R5 and R6, each representing the first integrated intensity ratio described above. From the diagram in Fig.It is evident from Figure 1 that R3, the first integrated intensity ratio obtained by performing the XPS under condition 3, is the largest among R1, R2, R3, R4, R5, and R6. Furthermore, it is evident that R1, the first integrated intensity ratio obtained by performing the XPS under condition 1, is smaller than R2 and R3.

[0063] Such a relationship means that the composition of the oxide layer near the interface between the oxide layer, located at a depth of approximately 1 to 2 nm from the main surface, and the main layer is richer in As₂O₅ than that of the rest of the oxide layer. In this case, it is assumed that the oxidation progress is suppressed over time until the oxide layer is thermally cleaned, allowing the oxide layer to be effectively removed by thermal cleaning.Therefore, if an epitaxial layer is grown on the main surface of the GaAs single-crystal substrate after thermal purification according to the present embodiment, both the maximum and mean values ​​of the haze of a surface of the epitaxial layer can be lower than in the conventional technique (for example, the maximum haze of the surface of the epitaxial layer can be less than or equal to 350 ppm and the mean haze can be less than or equal to 2.5 ppm). 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.

[0064] However, if R1, R2, R3, R4, R5, and R6, each representing the first integrated intensity ratio, are obtained by performing XPS on a conventional GaAs single-crystal substrate, the conventional GaAs single-crystal substrate does not satisfy the requirement that at least one of R2, R3, and R4 is the largest among R1, R2, R3, R4, R5, and R6, unlike the GaAs single-crystal substrate according to the present embodiment. For example, in a GaAs single-crystal substrate obtained by performing a liquid-phase process using a conventional acidic solution and / or an alkaline solution without performing the novel purification process described later, R1 is the largest value among R1 to R6, and part of the oxide layer may 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 large maximum and average haze values. It should be noted that R5 or R6 cannot, in reality, be the highest value from R1 to R6, as this would indicate a GaAs single-crystal substrate with a main surface on which no oxide layer or only a very thin oxide layer is present.

[0065] 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 As2O5 near the interface (area at a depth of 1 to 2 nm from the main surface) between the oxide layer and the main layer.

[0066] In the GaAs single-crystal substrate, R1, R2, R3, R4, R5, and R6 are preferably each greater than or equal to 0.05 and less than or equal to 0.55. If the proportion of As₂O₅ in the oxide layer is within the range described above, it is sufficiently low to allow for efficient decomposition by thermal purification. The values ​​of R1, R2, R3, R4, R5, and R6 are preferably greater than or equal to 0.1 and less than or equal to 0.5. It should be noted that a GaAs single-crystal substrate in which R1, R2, R3, R4, R5, and R6 are each less than 0.05 or greater than 0.55 is rare in practice.

[0067] Furthermore, R6 is preferably greater than or equal to 0.1 and less than or equal to 0.2. This indicates that the oxide layer is sufficiently thin to allow for more effective removal by thermal cleaning. R6 is preferably greater than or equal to 0.1 and less than or equal to 0.16.

[0068] R1 is preferably greater than or equal to 0.2 and less than 0.35. This indicates that the proportion of As2O5 in the top surface of the oxide layer is sufficiently low to allow for more effective removal of the oxide layer by thermal cleaning. R1 is even more preferably greater than or equal to 0.2 and less than or equal to 0.33. <durchmesser>

[0069] The GaAs single-crystal substrate preferably has a diameter greater than or equal to 75 mm and less than or equal to 205 mm. In other words, the diameter of the GaAs single-crystal substrate is preferably 3 to 8 inches. Thus, with the GaAs single-crystal substrate having a diameter greater than or equal to 75 mm and less than or equal to 205 mm, the main surface with good mirror surface properties can be obtained by effectively 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 (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 greater than or equal to 100 mm and less than or equal to 205 mm, and preferably has a diameter greater than or equal to 150 mm and less than or equal to 205 mm. <Verfahren zur Analyse eines GaAs-Einkristallsubstrats mittels Röntgen-Photoelektronenspektroskopie (XPS) unter Verwendung von Synchrotronstrahlung>

[0070] The following describes in more detail the method for analyzing the GaAs single crystal substrate using XPS with synchrotron radiation. (Analysis system)

[0071] Fig. Figure 2 is a schematic explanatory diagram illustrating the setup 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 generator 10, a vacuum chamber 20, and an electron spectrometer 30. The X-ray generator 10, the vacuum chamber 20, and the electron spectrometer 30 are coupled to each other in this order. The interior of the X-ray generator 10, the vacuum chamber 20, and the electron spectrometer 30 is maintained at an ultra-high vacuum. The pressure inside the X-ray generator 10, the vacuum chamber 20, and the electron spectrometer 30 is, for example, 4 × 10⁻⁶. -7 Pa.

[0072] The X-ray generating device 10 produces 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 generating device 10.

[0073] 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 the vacuum chamber 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 accordingly on the upstream and downstream sides with respect to the grating (spectrometer) 13. Each of the slots 12, 14 is, for example, a four-quadrant slot.

[0074] By deflecting the direction of motion of high-energy electrons by means of a magnetic field generated by a deflection electromagnet in a circular accelerator, the X-ray source 11 emits synchrotron radiation (X-rays) which is emitted in a direction tangential to the direction of motion.

[0075] 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.

[0076] 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.

[0077] 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 150 eV or 600 eV can be emitted from the X-ray source 10 by adjusting the emission angle in the grating using grating 13, where the slot width of each of slots 12 and 14 is 30 µm and the line density in the center is 400 L / mm.

[0078] 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.

[0079] 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.

[0080] An angle θ1 formed by the direction of incidence of the X-rays incident on the GaAs single-crystal substrate 1 from the X-ray source 10 and the main surface 1m 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 motion of the photoelectrons detected by the electron spectrometer 30 under the photoelectrons emitted by the GaAs single-crystal substrate 1 and its main surface 1m 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°.

[0081] For example, a high-resolution XPS analyzer “R3000” from Scienta Omicron can be used as an electron spectrometer 30. (Depth measured from the main area for analysis)

[0082] Some of the photoelectrons emitted from the GaAs single-crystal substrate 1 in response to X-ray irradiation 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. Therefore, the depth d (nm) from the main surface of the GaAs single-crystal substrate being analyzed is expressed by the following mathematical formula. In this formula, λ (nm) represents the IMFP value and θ2 represents the exit angle. d=3λ sin θ2

[0083] 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

[0084] In each of the mathematical formulas 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.

[0085] The depth d (nm) from 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) from 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 As element in As₂O₅ and As₂O₃, and the X-ray energy (150 eV or 600 eV). The depth d (nm) is as follows.

[0086] If the X-ray incident energy is 150 eV and the photoelectron exit angle is 30° (condition 1), the depth d is approximately 0.90 nm. If the X-ray incident energy is 150 eV and the photoelectron exit angle is 45° (condition 2), the depth d is approximately 1.28 nm. If the X-ray incident energy is 150 eV and the photoelectron exit angle is 85° (condition 3), the depth d is approximately 1.80 nm. If the X-ray incident energy is 600 eV and the photoelectron exit angle is 30° (condition 4), the depth d is approximately 2.25 nm. If the X-ray energy is 600 eV and the photoelectron exit angle is 45° (condition 5), the depth d is approximately 3.18 nm. If the X-ray energy With a voltage of 600 eV and a photoelectron exit angle of 85° (condition 6), the depth d is approximately 4.48 nm. (Method for calculating the first integrated intensity ratio (R1, R2, R3, R4, R5 and R6))

[0087] The following describes a method for calculating the first integrated intensity ratio (R1, R2, R3, R4, R5, and R6) in the main surface based on the XPS described above. In the present embodiment, XPS is first performed centrally on the main surface of the GaAs single-crystal substrate using X-rays with an energy of 150 eV or 600 eV. This yields the kinetic energy distribution of the photoelectrons emitted by the GaAs single-crystal substrate.

[0088] 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 a work function φ (eV). E=hv−EB−φ.

[0089] From the kinetic energy distribution of the photoelectrons emitted by the GaAs single-crystal substrate, a spectrum is generated using the mathematical formula above, which indicates the binding energy distribution of the electrons. In the present embodiment, an As-3d spectrum is generated, which indicates the binding energy distribution of the electrons based on the kinetic energy distribution of the photoelectrons emitted from the position at depth d (nm) relative to the main surface of the GaAs single-crystal substrate. In this description, "As-3d spectrum" refers to a spectrum representing the detection intensity of each photoelectron emitted from the 3d orbital of the As element (As₂O₅, As₂O₃, metal As, and the As contained in GaAs).

[0090] In XPS analysis, the As-3d spectrum is obtained by narrow sampling within a predetermined binding energy range to ensure precise measurement. Specifically, by narrow sampling within a binding energy range of 39 to 49 eV, the As-3d spectrum can be plotted in a graph, with the horizontal axis representing the range and the vertical axis representing the detection intensity.

[0091] The 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.

[0092] Fig. Figure 3 is a diagram showing an exemplary background-corrected As-3d spectrum obtained by X-ray photoelectron spectroscopy, in which X-rays are directed onto the main surface of the gallium arsenide single-crystal substrate according to the present embodiment. As shown in Fig. As shown in 3, the As element present as GaAs (i.e., the As element bonded to Ga: Ga-As) and the As element present as As2O5 (As) appear in the As-3d spectrum L. 5+ ), the As element present as As2O3 (As 3+ ) and the arsenic element present as metal arsenic (metal arsenic). The metal arsenic is formed from the oxide layer and the main layer through a reaction of 2 GaAs + As₂O₃ → Ga₂O₃ + 4 As.

[0093] Here, the background correction for the As-3d spectrum L is performed using the Shirley method (reference document: Kazuhiro Yoshihara: Journal of the Vacuum Society of Japan, 2013, Vol. 56, No. 6, pp. 243 to 247). Thus, the difference between the As-3d spectrum obtained from the actual measurement and the background can be determined as the As-3d spectrum L after background correction.

[0094] When determining the As-3d spectrum L, the peak of the detection intensity of As is also taken into account. 5+ set to a position corresponding to a binding energy of 45.57 eV, and the peak position of the detection intensity of As 3+ The peak of the detection intensity for metal As is set to a position corresponding to a binding energy of 44.07 eV. Furthermore, the peak of the detection intensity for metal As is set to a position corresponding to a binding energy of approximately 41.62 to 42.12 eV, giving it a broad range, and the peak of the detection intensity for GaAs is set to a position corresponding to a binding energy of approximately 40.77 to 41.27 eV, giving it a broad range. This is because when X-ray photoelectron spectroscopy is performed on the GaAs single crystal, a charge shift can occur, causing the As 3d spectrum L to be shifted by a maximum of approximately 1 eV towards higher energy. Furthermore, since each peak of the metal As and the Ga As is influenced by the main layer consisting of GaAs, and it is difficult to define the peak to a specific value, the peak position is set to a width of 0.5 eV as described above.

[0095] Next, the As-3d spectrum L, after background correction as described above, is expressed by decomposing the As-3d spectrum L into the following four Gaussian functions Y1, Y2, Y3, and Y4 (hereafter referred to as "peak separation"). In this way, the four spectra of the element As (Ga-As), which exists as GaAs, of the element As (As) can be expressed. 5+ ), which exists as As2O5, of the element As (As 3+ ), which exists as As2O3, and of the element As (metal As), which exists as metal As, are obtained by peak separation in the range of binding energy from 39 to 49 eV. Y1=a1*exp{(−(X−b1)2) / c12} Y2=a2*exp{(−(X−b2)2) / c22} Y3=a3*exp{(−(X−b3)2) / c32} Y4=a4*exp{(−(X−b4)2) / c42}

[0096] Of the four Gaussian functions, Y1 represents the spectrum of As 5+ , Y2 the spectrum of As 3+ Y3 is the spectrum of metallic As and Y4 the spectrum of Ga-As. The unit of each Gaussian function Y1, Y2, Y3 and Y4 is dimensionless, the unit of each X, b1, b2, b3, b4, c1, c2, c3 and c4 in the Gaussian functions Y1, Y2, Y3 and Y4 is eV, and the unit of each a1, a2, a3 and a4 is dimensionless.

[0097] The Gaussian functions Y1 to Y4 are optimized by optimizing each of the variables (a1, a2, a3, a4, b1, b2, b3, b4, c1, c2, c3, c4) such that the square ([actual measured value - ΣGi] 2 ) a deviation from the actual measured value becomes minimal, provided that the i-th component of the As-3d 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 detection intensities of As 5+ , As 3+ , Metal As and Ga-As, as described above, are each used in b1 to b4.

[0098] That is, each of the variables (a1, a2, a3, a4, b1, b2, b3, b4, c1, c2, c3, c4) is as follows.

[0099] a1, a2, a3 and a4 are each real numbers greater than or equal to 0, b1=45.57 eV b2=44.07 eV 41.62 eV≤b3≤42.12 eV 40.77 eV≤b4≤41.27 eV 0.2 eV ≤ c1 ≤ 0.95 eV 0.2 eV ≤ c² ≤ 0.95 eV 0.2 eV≤c3≤0.95 eV 0.2 eV≤c4≤1.2 eV.

[0100] Thus, the Gaussian functions Y1, Y2, Y3 and Y4 can each be considered as 5+ -Spectrum L1, As 3+ -Spectrum L2, metal-As spectrum L3 and Ga-As spectrum L4 are represented, which are obtained, for example, by peak separation from the As-3d spectrum L in Fig. 3 will be received.

[0101] It should be noted that the following correction can be made to determine the peak positions of the Gaussian functions Y1, Y2, Y3, and Y4. 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 other factors. Therefore, the data published on the following website are used as the value for η. Specifically, the photoionization efficiency (η) of X-rays with an incident energy of 150 eV is 6.63, and the photoionization efficiency (η) of X-rays with an incident energy of 600 eV is 0.42. https: / / vuo.elettra.eu / services / elements / WebElements.html (see data for 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)).

[0102] Furthermore, since the intensity of the X-ray radiation used in the synchrotron radiation facility decreases over time, an attenuation ratio of the Au4f photoelectron intensity is determined by measuring a gold (Au) standard sample at regular intervals and the dose of the X-ray radiation used is corrected on the basis of this ratio.

[0103] In Fig. 3 corresponds, for example, to a range between the Gaussian function Y1 (As 5+ -spectrum L1) 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 range between Y2 (As 3+ -Spectrum L2) 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 Y3 (metal-As spectrum L3) and the horizontal axis (X-axis) corresponds to the number of photoelectrons emitted from the 3d orbital of As and therefore represents the integrated intensity of the metal-As. A region between Y4 (Ga-As spectrum L4) and the horizontal axis (X-axis) corresponds to the number of photoelectrons emitted from the 3d orbital of Ga-As and therefore represents the integrated intensity of Ga-As. Therefore, the ratio of the integrated intensity of As can be determined. 5+ to the sum of the integrated intensity of As 5+ , the integrated intensity of As 3+ The integrated intensity of Ga-As and the integrated intensity of metal-As are determined based on the areas obtained from the Gaussian functions Y1, Y2, Y3, and Y4 described above and the horizontal axis, thus determining the first integrated intensity ratio. It should be noted that R1, R2, R3, R4, R5, and R6, each representing the first integrated intensity ratio, are determined when the XPS is performed under one of the corresponding conditions 1 to 6 described above. <Gleichmäßigkeit der Hauptoberfläche des GaAs-Einkristallsubstrats>

[0104] 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 on the main surface. The following embodiments (a first embodiment and a second embodiment) can be described as examples of such a preferred GaAs single-crystal substrate. (First embodiment)

[0105] The GaAs single-crystal substrate according to the first embodiment has a diameter greater than or equal to 75 mm and less than 150 mm. The GaAs single-crystal substrate preferably has a diameter greater than or equal to 75 mm and less than or equal to 105 mm. The GaAs single-crystal substrate has RS1, RS2, RS3, RS4, RS5, and RS6, each of which is a second integrated intensity ratio. The GaAs single-crystal substrate has a standard deviation and a mean value for each of RS1, RS2, RS3, RS4, RS5, and RS6.The standard deviation and mean value for RS1, RS2, RS3, RS4, RS5 and RS6 are obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a 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 irradiated onto the five measurement points on the main surface under each of the conditions 1, 2, 3, 4, 5 and 6.The standard deviation and mean of RS1, RS2, RS3, RS4, RS5 and RS6 are a standard deviation and mean of the ratio of the integrated intensity of the As element present as As2O5 to the sum of the integrated intensity of the As element present as As2O5, the integrated intensity of the As element present as As2O3, the integrated intensity of the As element present as GaAs and the integrated intensity of the As element present as metal As.

[0106] The ratio of the standard deviation of RS1 to the mean of RS1 is 0.1 or less. The ratio of the standard deviation of RS2 to the mean of RS2 is 0.1 or less. The ratio of the standard deviation of RS3 to the mean of RS3 is 0.1 or less. The ratio of the standard deviation of RS4 to the mean of RS4 is 0.2 or less. The ratio of the standard deviation of RS5 to the mean of RS5 is 0.2 or less. The ratio of the standard deviation of RS6 to the mean of RS6 is 0.11 or less.

[0107] If the diameter is denoted as 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 unit for D and for X and Y in the coordinates (X, Y) is mm. Since the oxide layer is thus effectively removed by thermal purification in the gallium arsenide single-crystal substrate with a diameter greater than or equal to 75 mm and less than 150 mm, it is possible to obtain a main surface with good mirror surface properties, allowing an epitaxial layer with a reduced turbidity value to form on it.

[0108] In particular, the GaAs single-crystal substrate according to the first embodiment preferably satisfies the following relationship: The ratio of the standard deviation of RS1 to the mean of RS1 is preferably 0.055 or less. The ratio of the standard deviation of RS2 to the mean of RS2 is preferably 0.093 or less. The ratio of the standard deviation of RS3 to the mean of RS3 is preferably 0.05 or less. The ratio of the standard deviation of RS4 to the mean of RS4 is 0.111 or less. The ratio of the standard deviation of RS5 to the mean of RS5 is preferably 0.113 or less. The ratio of the standard deviation of RS6 to the mean of RS6 is preferably 0.102 or less. For RS1, RS2, RS3, RS4, RS5, and RS6 respectively, the lower limit of the ratio of the standard deviation to the mean is 0, which is an ideal value.For example, the ratio of the standard deviation to the mean can be 0.026 or more for RS1, RS2, RS3, RS4, RS5 and RS6. (Second embodiment)

[0109] Furthermore, according to the second embodiment, a GaAs single-crystal substrate has a diameter greater than or equal to 150 mm and less than or equal to 205 mm. The GaAs single-crystal substrate has RT1, RT2, RT3, RT4, RT5, and RT6, each of which is a third integrated intensity ratio. The GaAs single-crystal substrate has a standard deviation and a mean value for each of these RT1, RT2, RT3, RT4, RT5, and RT6. The standard deviation and mean for RT1, RT2, RT3, RT4, RT5 and RT6 are obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a binding energy of a photoelectron emitted outwards from the GaAs single crystal substrate on the basis of an X-ray photoelectron spectroscopy in which X-ray radiation is irradiated onto each of five measurement points on the main surface under a corresponding condition from conditions 1, 2, 3, 4, 5 and 6.The standard deviation and mean of RT1, RT2, RT3, RT4, RT5 and RT6 are a standard deviation and mean of the ratio of the integrated intensity of the As element present as As2O5 to the sum of the integrated intensity of the As element present as As2O5, the integrated intensity of the As element present as As2O3, the integrated intensity of the As element present as GaAs and the integrated intensity of the As element present as metal As.

[0110] The ratio of the standard deviation of RT1 to the mean of RT1 is 0.1 or less. The ratio of the standard deviation of RT2 to the mean of RT2 is 0.1 or less. The ratio of the standard deviation of RT3 to the mean of RT3 is 0.2 or less. The ratio of the standard deviation of RT4 to the mean of RT4 is 0.2 or less. The ratio of the standard deviation of RT5 to the mean of RT5 is 0.1 or less. The ratio of the standard deviation of RT6 to the mean of RT6 is 0.2 or less.

[0111] If the diameter is denoted as D, and two axes, each passing through the center of the main surface, lying on the main surface and 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 unit of D, and of X and Y in the coordinates (X, Y), is mm. By effectively removing the oxide layer by thermal cleaning on the GaAs single crystal substrate with a diameter greater than or equal to 150 mm and less than or equal to 205 mm, a main surface with good mirror surface properties can be obtained, allowing an epitaxial layer with a reduced turbidity value to be formed on it.

[0112] In particular, the GaAs single-crystal substrate according to the second embodiment preferably fulfills the following relationship: The ratio of the standard deviation of RT1 to the mean of RT1 is preferably 0.071 or less. The ratio of the standard deviation of RT2 to the mean of RT2 is preferably 0.07 or less. The ratio of the standard deviation of RT3 to the mean of RT3 is preferably 0.11 or less. The ratio of the standard deviation of RT4 to the mean of RT4 is preferably 0.12 or less. The ratio of the standard deviation of RT5 to the mean of RT5 is preferably 0.092 or less. The ratio of the standard deviation of RT6 to the mean of RT6 is preferably 0.11 or less. For RT1, RT2, RT3, RT4, RT5, and RT6 respectively, the lower limit of the ratio of the standard deviation to the mean is 0, which is an ideal value.For example, the ratio of the standard deviation to the mean can be 0.039 or more for RT1, RT2, RT3, RT4, RT5 and RT6.

[0113] In the first and second embodiments described above, since conditions 1, 2, 3, 4, 5, and 6, which are the conditions for performing the XPS, correspond to the conditions 1, 2, 3, 4, 5, and 6 described above, which are the conditions for the XPS performed to determine the first integrated intensity ratio, the same explanation is not repeated. Furthermore, a specific analytical procedure for determining the second and third integrated intensity ratios is also the same as the procedure described in the section "Method for Analyzing a GaAs Single Crystal Substrate by X-ray Photoelectron Spectroscopy (XPS) Using Synchrotron Radiation," therefore the same explanation is not repeated. (Five measuring points and nine measuring points)

[0114] The GaAs single-crystal substrate according to the first embodiment has a diameter greater than or equal to 75 mm and less than 150 mm. In this case, the five measurement points are defined 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 the second integrated intensity ratio in the plane, it is suitable to define the five measurement points so that the distances between them are as large as possible, to determine the second integrated intensity ratio at each of the five measurement points, and to evaluate its deviation. Therefore, five circular measurement targets, each with a diameter of 20 mm, are first defined on the main surface of the GaAs single-crystal substrate so that the distances between them are as large as possible.Next, the center point of each measurement target is defined as the measurement point. Then, X-rays are directed onto the measurement point.

[0115] If the two axes, each passing through the center of the main surface, lie on the main surface and are orthogonal to each other, and are defined 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.

[0116] Among the five measurement points, the second, third, fourth, and fifth measurement points are arranged at equal intervals on 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 unit of D, as well as of X and Y in the coordinates (X, Y), is mm.

[0117] The GaAs single-crystal substrate according to the second embodiment has a diameter greater than or equal to 150 mm and less than or equal to 205 mm. In this case, four additional measuring points are added to the main surface of the GaAs single-crystal substrate according to the second embodiment, in addition to the five measuring points defined in the GaAs single-crystal substrate according to the first embodiment, resulting in a total of nine measuring points as follows.That is, on the main surface of the GaAs single-crystal substrate according to the second embodiment, in addition to the second, third, fourth, and fifth measurement points described above, four measurement targets, each with a diameter of 20 mm, are positioned such that they are located on the outer circumference with respect to these measurement points and do not overlap with the measurement targets, including the second, third, fourth, and fifth measurement points. The center point of each of the measurement targets is defined as a measurement point, and the measurement point is irradiated with X-rays. 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 unit of D and of X and Y in the coordinates (X, Y) is mm.

[0118] It is known that in a main surface with a large diameter of ≥ 150 mm and ≤ 205 mm, 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 at the outer periphery. 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 third integrated intensity ratio in the plane, it is appropriate to determine the third integrated intensity ratio in the region at the outer periphery in addition to the five measurement points described above, and thereby evaluate its variation.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 peripheral side so that the distances between them are as large as possible.

[0119] Fig. Figure 4 is an explanatory diagram showing the five measurement points defined in the gallium arsenide single crystal substrate with a diameter greater than or equal to 75 mm and less than 150 mm in the present embodiment. Fig. Figure 5 is an explanatory illustration showing the nine measuring points defined in the gallium arsenide single crystal substrate with a diameter greater than or equal to 150 mm and less than or equal to 205 mm in the present embodiment.

[0120] 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), which corresponds to the center of the GaAs single-crystal substrate, and a measurement target A1 is defined, which is a circular area with a diameter of 20 mm and has the first measurement point P1 as its center.

[0121] 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. Furthermore, a measurement target A2, a measurement target A3, a measurement target A4, and a measurement target A5 are defined, each a circular area with a diameter of 20 mm, centered accordingly around the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5.

[0122] 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.

[0123] As in Fig. Figure 5 shows that, in addition to the first measuring point P1 to the fifth measuring point P5, a sixth measuring point P6, a seventh measuring point P7, an eighth measuring point P8 and a ninth measuring point P9 are defined in the GaAs single crystal substrate according to the second embodiment. These four measuring points are defined at equal intervals on the circumference, which is located on the outer edge region 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 is offset inwards by 10 mm from the outer edge 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 accordingly 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.

[0124] If, for example, the in Fig. In the example shown, where the GaAs single-crystal substrate has a diameter of 150 mm, 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>

[0125] The GaAs single-crystal substrate preferably has an epitaxial layer arranged on its main surface. In this case, the maximum haze value of a surface of the epitaxial layer is preferably less than or equal to 350 ppm, and the average haze value of the surface of the epitaxial layer is preferably less than or equal to 2.5 ppm. The maximum haze value of the surface of the epitaxial layer is preferably less than or equal to 100 ppm, and the average haze value of the surface of the epitaxial layer is preferably less than or equal to 2.0 ppm. The lower limit of the maximum and average haze values ​​of the surface of the epitaxial layer is 0, which is an ideal value.

[0126] The epitaxial layer, for example, is a composite layer made of Al 1-y-z Ga y In z As consists of, where y can be greater than or equal to 0 and less than or equal to 1, z can be greater than or equal to 0 and less than or equal to 1, and the sum of y and z can be greater than or equal to 0 and less than or equal to 1. 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).

[0127] The epitaxial layer is formed, for example, with a thickness of 0.5 to 10 µm. If the thickness of the epitaxial layer is within the aforementioned range, the epitaxial substrate can be used in a wide range of applications. Preferably, the epitaxial layer has a thickness of 1 to 5 µm.

[0128] 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 contamination testing device (for example, the "Surfscan 6420" from KLA-Tencor Corporation). The device can perform measurements across the entire surface of the epitaxial layer (except for a 2 mm inward margin from the outer edge of the substrate) and determine the turbidity value (scattered light intensity (ppm)) per cm². 2 Measure on the surface of the epitaxial layer. Based on the result of such a measurement, the maximum and mean values ​​of the turbidity of the surface of the epitaxial layer can be determined. [Method for the preparation of a gallium arsenide single crystal substrate]

[0129] A method for producing a gallium arsenide single-crystal substrate (GaAs single-crystal substrate) according to the present embodiment is preferably a manufacturing process for producing the GaAs single-crystal substrate described above. The manufacturing process comprises, for example: a step (preparation step) for preparing a gallium arsenide single-crystal substrate precursor (hereinafter also referred to as "GaAs single-crystal substrate precursor") with a surface,which has a circular shape; and a purification step to obtain the GaAs single-crystal substrate from the GaAs single-crystal substrate precursor. The purification step comprises: a step (surface polishing step) to form the surface of the GaAs single-crystal substrate precursor to a polished surface by polishing the surface; a step (alkaline cleaning step) to form the polished surface to an alkaline-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid; a step (first acid cleaning step) to form the alkaline-cleaned surface to a first acid-cleaned surface by cleaning the alkaline-cleaned surface with an acid cleaning fluid containing 0.The process contains 3 wt. ppm or more and 1 wt.% or less of a first acid; a step (second acid cleaning step) to form the first acid-cleaned surface into a second acid-cleaned surface by immersing the first acid-cleaned surface in more than 0.5 wt.% and 1 wt.% or less of a second acid for 1 minute or longer; and a step (heat treatment step) to form the second acid-cleaned surface into a main surface by performing a heat treatment on the second acid-cleaned surface in an inert gas atmosphere under conditions of 100 °C or higher and 200 °C or lower for 1 minute or longer and 30 minutes or less. The second acid contains hydrofluoric acid and / or hydrochloric acid and / or nitric acid and / or nitrous acid. With this manufacturing process, it is possible toThe aim is to obtain a gallium arsenide 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. This makes it possible to obtain the gallium arsenide single-crystal substrate with a main surface on which the epitaxial layer has formed and exhibits a reduced turbidity value.

[0130] In the present description, the term ‘gallium arsenide single crystal substrate precursor (GaAs single crystal substrate precursor)’ means a GaAs single crystal substrate having a surface with a circular shape and cut from a gallium arsenide single crystal (hereinafter also referred to as ‘GaAs single crystal’) produced by a conventionally known manufacturing process such as the vertical boat process, and in particular a GaAs single crystal substrate to be subjected to each step included in the purification step.

[0131] The inventors focused their attention on modifying a conventionally known purification step for obtaining a 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. This alkaline cleaning agent adheres to the surface of the GaAs single-crystal substrate precursor after the acid purification step. Therefore, care is taken to perform a process after the acid purification step to enrich the oxide layer near the interface between the oxide layer and the GaAs layer contained within the GaAs single-crystal substrate with a composition rich in As₂O₅.In particular, further acid cleaning of the surface after the acid cleaning step described above causes the progression of the GaAs oxidation reaction to deposition an oxide layer on the surface, containing As₂O₃ as the main component. Subsequently, the surface was subjected to heat treatment. It was found that a redox reaction takes place between the As₂O₃ and the GaAs near the interface, the As sublimates, and As₂O₅ is formed secondarily, resulting in an As₂O₅-rich environment around the interface. In such a GaAs single-crystal substrate, the progression of oxide layer oxidation is suppressed over time, and the oxide layer can therefore be effectively removed by thermal cleaning.In this way, the inventors were able to obtain a GaAs single-crystal substrate with a main surface having good mirror surface properties and thus arrived at a method for producing a GaAs single-crystal substrate on which an epitaxial layer with a reduced turbidity value can be formed.

[0132] 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 preparing the gallium arsenide single crystal substrate according to the present embodiment. <Vorbereitungsschritt S100>

[0133] The process for preparing the GaAs single-crystal substrate includes the step (preparation step S100) of preparing the GaAs single-crystal substrate precursor with the circular surface. In preparation step S100, the GaAs single-crystal substrate precursor required for the purification step is prepared or manufactured. Preparation step S100 may include a step in which a conventionally known method for manufacturing a GaAs single-crystal substrate precursor is carried out. That is, preparation step S100 may include a step for manufacturing a gallium arsenide single crystal (hereinafter also referred to as the "GaAs single crystal") using a conventionally known manufacturing process, 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.The preparation step S100 can also include a step for processing 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 6 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>

[0134] The process for producing the GaAs single-crystal substrate includes 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 layer that can be effectively removed by thermal purification. Purification step S200 comprises: the step (surface polishing step S210) of shaping the surface of the GaAs single-crystal substrate precursor into a polished surface by polishing the surface; the step (alkaline purification step S220) of shaping the polished surface into an alkaline-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid; the step (first acid purification step S230) of shaping the surface into an alkaline-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid.Forming the alkaline-cleaned surface into a first acid-cleaned surface by cleaning the alkaline-cleaned surface with an acid cleaning fluid containing 0.3 ppm by mass or more and 1 percent by mass or less of a first acid; the step (second acid cleaning step S240) of forming or developing the first acid-cleaned surface into a second acid-cleaned surface by immersing the first acid-cleaned surface in a second acid containing more than 0.5 percent by mass and 1 percent by mass or less for 1 minute or longer; and the step (heat treatment step S250) of forming or developing 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 at 100 °C or higher and 200 °C or lower for 1 minute or longer and 30 minutes or less.The following section describes in detail each of the steps included in cleaning step S200. (Surface polishing step S210)

[0135] 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, such as conventional mechanical polishing and chemical-mechanical polishing. (Alkaline cleaning step S220)

[0136] The 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. This step removes foreign matter, impurities, or the like that adhere to the polished surface of the GaAs single-crystal substrate precursor. The alkaline cleaning fluid is not particularly restricted, but preferably an aqueous solution containing 0.1 to 10% by weight of an organic alkali compound that does not contain any metallic element that affects the electrical properties is used. Examples of such organic alkali compounds include a quaternary ammonium hydroxide such as choline or tetramethylammonium hydroxide (TMAH), a quaternary pyridinium hydroxide, or the like. (First acid cleaning step S230)

[0137] The first acid cleaning step, S230, is the step in which the alkaline-cleaned surface is formed by cleaning it with the acid cleaning fluid containing 0.3 ppm or more by mass and 1% or less by mass of the first acid. This first acid cleaning step, S230, removes impurities contained in the alkaline cleaning fluid and adhering to the alkaline-cleaned surface of the GaAs single-crystal substrate precursor through an oxidation reaction (etching of the alkaline-cleaned surface) with the acid cleaning fluid. Specifically, in the first acid cleaning step, S230, the alkaline-cleaned surface is cleaned with the acid cleaning fluid containing 0.3 ppm or more by mass and 1% or less by mass of the first acid.This ensures that the ratio of Ga atoms to As atoms on the main surface is appropriate and suppresses the formation of an excess oxide layer, allowing the oxide layer to be efficiently removed by thermal cleaning. In the first acid cleaning step S230, the alkaline-cleaned surface is preferably cleaned with an acid cleaning fluid containing 0.3 ppm by mass or more and 0.5 percent by mass or less of the first acid.

[0138] If the acid concentration of the first acid in the acid cleaning solution is less than 0.3 ppm by mass, its modifying effect on the alkaline-cleaned surface is minimal. However, the influence of carbon dioxide (CO2) gas dissolved from the ambient air into the acid cleaning solution becomes significant, altering the chemical composition of the surface cleaned with the first acid after the first acid cleaning step S230. If the acid concentration of the first acid in the acid cleaning solution exceeds 1% by mass, the deviation of the surface cleaned with the first acid from stoichiometry is substantial due to the effect of the first acid immediately after the first acid cleaning step S230. In this case, the chemical composition of the first acid-cleaned surface is richer in As than in Ga.However, the chemical composition of the first acid-cleaned surface is reversed due to the presence of carbon dioxide gas or similar substances in the atmosphere during subsequent drying or transport, becoming richer in gallium (Ga). Consequently, the chemical composition of the first acid-cleaned surface (and the main surface in the subsequent step) tends to change. Here, the term "stoichiometry" means that, given a particular compound, the ratio (composition) of the number of atoms that make up the compound is the same as in its chemical formula.

[0139] The first acid contained in the acid cleaning fluid is not particularly restricted, but is preferably an acid component that has high cleaning power, does not contain any element (for example, a metallic element, sulfur, or the like) that affects the electrical properties, and is less likely to cause serious secondary contamination and impairment of the equipment when the acid component evaporates together with a water component during droplet spraying in the equipment. For example, the first acid preferably contains an inorganic acid in the form of hydrofluoric acid (HF) and / or hydrochloric acid (HCl) and / or nitric acid (HNO3) and / or nitrous acid (HNO2). An organic acid such as acetic acid, citric acid, or malic acid may also preferably be used as the first acid.Furthermore, two or more of these acids can be used in combination; for example, hydrochloric acid and nitric acid can be used in combination.

[0140] From a cleaning performance standpoint, the acid cleaning fluid 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 acid cleaning fluid 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 first acid-cleaned surface.

[0141] In the first acid cleaning step S230, the acid cleaning fluid can be applied to the alkaline-cleaned surface while the GaAs single-crystal substrate precursor is rotated at 100 rpm or more and 800 rpm or less, keeping its surface horizontal. This allows a film of the acid cleaning fluid to form on the alkaline-cleaned surface, thus performing efficient acid cleaning while suppressing excessive oxidation. If the rotational speed of the GaAs single-crystal substrate precursor is less than 100 rpm, the cleaning efficiency may not be improved, while at a speed of more than 800 rpm, the acid cleaning fluid film may not form, and the oxidation suppression effect may be reduced.

[0142] Furthermore, after the first acid cleaning step S230, preferably immediately after the first acid cleaning step S230, the first 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 first 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. This suppresses the progression of excessive oxidation of the first acid-cleaned surface. 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 pure water purification process can also be carried out by supplying the pure water to the first acid-cleaned surface while the GaAs single-crystal substrate precursor is rotated at 100 rpm or more and 800 rpm or less, with its main surface held horizontally. (Second acid cleaning step S240)

[0143] The second acid cleaning step, S240, is a step in which the first acid-cleaned surface is transformed into a second acid-cleaned surface by immersing the first surface in a second acid concentration of more than 0.5% by mass and 1% by mass or less for 1 minute or longer. This second acid cleaning step, S240, allows the oxidation reaction of the GaAs in the first acid-cleaned surface to proceed further, enabling the deposition of an oxide layer containing As₂O₃ as its main component. Thus, in the subsequently described heat treatment step, S250, an oxidation-reduction reaction occurs between the As₂O₃ and the GaAs near the interface between the oxide layer and the layer composed of GaAs in the GaAs single-crystal substrate precursor, generating As₂O₅ near the interface.

[0144] In particular, during the second acid cleaning step S240, the first acid-cleaned surface is immersed in the second acid, with a concentration of more than 0.5% by mass and 1% by mass or less, for at least one minute. This allows the oxidation reaction of the GaAs on the first acid-cleaned surface to continue, thus preserving the second acid-cleaned surface where the oxide layer has formed. If the acid concentration of the second acid in the acid cleaning solution is 0.5% by mass or less, the modifying (oxidizing) effect on the first acid-cleaned surface is minimal.However, if the acid concentration of the second acid in the acid cleaning solution exceeds 1% by mass, the oxidation reaction of the GaAs on the first acid-cleaned surface proceeds excessively, which can make it difficult to remove the entire oxide layer by thermal cleaning. In the second acid cleaning step S240, the first acid-cleaned surface is preferably immersed further in the second acid, which has a composition of 0.7% by mass or less and 1% by mass or less, for 1 minute or longer.

[0145] In the second acid cleaning step S240, the immersion time of the first acid-cleaned surface in the second acid, as described above, is 1 minute or longer, preferably 1 minute or longer and 30 minutes or less, and even more preferably 1 minute or longer and 5 minutes or less. If the immersion time is less than 1 minute, the modifying (oxidizing) effect on the first acid-cleaned surface will be minimal. If the immersion time is more than 30 minutes, the disadvantage of increasing the time spent in cleaning step S200 may outweigh the advantage of the modifying effect on the first acid-cleaned surface.

[0146] The second acid contains an acid in the form of hydrofluoric acid and / or hydrochloric acid and / or nitric acid and / or nitrous acid. Each of these acids is advantageous because it has high cleaning power, contains no element (e.g., a metallic element, sulfur, or the like) that impairs electrical properties, and is less likely to cause serious secondary contamination and impairment of the system when the acid component evaporates along with a water component and droplets are scattered throughout the system. In addition to the acids described above, the second acid can also be used in conjunction with organic acids such as acetic acid, citric acid, and malic acid. Two or more of the acids described above can also be used in combination as the second acid. For example, hydrochloric acid and nitric acid can also be used in combination as the second acid.

[0147] 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. This suppresses the progression of excessive oxidation of the second acid-cleaned surface. For further suppression of excessive oxidation, the dissolved oxygen concentration of the pure water is preferably 50 ppb or less.The total organic carbon (TOC) content of the pure water is preferably 40 ppb or less to ensure low contamination. The pure water purification process 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 speeds of 100 rpm or more and 800 rpm or less, with its main surface held horizontally. (Heat treatment step S250)

[0148] The S250 heat treatment step is a step in which the second acid-cleaned surface is shaped into the main surface by heat treatment in an inert gas atmosphere at 100 °C or higher and 200 °C or lower for 1 minute or more and 30 minutes or less. The S250 heat treatment step can generate As₂O₅ by inducing an oxidation-reduction reaction between the As₂O₃ and the GaAs near the interface between the oxide layer, which contains as its main component the As₂O₃ segregated in the second acid-cleaned surface, and the layer composed of the GaAs in the GaAs single-crystal substrate precursor. In this way, a GaAs single-crystal substrate can be obtained with a main surface exhibiting an oxide layer with a high As₂O₅ content near the interface.Since the temporal progression of the oxidation of the oxide layer in the GaAs single crystal substrate is suppressed, the oxide layer can be effectively removed by thermal cleaning.

[0149] In heat treatment step S250, the heat treatment of the second acid-cleaned surface is carried out in an inert gas atmosphere at 100 °C or higher and 200 °C or lower for 1 minute or more and 30 minutes or less. The type of inert gas is not particularly restricted, but argon or nitrogen are preferable. The temperature for the heat treatment is preferably 125 to 175 °C. The duration of the heat treatment is preferably 10 to 20 minutes. By carrying out the heat treatment under the conditions described above, As₂O₅ can be suitably generated near the interface between the oxide layer and the GaAs-composite layer. If the temperature for the heat treatment is below 125 °C or the duration of the heat treatment is less than 1 minute, it tends to be difficult to generate sufficient quantities of As₂O₅ near the interface.If the temperature for heat treatment exceeds 175 °C or the duration of the heat treatment is more than 30 minutes, the GaAs single crystal substrate may be affected by excessive heating. <Schichtbildungsschritt S300> (Thermal cleaning step S310)

[0150] As described above, in the process for producing the GaAs single-crystal substrate according to the present embodiment, the GaAs single-crystal substrate can be obtained with the main surface containing the As₂O₅-enriched oxide layer near the interface between the oxide layer and the GaAs-composed main layer. The GaAs single-crystal substrate is preferably subjected to a thermal cleaning step S310 and an epitaxial layer formation step S320, which are described below as layer formation step S300. Even if the thermal cleaning of the GaAs single-crystal substrate is carried out under conventionally known conditions (for example, conditions of heat treatment at 550 °C for 5 minutes) in thermal cleaning step S310, the progression of oxide layer oxidation over time is suppressed, so that the oxide layer can be effectively removed. <Epitaxieschicht-Bildungsschritt S320>

[0151] The method for producing the GaAs single-crystal substrate according to the present embodiment preferably comprises the step (epitaxic layer formation step S320) of forming an epitaxial layer on the main surface, as described above. The epitaxial layer formation step S320 allows the GaAs single-crystal substrate to be obtained with a main surface on which an epitaxial layer with a reduced haze value is formed. For example, a maximum haze value of a surface of the epitaxial layer can be 350 ppm or less, and an average haze value of the surface can be 2.5 ppm or less, thereby achieving improved component properties.

[0152] A conventionally known method can be used to form the epitaxial layer on the main surface of the GaAs single-crystal substrate in epitaxial layer formation step S320. The properties of the epitaxial layer obtained in this step are the same as those described above in the section "Epitaxial Layer," therefore the same explanation is not repeated. Since the gallium arsenide single-crystal substrate, on whose main surface the epitaxial layer is formed, has a sufficiently low turbidity value, the gallium arsenide single-crystal substrate can be used for devices such as field-effect transistors, microwave diodes, other integrated circuits, and the like. Examples

[0153] The present revelation will be described in more detail below using examples, but the present revelation is not limited to these. [First test]

[0154] GaAs single-crystal substrates of samples 1 to 7 described below are examples of the present disclosure, and GaAs single-crystal substrates of samples 11 to 13 are comparative examples. <Herstellung eines GaAs-Einkristallsubstrats> (Sample 1)1) Preparation step

[0155] 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. 2) Surface polishing step

[0156] One surface of each GaAs single-crystal substrate precursor was subjected to conventional mechanical polishing and chemical-mechanical polishing. Thus, the GaAs single-crystal substrate precursor was produced with a polished surface having an arithmetic mean roughness Ra of 0.3 nm or less according to JIS B0601:2001 and with an offset angle of 2° to the (100) plane. 3) Alkaline cleaning

[0157] The polished surface of the GaAs single-crystal substrate precursor was immersed in an aqueous solution containing 0.5 wt% tetramethylammonium hydroxide for 10 minutes at room temperature (25 °C) using a vertical batch process. The GaAs single-crystal substrate precursor was then rinsed for 3 minutes with ultrapure water (electrical resistivity 18 MΩ·cm or greater, TOC less than 10 µg / L, and fine particle count less than 100 particles / L; the same applies to the subsequent description). 4) First acid cleaning step

[0158] The alkaline-cleaned surface of the GaAs single-crystal substrate precursor was acid-cleaned using a vertical batch process with an acid cleaning solution containing a first acid. For the acid cleaning, the alkaline-cleaned surface of the GaAs single-crystal substrate precursor was immersed at room temperature (25 °C) for 2 minutes in an aqueous hydrochloric acid solution containing 0.3 wt ppm hydrochloric acid as the first acid. The GaAs single-crystal substrate precursor was then rinsed for 3 minutes with the same ultrapure water used in the alkaline cleaning. This process converted the alkaline-cleaned surface to a first-acid-cleaned surface. 5) Second acid cleaning step

[0159] The first acid-cleaned surface of the GaAs single-crystal substrate precursor was subjected to acid cleaning according to the vertical batch process using an acid cleaning solution with a second acid. Specifically, the first acid-cleaned surface of the GaAs single-crystal substrate precursor was immersed for 10 minutes in an aqueous hydrochloric acid solution containing 0.6 wt% hydrochloric acid as the second acid. Subsequently, the GaAs single-crystal substrate precursor was rinsed for 3 minutes with the same ultrapure water used in the alkaline cleaning step. In this way, the first acid-cleaned surface became a second acid-cleaned surface. 6) Heat treatment step

[0160] The second acid-cleaned surface of the GaAs single-crystal substrate precursor was subjected to heat treatment for 30 minutes at 100 °C under an argon gas atmosphere. This process transformed the second acid-cleaned surface into a primary surface with a predetermined oxide layer. In this way, the required number of GaAs single-crystal substrates for 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. 7) Epitaxial layer formation step

[0161] The GaAs single-crystal substrate underwent thermal cleaning at 550 °C for 5 minutes. Furthermore, an aluminum oxide coating was applied. 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, each of which had undergone thermal purification, using a metal-organic vapor-phase epitaxy (MOVPE) process (hereinafter, the GaAs single-crystal substrate on whose main surface the epitaxial layer was grown is also 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. (Sample 2)

[0162] A required number of GaAs single-crystal substrates of sample 2 were obtained in the same manner as in sample 1, except that in the second acid purification step, the first acid-purified surface of the GaAs single-crystal substrate precursor was immersed for 5 minutes in an aqueous hydrochloric acid solution containing 0.8 wt% hydrochloric acid as the second acid, and in the heat treatment step, the second acid-purified surface of the GaAs single-crystal substrate precursor was subjected to heat treatment for 20 minutes in an argon gas atmosphere at 130 °C. 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, thereby obtaining an epitaxial substrate of sample 2. (Sample 3)

[0163] The required number of GaAs single-crystal substrates of sample 3 were obtained in the same manner as in sample 2, except that in the heat treatment step, the second acid-cleaned surface of the GaAs single-crystal substrate precursor was subjected to heat treatment in an argon gas atmosphere at 160 °C for 10 minutes. 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, thereby obtaining an epitaxial substrate of sample 3. (Sample 4)

[0164] A required number of GaAs single-crystal substrates of sample 4 were obtained in the same manner as in sample 1, except that in the second acid purification step, the first acid-purified surface of the GaAs single-crystal substrate precursor was immersed for 5 minutes in an aqueous hydrochloric acid solution containing 0.8 wt% hydrochloric acid as the second acid, and in the heat treatment step, the second acid-purified surface of the GaAs single-crystal substrate precursor was subjected to heat treatment in an argon gas atmosphere at 100 °C for 30 minutes. 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, thereby obtaining an epitaxial substrate of sample 4. (Sample 5)

[0165] The required number of GaAs single-crystal substrates of sample 5 were obtained in the same manner as in sample 1, except that in the heat treatment step, the second acid-cleaned surface of the GaAs single-crystal substrate precursor was subjected to heat treatment in an argon gas atmosphere at 150 °C for 15 minutes. 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, thereby obtaining an epitaxial substrate of sample 5. (Sample 6)

[0166] A required number of GaAs single-crystal substrates of sample 6 were obtained in the same manner as in sample 1, except that in the heat treatment step, the second acid-cleaned surface of the GaAs single-crystal substrate precursor was subjected to heat treatment in an argon gas atmosphere at 100 °C for 10 minutes. 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, resulting in an epitaxial substrate of sample 6. (Sample 11)

[0167] The required number of GaAs single-crystal substrates of sample 11 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, thereby obtaining an epitaxial substrate of sample 11. <Maximalwert und Mittelwert der Trübung der Oberfläche des Epitaxieschichts>

[0168] For the surface of the epitaxial layer in each of the epitaxial substrates of samples 1 to 6 and sample 11, a maximum and a mean turbidity value of the surface of the epitaxial layer in each sample were determined using a surface contaminant analysis device (trade name: "Surfscan 6420" by KLA-Tencor Corporation). The results are shown in Table 1.

[0169] Furthermore, based on the maximum and mean values ​​of the surface turbidity of the epitaxial layer, the quality of the epitaxial substrate of samples 1 to 6 and sample 11 was determined according to the following criteria. The results are shown in Table 1. 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. <Analyse von GaAs-Einkristallsubstraten mittels Röntgen-Photoelektronenspektroskopie>

[0170] X-rays with energies of 150 eV and 600 eV were generated using "BL17," one of the beamlines exclusively available to Sumitomo Electric Industries at SAGA Light Source. The X-rays were directed centrally onto the main surface of each of the GaAs single-crystal substrates of samples 1 to 6 and sample 11, enabling analysis by X-ray photoelectron spectroscopy. It should be noted that each of the GaAs single-crystal substrates of samples 1 to 6 and sample 11 could not be fully placed on a sample stage; therefore, a test piece was cut from each of the GaAs single-crystal substrates of samples 1 to 6 and sample 11, and the analysis was performed on this test piece.

[0171] The analysis conditions are as follows. Condition 1: X-ray incidence energy of 150 eV and photoelectron exit angle of 30° Condition 2: X-ray incidence energy of 150 eV and photoelectron exit angle of 45°. Condition 3: X-ray incidence energy of 150 eV and photoelectron exit angle of 85°. Condition 4: X-ray incidence energy of 600 eV and photoelectron exit angle of 30°. Condition 5: X-ray incidence energy of 600 eV and photoelectron exit angle of 45°. Condition 6: X-ray incidence energy of 600 eV and photoelectron exit angle of 85°.

[0172] Size of the test piece under each condition: 10 mm × 10 mm

[0173] Pressure in the area of ​​the test piece for each condition: 4×10 -7 Pa

[0174] Use of the high-resolution XPS analyzer (trade name: "R3000" from Scienta Omicron) for each condition Energy resolution E / ΔE: 3480 Plot interval for binding energy: 0.02 eV Integration time and number of integrations for each energy value: 100 ms and 50,

[0175] Based on the As-3d spectra obtained by the analyses under the above-mentioned conditions (conditions 1 to 6), R1, R2, R3, R4, R5 and R6 were determined, where each is the first integrated intensity ratio, the first integrated intensity ratio being the ratio of the integrated intensity of the As element (As) 5+ ), which exists as As2O5, to the sum of the integrated intensity of the As element (As 5+ ), which exists as As2O5, the integrated intensity of the As element (As 3+ The integrated intensity of the As element (Ga-As), which exists as GaAs, and the integrated intensity of the As element (Metal-As), which exists as Metal-As, are shown in Table 1. In addition to the first integrated intensity ratios R1, R2, R3, R4, R5, and R6, Table 1 also shows the ratio of the integrated intensity of As. 5+ to the sum of the integrated intensity of As 3+ , the integrated intensity of Ga-As and the integrated intensity of metal-As shown. [Table 1] Table 1 Sample number Type of arsenic 150eV 600eV Turbidity (ppm) Determination 30° 45° 85° 30° 45° 85° Max Medium 1 As 5+ 0,33(R1) 0,38(R2) 0,51(R3) 0,30(R4) 0,15(R5) 0,10(R6) 311 2.3 B As 3+ 0,64 0,57 0,38 0,41 0,31 0,25 Metal Ace 0,01 0,01 0,02 0,04 0,10 0,07 2 As 5+ 0,30(R1) 0,33(R2) 0,41(R3) 0,18(R4) 0,16(R5) 0,16(R6) 14 1.05 A As 3+ 0,60 0,54 0,41 0,46 0,37 0,24 Metal Ace 0,02 0,02 0,04 0,07 0,10 0,09 3 As 5+ 0,32(R1) 0,36(R2) 0,43(R3) 0,20(R4) 0,10(R5) 0,10(R6) 23 1.1 A As 3+ 0,65 0,56 0,43 0,40 0,32 0,26 Metal Ace 0,01 0,01 0,02 0,04 0,10 0,07 4 As 5+ 0,28(R1) 0,36(R2) 0,35(R3) 0,23(R4) 0,11(R5) 0,09(R6) 231 1.7 B As 3+ 0,61 0,45 0,41 0,38 0,36 0,30 Metal Ace 0,01 0,02 0,03 0,07 0,07 0,05 5 As 5+ 0,21(R1) 0,28(R2) 0,30(R3) 0,31(R4) 0,15(R5) 0,12(R6) 145 1.8 B As 3+ 0,73 0,58 0,50 0,38 0,32 0,28 Metal Ace 0,01 0,02 0,03 0,07 0,07 0,05 6 As 5+ 0,15(R1) 0,17(R2) 0,25(R3) 0,20(R4) 0,14(R5) 0,11(R6) 285 2 B As 3+ 0,77 0,69 0,54 0,47 0,31 0,27 Metal Ace 0,01 0,02 0,03 0,07 0,07 0,05 11 As 5+ 0,43(R1) 0,43(R1) 0,38(R3) 0,23(R4) 0,19(R5) 0,17(R6) >10000 393 C As 3+ 0,49 0,45 0,44 0,41 0,34 0,23 Metal Ace 0,02 0,02 0,03 0,09 0,10 0,10 <bewertung>

[0176] According to Table 1 above, the quality of each of the epitaxial substrates of samples 1 to 6, which each satisfy the relationship that at least one of the values ​​R2, R3, and R4 is the largest among R1, R2, R3, R4, R5, and R6 with respect to the first integrated intensity ratios R1, R2, R3, R4, R5, and R6, was determined to be C. Conversely, the quality of the epitaxial substrate of sample 11, which did not satisfy the above relationship, was determined to be C. It should be noted that a GaAs single-crystal substrate in which R5 or R6 is the largest among the first integrated intensity ratios R1 to R6 is an example where there is no oxide layer or a very thin oxide layer on the main surface, which is not realistic and is therefore not shown as a sample. [Second test]

[0177] Each of the GaAs single crystal substrates of samples 21 to 24 described below is an example of the present disclosure. <Herstellung eines GaAs-Einkristallsubstrats>(Sample 21)1) Preparation step

[0178] A GaAs single-crystal substrate precursor with a diameter of 3 inches (76.5 mm) and a thickness of 350 µm was prepared by cutting and beveling 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. 2) Surface polishing step

[0179] One surface of each of the GaAs single-crystal substrate precursors was subjected to conventional mechanical polishing and chemical-mechanical polishing. In this way, a GaAs single-crystal substrate precursor with a polished surface with an arithmetic mean roughness Ra of 0.3 nm or less according to JIS B0601:2001 and with an offset angle of 2° with respect to the (100) plane was produced. 3) Alkaline cleaning

[0180] The polished surface of the GaAs single-crystal substrate precursor was immersed in an aqueous solution containing 0.5 wt% tetramethylammonium hydroxide for 10 minutes at room temperature (25 °C) using a vertical batch process. The GaAs single-crystal substrate precursor was then rinsed for 3 minutes with ultrapure water (electrical resistivity 18 MΩ·cm or greater, TOC less than 10 µg / L, and fine particle count less than 100 particles / L; the same applies to the following description). 4) First acid cleaning step

[0181] The alkaline-cleaned surface of the GaAs single-crystal substrate precursor was acid-cleaned using a vertical batch or stacking process with an acid cleaning solution containing a first acid. For the acid cleaning, the alkaline-cleaned surface of the GaAs single-crystal substrate precursor was immersed at room temperature (25 °C) for 2 minutes in an aqueous hydrochloric acid solution containing 0.3 wt ppm hydrochloric acid as the first acid. Subsequently, the GaAs single-crystal substrate precursor was rinsed for 3 minutes with the same ultrapure water used in the alkaline cleaning. This process converted the alkaline-cleaned surface to a first-acid-cleaned surface. 5) Second acid cleaning step

[0182] The first acid-cleaned surface of the GaAs single-crystal substrate precursor underwent acid cleaning according to the vertical batch process using an acid cleaning solution containing a second acid. Specifically, the first acid-cleaned surface of the GaAs single-crystal substrate precursor was immersed for 5 minutes in an aqueous hydrochloric acid solution containing 0.8% by mass as the second acid. Subsequently, the GaAs single-crystal substrate precursor was rinsed for 3 minutes with the same ultrapure water used in the alkaline cleaning step. Thus, the first acid-cleaned surface became a second acid-cleaned surface. 6) Heat treatment step

[0183] The second acid-cleaned surface of the GaAs single-crystal substrate precursor was subjected to heat treatment for 20 minutes under an argon gas atmosphere at 130 °C. This transformed the second acid-cleaned surface into a primary surface with a predetermined oxide layer. In this way, a GaAs single-crystal substrate of sample 21 was obtained. The diameter and thickness of the GaAs single-crystal substrate precursor were retained in the GaAs single-crystal substrate. (Sample 22)

[0184] A GaAs single crystal substrate of sample 22 was obtained in the same way as in sample 21, except that in the fabrication 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 in (100 mm) and a thickness of 350 µm. (Sample 23)

[0185] A GaAs single crystal substrate of sample 23 was obtained in the same way as in sample 21, 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 in (150 mm) and a thickness of 675 µm. (Sample 24)

[0186] A GaAs single crystal substrate of sample 24 was obtained in the same way as in sample 21, 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 in. (200 mm) and a thickness of 675 µm. <Analyse der Gleichmäßigkeit der Hauptoberfläche des GaAs-Einkristallsubstrats> (Samples 21 and 22)

[0187] Five test pieces cut from each of the main surfaces of the GaAs single-crystal substrates of samples 21 and 22 were analyzed in the same manner as in [Analysis of the GaAs single-crystal substrate by X-ray photoelectron spectroscopy] in the first test. Thus, the ratio of the integrated intensity (second integrated intensity ratio) of the integrated intensity of the metal As to the sum of the integrated intensity of As was determined. 5+ , the integrated intensity of As 3+ The integrated intensity of Ga-As and the integrated intensity of the metal-As in each test piece were determined. Additionally, the standard deviation and mean of the second integrated intensity ratio were calculated based on the ratio, thus yielding a standard deviation / mean value.

[0188] Each of the five test pieces has 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 located in Fig. Figure 4 shows the results. Furthermore, each of the five test pieces was placed in a high-resolution XPS analyzer to illuminate X-rays at the first measurement point P1, the second measurement point P2, the third measurement point P3, the fourth measurement point P4, and the fifth measurement point P5. The results are shown in Tables 2 and 3. Table 2 shows the second integrated intensity ratio in the GaAs single-crystal substrate of sample 21, along with its standard deviation and mean. Table 3 shows the second integrated intensity ratio in the GaAs single-crystal substrate of sample 22, along with its standard deviation and mean. The smaller the standard deviation / mean value in Tables 2 and 3, the more uniform the properties of the GaAs single-crystal substrate are across the main surface. (Samples 23 and 24)

[0189] Nine test pieces, cut from each main surface of the GaAs single-crystal substrates of samples 23 and 24, 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 ratio of the integrated intensity (third integrated intensity ratio) of the integrated intensity of the metal As to the sum of the integrated intensity of As was determined. 5+ , the integrated intensity of As 3+ The integrated intensity of Ga-As and the integrated intensity of the metal-As in each test piece were determined. Additionally, the standard deviation and mean of the third integrated intensity ratio were calculated based on the ratio, thus yielding a standard deviation / mean value.

[0190] Each of the nine test pieces has a first measuring point P1, a second measuring point P2, a third measuring point P3, a fourth measuring point P4, a fifth measuring point P5, a sixth measuring point P6, a seventh measuring point P7, an eighth measuring point P8 and a ninth measuring point P9, which are located in Fig. The results are shown in Tables 5. Furthermore, each of the nine test pieces was placed in a high-resolution XPS analyzer to irradiate X-rays onto the first measurement point P1, the second measurement point P2, the third measurement point P3, the fourth measurement point P4, the fifth measurement point P5, the sixth measurement point P6, the seventh measurement point P7, the eighth measurement point P8, and the ninth measurement point P9. The results are shown in Tables 4 and 5. Table 4 shows the third integrated intensity ratio in the GaAs single-crystal substrate of sample 23, along with its standard deviation and mean. Table 5 shows the third integrated intensity ratio in the GaAs single-crystal substrate of sample 24, along with its standard deviation and mean. The smaller the standard deviation / mean value in Tables 4 and 5, the more uniform the property of the GaAs single-crystal substrate in the plane of the main surface. [Table 2] Table 2 Measuring point Coordinates(X,Y) Second integrated intensity ratio 150eV 600eV 30°(RS1) 45°(RS2) 85°(RS3) 30°(RS4) 45°(RS5) 85°(RS6) P1 (0,0) 0,31 0,34 0,40 0,20 0,17 0,15 P2 (19,125,0) 0,29 0,35 0,39 0,25 0,18 0,16 P3 (0,19,125) 0,29 0,32 0,38 0,19 0,17 0,16 P4 (-19,125,0) 0,30 0,35 0,40 0,23 0,20 0,15 P5 (0,-9,125) 0,29 0,31 0,38 0,23 0,17 0,16 Mean / Standard deviation σσ / Mean 0,30 0,33 0,39 0,22 0,18 0,16 0,009 0,018 0,010 0,024 0,013 0,005 0,030 0,054 0,026 0,111 0,073 0,035 [Table 3] Table 3 Measuring point Coordinates(X,Y) Second integrated intensity ratio 150eV 600eV 30°(RS1) 45°(RS2) 85°(RS3) 30°(RS4) 45°(RS5) 85°(RS6) P1 (0,0) 0,29 0,35 0,38 0,25 0,18 0,13 P2 (25,0) 0,27 0,32 0,4 0,3 0,21 0,14 P3 (0,25) 0,31 0,38 0,37 0,26 0,16 0,12 P4 (25,0) 0,28 0,3 0,35 0,28 0,21 0,14 P5 (0,25) 0,3 0,36 0,38 0,24 0,2 0,11 Mean / Standard deviation σσ / Mean 0,29 0,34 0,38 0,27 0,19 0,13 0,016 0,032 0,018 0,024 0,022 0,013 0,055 0,093 0,048 0,091 0,113 0,102 [Table 4] Table 4 Measuring point Coordinates(X,Y) Third integrated intensity ratio 150eV 600eV 30°(RT1) 45°(RT2) 85°(RT3) 30°(RT4) 45°(RT5) 85°(RT6) P1 (0,0) 0,33 0,32 0,37 0,27 0,18 0,17 P2 (37,5,0) 0,31 0,32 0,40 0,23 0,19 0,18 P3 (0,37,5) 0,32 0,34 0,40 0,24 0,20 0,19 P4 (-37,5,0) 0,30 0,35 0,37 0,21 0,19 0,19 P5 (0,-37,5) 0,32 0,36 0,36 0,20 0,17 0,17 P6 (65,0) 0,28 0,30 0,38 0,25 0,17 0,15 P7 (0,65) 0,29 0,31 0,28 0,24 0,15 0,16 P8 (-65,0) 0,27 0,31 0,39 0,23 0,19 0,19 P9 (0,-65) 0,28 0,32 0,36 0,27 0,16 0,16 Mean / Standard deviation σσ / Mean 0,30 0,33 0,37 0,24 0,18 0,17 0,021 0,020 0,036 0,024 0,016 0,015 0,071 0,062 0,099 0,100 0,092 0,087 [Table 5] Table 5 Measuring point Coordinates(X,Y) Third integrated intensity ratio 150eV 600eV 30°(RT1) 45°(RT2) 85°(RT3) 30°(RT4) 45°(RT5) 85°(RT6) P1 (0,0) 0,31 0,35 0,37 0,21 0,19 0,18 P2 (50,0) 0,30 0,32 0,37 0,23 0,18 0,16 P3 (0,50) 0,31 0,33 0,36 0,21 0,18 0,17 P4 (-50,0) 0,30 0,31 0,37 0,23 0,20 0,14 P5 (0,-50) 0,28 0,35 0,34 0,18 0,17 0,15 P6 (90,0) 0,32 0,33 0,39 0,24 0,21 0,15 P7 (0,90) 0,30 0,34 0,36 0,21 0,20 0,19 P8 (-90,0) 0,32 0,34 0,38 0,22 0,20 0,18 P9 (0,-90) 0,33 0,35 0,36 0,18 0,17 0,15 Mean / Standard deviation σσ / Mean 0,31 0,34 0,37 0,21 0,19 0,16 0,015 0,014 0,014 0,021 0,015 0,017 0,048 0,042 0,039 0,099 0,077 0,106 <bewertung>

[0191] According to Tables 2 and 3, in the GaAs single-crystal substrates of samples 21 and 22, the standard deviation and mean of the second integrated intensity ratio obtained by performing XPS under condition 1 (X-ray incident energy of 150 eV and photoelectron exit angle of 30°) satisfy a relationship in which the standard deviation / mean is ≤ 0.1. The standard deviation and mean of the second integrated intensity ratio obtained by performing XPS under condition 2 (X-ray incident energy of 150 eV and photoelectron exit angle of 45°) satisfy the relationship in which the standard deviation / mean is ≤ 0.1.The standard deviation and mean of the second integrated intensity ratio obtained by performing XPS under condition 3 (X-ray incident energy of 150 eV and photoelectron exit angle of 85°) satisfy the relationship where the standard deviation / mean is ≤ 0.1. The standard deviation and mean of the second integrated intensity ratio obtained by performing XPS under condition 4 (X-ray incident energy of 600 eV and photoelectron exit angle of 30°) satisfy the relationship where the standard deviation / mean is ≤ 0.2. The standard deviation and mean of the second integrated intensity ratio obtained by performing XPS under condition 5 (X-ray incident energy of 600 eV and photoelectron exit angle of 45°) satisfy the relationship in which the standard deviation / mean is ≤ 0.2.The standard deviation and mean of the second integrated intensity ratio obtained by performing XPS under condition 6 (X-ray incident energy of 600 eV and photoelectron exit angle of 85°) satisfy the relationship in which the standard deviation / mean ≤ 0.11.

[0192] According to Tables 4 and 5, in the GaAs single-crystal substrate of samples 23 and 24, the standard deviation and mean of the third integrated intensity ratio obtained by performing XPS under condition 1 (X-ray incident energy of 150 eV and photoelectron exit angle of 30°) satisfy the relationship in which the standard deviation / mean is ≤ 0.1. The standard deviation and mean of the third integrated intensity ratio obtained by performing XPS under condition 2 (X-ray incident energy of 150 eV and photoelectron exit angle of 45°) satisfy the relationship in which the standard deviation / mean is ≤ 0.1.The standard deviation and mean of the third integrated intensity ratio obtained by performing XPS under condition 3 (X-ray incident energy of 150 eV and photoelectron exit angle of 85°) satisfy the relationship that the standard deviation / mean is ≤ 0.2. The standard deviation and mean of the third integrated intensity ratio obtained by performing XPS under condition 4 (X-ray incident energy of 600 eV and photoelectron exit angle of 30°) satisfy the relationship that the standard deviation / mean is ≤ 0.2. The standard deviation and mean of the third integrated intensity ratio obtained by performing XPS under condition 5 (X-ray incident energy of 600 eV and photoelectron exit angle of 45°) satisfy the relationship that the standard deviation / mean is ≤ 0.1.The standard deviation and mean of the third integrated intensity ratio, obtained by performing XPS under condition 6 (X-ray incident energy of 600 eV and photoelectron exit angle of 85°), satisfy the relationship that the standard deviation / mean is ≤ 0.2. This indicates that the surface properties of the GaAs single-crystal substrate of each of samples 21 to 24 are sufficiently uniform in the plane of the main surface. Therefore, the GaAs single-crystal substrate of each of samples 21 to 24 exhibits good mirror surface properties across its entire main surface, and an epitaxial layer with a reduced haze value can be expected to form on it.

[0193] The embodiments and examples of the present disclosure have been explained above, but it can be assumed that the configurations of the embodiments and examples can be combined in a suitable manner.

[0194] The embodiments and examples disclosed herein are in every respect illustrative and non-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 include all modifications in scope and meaning that correspond to the terms of the claims. LIST OF REFERENCE MARKS

[0195] 1 GaAs single crystal substrate; 1 m main surface; 10 X-ray generating device; 11 X-ray source; 12, 14 slot; 13 grating; 20 vacuum chamber; 30 electron spectrometer; 50 notch; 100 analysis system; L As 3d spectrum; L1 As 5+ -Spectrum; L2 As 3+ -Spectrum; L3 Metal-As spectrum; L4 Ga-As 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 Alkaline cleaning step; S230 First acid cleaning step; S240 Second acid cleaning step; S250 Heat treatment step; S300 Epitaxial layer 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 06-045318

[0002] JP 2008-300747

[0002] Zitierte Nicht-Patentliteratur

[0000] Method of Estimating Inelastic Mean Free Path of Electrons by Tpp-2M Formula", Journal of Surface Analysis, Band 1, Nr. 2, 1995

[0083] Kazuhiro Yoshihara: Journal of the Vacuum Society of Japan, 2013, Vol. 56, Nr. 6, S. 243 bis 247

[0093] https: / / vuo.elettra.eu / services / elements / WebElements.html

[0101] J.J. Yeh, Atomic Calculation of Photoionization Cross-Sections and Asymmetry Parameters, Gordon and Breach Science Publishers, Langhorne, PE (USA), 1993 und J.J. Yeh und I. Lindau, Atomic Data and Nuclear Data Tables, 32, 1-155 (1985

[0101] < / bewertung> < / bewertung> < / epitaxieschicht> < / durchmesser>

Claims

[1] A gallium arsenide single crystal substrate having a main surface of circular shape, wherein the gallium arsenide single crystal substrate R1, R2, R3, R4, R5 and R6, each of which is a first integrated intensity ratio, the first integrated intensity ratio is obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a 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 onto the main surface centrally under a specific condition described below, the first integrated intensity ratio is a ratio of an integrated intensity of an arsenic element present as diarsene pentoxide to a sum of the integrated intensity of the arsenic element present as diarsene pentoxide, of an integrated intensity of an arsenic element present as diarsene trioxide, of an integrated intensity of an arsenic element present as gallium arsenide, and of an integrated intensity of an arsenic element present as metallarsene. R1 is obtained by performing X-ray photoelectron spectroscopy under a condition 1 described below, R2 is obtained by performing X-ray photoelectron spectroscopy under a condition 2 described below, R3 is obtained by performing X-ray photoelectron spectroscopy under a condition 3 described below, R4 is obtained by performing X-ray photoelectron spectroscopy under a condition 4 described below, R5 is obtained by performing X-ray photoelectron spectroscopy under a condition 5 described below, R6 was obtained by performing X-ray photoelectron spectroscopy under a condition 6 described below, and a relationship is satisfied whereby R2 and / or R3 and / or R4 is the largest among R1, R2, R3, R4, R5 and R6, where Condition 1: X-ray incidence energy of 150 eV and photoelectron exit angle of 30°, Condition 2: X-ray incidence energy of 150 eV and photoelectron exit angle of 45°, Condition 3: X-ray incidence energy of 150 eV and photoelectron exit angle of 85°, Condition 4: X-ray incidence energy of 600 eV and photoelectron exit angle of 30°, Condition 5: X-ray incidence energy of 600 eV and photoelectron exit angle of 45°, and Condition 6: X-ray incidence energy of 600 eV and photoelectron exit angle of 85°. [2] The gallium arsenide single crystal substrate according to claim 1, wherein R1, R2, R3, R4, R5 and R6 are each greater than or equal to 0.05 and less than or equal to 0.

55. [3] The gallium arsenide single crystal substrate according to claim 1 or 2, wherein R6 is greater than or equal to 0.1 and less than 0.

2. [4] The gallium arsenide single crystal substrate according to any one of claims 1 to 3, wherein R1 is greater than or equal to 0.2 and less than 0.

35. [5] The gallium arsenide single crystal substrate according to any one of claims 1 to 4, wherein the gallium arsenide single crystal substrate has a diameter greater than or equal to 75 mm and less than or equal to 205 mm. [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 greater than or equal to 75 mm and less than 150 mm, the gallium arsenide single crystal substrate RS1, RS2, RS3, RS4, RS5 and RS6, each of which is a second integrated intensity ratio, the gallium arsenide single crystal substrate has a standard deviation and a mean value for each RS1, RS2, RS3, RS4, RS5 and RS6, the standard deviation and the mean value for each RS1, RS2, RS3, RS4, RS5 and RS6 is obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a 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 irradiated onto each of five measurement points on the main surface under a corresponding condition 1, 2, 3, 4, 5 and 6, the standard deviation and mean of each RS1, RS2, RS3, RS4, RS5 and RS6, a standard deviation and mean of the ratio of the integrated intensity of the arsenic element present as diarsenic pentoxide to the sum of the integrated intensity of the arsenic element present as diarsenic pentoxide, the integrated intensity of the arsenic element present as arsenic trioxide, the integrated intensity of the arsenic element present as gallium arsenide, and the integrated intensity of the arsenic element present as metal arsenic, are the ratio of the standard deviation of RS1 to the mean of RS1 is less than or equal to 0.1, the ratio of the standard deviation of RS2 to the mean of RS2 is less than or equal to 0.1, the ratio of the standard deviation of RS3 to the mean of RS3 is less than or equal to 0.1, the ratio of the standard deviation of RS4 to the mean of RS4 is less than or equal to 0.2, the ratio of the standard deviation of RS5 to the mean of RS5 is less than or equal to 0.2, the ratio of the standard deviation of RS6 to the mean of RS6 is less than or equal to 0.11, and 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, 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 respectively in the coordinates (X, Y) are mm. [7] 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 greater than or equal to 150 mm and less than or equal to 205 mm, the gallium arsenide single crystal substrate has RT1, RT2, RT3, RT4, RT5 and RT6, each of which is a third integrated intensity ratio, the gallium arsenide single crystal substrate has a standard deviation and a mean value for each RT1, RT2, RT3, RT4, RT5 and RT6, the standard deviation and mean of each RT1, RT2, RT3, RT4, RT5 and RT6 is obtained by determining a spectrum of a detection intensity of a 3d electron of arsenic with respect to a 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 irradiated onto each of nine measurement points on the main surface under one of conditions 1, 2, 3, 4, 5 and 6, the standard deviation and mean of RT1, RT2, RT3, RT4, RT5 and RT6 are each a standard deviation and a mean of the ratio of the integrated intensity of the arsenic element present as diarsene pentoxide to the sum of the integrated intensity of the arsenic element present as diarsene pentoxide, the integrated intensity of the arsenic element present as arsenic trioxide, the integrated intensity of the arsenic element present as gallium arsenide, and the integrated intensity of the arsenic element present as arsenic metal. the ratio of the standard deviation of RT1 to the mean of RT1 is less than or equal to 0.1, the ratio of the standard deviation of RT2 to the mean of RT2 is less than or equal to 0.1, the ratio of the standard deviation of RT3 to the mean of RT3 is less than or equal to 0.2, the ratio of the standard deviation of RT4 to the mean of RT4 is less than or equal to 0.2, the ratio of the standard deviation of RT5 to the mean of RT5 is less than or equal to 0.1, the ratio of the standard deviation of RT6 to the mean of RT6 is less than or equal to 0.2, and 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, 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 / 2-10, 0), (0, D / 2-10), (-(D / 2-10), 0) and (0, -(D / 2-10)), and the units of D and X and Y, respectively, are in the coordinates (X, Y) mm. [8] The gallium arsenide single crystal substrate according to any one of claims 1 to 7, comprising an epitaxial layer arranged on the main surface, wherein a maximum turbidity value of a surface of the epitaxial layer is less than or equal to 350 ppm and a mean turbidity of the surface of the epitaxial layer is less than or equal to 2.5 ppm. [9] 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 Shaping the surface of the gallium arsenide single-crystal substrate precursor into a polished surface by polishing the surface, Transformation of the polished surface into an alkaline-cleaned surface by cleaning the polished surface with an alkaline cleaning fluid, Forming an alkaline-cleaned surface into a first acid-cleaned surface by cleaning the alkaline-cleaned surface with an acid cleaning fluid containing 0.3 ppm by mass or more and 1 percent by mass or less of a first acid, Forming the first acid-cleaned surfaces into a second acid-cleaned surface by immersing the first acid-cleaned surfaces in a second acid with more than 0.5% by mass and 1% by mass or less for 1 minute or longer, and Shaping the second acid-cleaned surface relative to the main surface by performing a heat treatment on the second acid-cleaned surface in an inert gas atmosphere at 100 °C or higher and 200 °C or lower for 1 minute or longer and 30 minutes or shorter, and wherein the second acid contains hydrofluoric acid and / or hydrochloric acid and / or nitric acid and / or nitrous acid. [10] The method for producing a gallium arsenide single crystal substrate according to claim 9 comprises forming an epitaxial layer on the main surface. [11] The gallium arsenide single crystal substrate according to claim 2, wherein R6 is greater than or equal to 0.1 and less than 0.2, R1 is greater than or equal to 0.2 and less than 0.35 and The gallium arsenide single crystal substrate has a diameter greater than or equal to 75 mm and less than or equal to 205 mm.

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