Gallium arsenide single crystal substrate, method for producing gallium arsenide single crystal, and method for producing gallium arsenide single crystal substrate

Abstract

The present application relates to a gallium arsenide single crystal substrate, a method for manufacturing a gallium arsenide single crystal, and a method for manufacturing a gallium arsenide single crystal substrate. The gallium arsenide single crystal substrate of the present application is of an electron-donating type. The gallium arsenide single crystal substrate has a main surface of a circular shape. The gallium arsenide single crystal substrate contains an electron-donating dopant. The value of the absorption coefficient of the gallium arsenide single crystal substrate at a wavelength of 1-μm infrared rays, which is measured after electron beam irradiation of the gallium arsenide single crystal substrate is performed under conditions where the acceleration voltage is 2 MeV and the irradiation dose is 150 kGy, is 95% or more and 100% or less of the value of the absorption coefficient of the gallium arsenide single crystal substrate at a wavelength of 1-μm infrared rays, which is measured before the electron beam irradiation is performed. The present application can provide a gallium arsenide single crystal substrate capable of reducing performance degradation caused by exposure to radiation and the like.

Description

Technical Field

[0001] This invention relates to gallium arsenide single crystal substrates, methods for manufacturing gallium arsenide single crystals, and methods for manufacturing gallium arsenide single crystal substrates. Background Technology

[0002] Japanese Patent Publication No. 2011-527280 (Patent Document 1) discloses a method for manufacturing a gallium arsenide single crystal substrate (hereinafter also referred to as "GaAs single crystal substrate") with a small light absorption coefficient in the near-infrared region. International Patent Publication No. 2012 / 160781 (Patent Document 2) discloses a GaAs single crystal substrate with high carrier concentration and high crystallinity. Japanese Patent Application Publication No. 2004-115339 (Patent Document 3) relates to the manufacture of gallium arsenide single crystals (hereinafter also referred to as "GaAs single crystals") with added silicon (Si) as an impurity using a vertical boat method, and discloses a method for manufacturing GaAs single crystals that prevents dislocations due to boron arsenide precipitation.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Publication No. 2011-527280;

[0006] Patent Document 2: International Publication No. 2012 / 160781;

[0007] Patent document 3: Japanese Patent Application Publication No. 2004-115339.

[0008] Non-patent literature

[0009] Non-patent literature 1: Nanotech Japan Bulletin Vol.13, No.1, 2020, pp.1-8;

[0010] Non-patent literature 2: Phys.ReV.B, Vol.52, No.15, (1995), 10932. Summary of the Invention

[0011] The problem the invention aims to solve

[0012] In the context of assuming the use of optical devices in a cosmic environment, it is possible to require reliability in maintaining stable operation under exposure to cosmic radiation. For example, Nanotech Japan Bulletin Vol. 13, No. 1, 2020, P1-8 (Non-Patent Document 1) evaluated the degradation of gallium nitride devices caused by a 2 MeV electron beam from a solar flare. In Phys. ReV. B, Vol. 52, No. 15, (1995), 10932 (Non-Patent Document 2), the introduction and recovery of point defects under irradiation with a 1.5 MeV electron beam were evaluated for Si-doped GaAs single-crystal substrates manufactured using the horizontal Bridgman process. However, from the viewpoint of reliability, a GaAs single-crystal substrate with excellent characteristics suitable for the aforementioned optical devices has not yet been realized. Therefore, it is desirable to develop a GaAs single-crystal substrate that meets the above requirements.

[0013] In view of the above-mentioned actual situation, the object of the present invention is to provide a GaAs single crystal substrate that can reduce performance degradation caused by exposure to radiation, etc., a method for manufacturing GaAs single crystal, and a method for manufacturing GaAs single crystal substrate.

[0014] Solution for solving the problem

[0015] The gallium arsenide single crystal substrate of the present invention is an electron-donating gallium arsenide single crystal substrate with a conductivity type of electron donation. The gallium arsenide single crystal substrate has a circular main surface. The gallium arsenide single crystal substrate contains an electron-donating dopant. The absorption coefficient of the gallium arsenide single crystal substrate at a wavelength of 1 micrometer, measured after electron beam irradiation of at least one side of the main surface at an accelerating voltage of 2 MeV and an irradiation dose of 150 kGy, is 95% or more and 100% or less of the absorption coefficient of the gallium arsenide single crystal substrate at a wavelength of 1 micrometer measured before electron beam irradiation.

[0016] Invention Effects

[0017] According to the present invention, a GaAs single crystal substrate capable of reducing performance degradation caused by exposure to radiation or the like, a method for manufacturing a GaAs single crystal, and a method for manufacturing a GaAs single crystal substrate are provided. Attached Figure Description

[0018] Figure 1 This is an explanatory diagram illustrating the GaAs single crystal substrate of this embodiment, and the measurement area (measurement region) used to measure the absorption coefficient of infrared light with a wavelength of 1 micrometer on the substrate.

[0019] Figure 2This is an explanatory diagram illustrating a Hall measurement sample made using the central portion of the aforementioned substrate for measuring the carrier concentration of the GaAs single-crystal substrate in this embodiment.

[0020] Figure 3 This is a flowchart illustrating a general method for manufacturing a GaAs single crystal and a GaAs single crystal substrate according to this embodiment.

[0021] Figure 4 The method for manufacturing GaAs single crystals according to this embodiment is illustrated by a diagram showing the process of growing GaAs single crystals using a single crystal growth apparatus. Detailed Implementation

[0022] [Description of Embodiments of the Invention]

[0023] First, a summary of the embodiments of the present invention will be given. Through repeated and in-depth research, the inventors have realized the present invention, which solves the aforementioned problems. Specifically, the focus is on reducing the change in the activation rate of the n-type dopant before and after exposure to radiation in a GaAs single-crystal substrate with an electron-donating conductivity type (hereinafter also referred to as "n-type"). With this focus, the aforementioned GaAs single crystal is manufactured using a vertical boat method by controlling the amount of n-type dopant added and the arsenic (As) partial pressure in the crucible, etc., to make the activation rate of the n-type dopant in the GaAs single crystal approximately 50%. It was discovered that under these conditions, the change in the absorption coefficient of infrared light at a wavelength of 1 micrometer in the GaAs single-crystal substrate obtained from the aforementioned GaAs single crystal is small before and after electron beam irradiation under specified conditions. Therefore, a GaAs single-crystal substrate capable of reducing performance degradation due to exposure to radiation was conceived, and the present invention was completed.

[0024] The following description will illustrate embodiments of the present invention.

[0025] [1] One aspect of the GaAs single-crystal substrate of the present invention is an n-type GaAs single-crystal substrate. The GaAs single-crystal substrate has a circular main surface. The GaAs single-crystal substrate contains an n-type dopant. The absorption coefficient of the GaAs single-crystal substrate at a wavelength of 1 micrometer, measured after electron beam irradiation of at least one side of the main surface under the conditions of an accelerating voltage of 2 MeV and an irradiation dose of 150 kGy, is 95% or more and 100% or less of the absorption coefficient of the GaAs single-crystal substrate at a wavelength of 1 micrometer measured before electron beam irradiation. The GaAs single-crystal substrate having such characteristics can reduce performance degradation caused by exposure to radiation, etc. Therefore, the GaAs single-crystal substrate can be used as a substrate for optical devices intended for use in a space environment.

[0026] [2] [1] The GaAs single crystal substrate described above can have a density of 3.5 × 10⁻⁶. 18 cm -3 Above and 5.0×10 18 cm -3 The following carrier concentrations are used. The GaAs single-crystal substrate described above can have an activation rate of 40% or more and 60% or less for the aforementioned n-type dopant. In this case, GaAs single-crystal substrates with good yield can be provided, which can reduce performance degradation caused by exposure to radiation, etc.

[0027] [3] [2] The GaAs single crystal substrate described herein may have an activation rate of 45% or more and 55% or less of the aforementioned n-type dopant. In this case, a GaAs single crystal substrate with good yield can be provided, which can reduce performance degradation caused by exposure to radiation, etc.

[0028] [4] Any one of [1] to [3] may have a GaAs single crystal substrate with a density of 5.8 × 10⁻⁶. 18 cm -3 Above and 1.3×10 19 cm -3 The atomic concentrations of the above-mentioned n-type dopants are as follows. In this case, it is possible to prevent an excessive decrease in the activation rate of the n-type dopants.

[0029] [5] The GaAs single-crystal substrate described in any one of [1] to [4] may contain boron (B). The above-mentioned GaAs single-crystal substrate may have a 4.0 × 10⁻⁶ ohm diameter. 18 cm -3 Above and 6.0×10 18 cm -3 The atomic concentration of B mentioned above is as follows. In this case, GaAs single-crystal substrates with good yield can be provided, which can reduce performance degradation caused by exposure to radiation, etc.

[0030] [6] In any one of the GaAs single-crystal substrates described in [1] to [5], the absorption coefficient of the GaAs single-crystal substrate with a wavelength of 1 micrometer for infrared radiation, measured before electron beam irradiation, can be 3.6 cm⁻¹. -1 In this case, it is possible to provide a GaAs single-crystal substrate with excellent optical properties.

[0031] [7] In any one of the GaAs single-crystal substrates [1] to [6], the aforementioned n-type dopant may be at least one selected from silicon (Si), tellurium (Te), and tin (Sn). In this case, a GaAs single-crystal substrate with good yield can be provided that can reduce performance degradation caused by exposure to radiation, etc.

[0032] [8] Any one of the GaAs single crystal substrates described in [1] to [7] can have a 1000 cm⁻¹ -2 The following dislocation density allows for the provision of GaAs single-crystal substrates with excellent optical properties.

[0033] [9] [8] The GaAs single crystal substrate described above may contain at least Si as the aforementioned n-type dopant. The aforementioned GaAs single crystal substrate may have a 2.0 × 10⁻⁶ Ų·m³·s⁻¹ ... 18 cm -3 The above refers to the atomic concentration of Si. The above-mentioned GaAs single-crystal substrate can have a 100cm³ atomic concentration. -2 The following dislocation density allows for the provision of nGaAs single-crystal substrates with excellent optical properties.

[0034]

[10] One aspect of the present invention is a method for manufacturing GaAs single crystals of the n-type conductivity type using a vertical boat method. The manufacturing method described above includes the following steps: preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; accommodating a seed crystal formed from the GaAs single crystal at the bottom of the crucible, and accommodating an n-type dopant, boron oxide (B₂O₃), metallic arsenic, and a bulk GaAs polycrystal at a position higher than the seed crystal within the crucible; heating the crucible with the heating device to sublimate the metallic arsenic, while simultaneously melting the B₂O₃ into a B₂O₃ molten liquid, melting a portion of the seed crystal and the GaAs polycrystal into a GaAs molten liquid, and obtaining a first molten liquid containing the n-type dopant dissolved in the GaAs molten liquid, and contacting the first molten liquid with the remaining portion of the seed crystal; and growing a crystal from the first molten liquid on the remaining portion of the seed crystal, thereby obtaining the GaAs single crystal. The single crystal growth apparatus includes a branch section for controlling the arsenic partial pressure within the crucible. In the process of obtaining the GaAs single crystal described above, the end face of the first melt that does not contact the remaining portion of the seed crystal is covered by the B2O3 melt with an area percentage of 10% to 50% or less. In the process of obtaining the GaAs single crystal described above, the GaAs in the first melt has a stoichiometric ratio of As to gallium (Ga) exceeding 1. By employing a manufacturing method with these characteristics, GaAs single crystals whose performance degradation due to exposure to radiation, etc., is reduced can be obtained.

[0035]

[11]

[10] In the process of obtaining GaAs single crystal, the crucible may not be rotated and the first molten liquid may not be stirred. In this case, it is possible to obtain a GaAs single crystal with an activation rate of about 50% for the n-type dopant.

[0036]

[12] One aspect of the present invention is a method for manufacturing a GaAs single crystal substrate, which includes the following steps: processing the GaAs single crystal obtained by the manufacturing method of GaAs single crystal described in

[10] or

[11] to obtain a GaAs single crystal substrate having a circular main surface. By means of a manufacturing method with such features, by reducing performance degradation caused by exposure to radiation, etc., a GaAs single crystal substrate suitable as a substrate for optical devices intended for use in a space environment can be obtained.

[0037] [Details of the embodiments of the present invention]

[0038] The following describes one embodiment of the present invention (hereinafter also referred to as "this embodiment") in further detail, but the present invention is not limited thereto. The accompanying drawings are sometimes referred to in conjunction with the description. Figure 1 While providing explanations, elements that are identical or corresponding in this specification and the accompanying drawings will not be described repeatedly using the same symbols. Furthermore, in the accompanying drawings, the scale has been adjusted appropriately for easier understanding of each component; the scale of each component shown in the drawings may not be the same as the actual scale of the component.

[0039] In this specification, designations in the form of "A~B" refer to the upper and lower limits of a range (i.e., above A and below B). Where no unit is specified in A but only in B, the unit of A is the same as the unit of B. Furthermore, when compounds are represented by chemical formulas in this specification, unless specifically defined by atomic ratio, the aforementioned compounds include all conventionally known atomic ratios and should not be limited to stoichiometric ranges. For example, when designated as "GaAs," unless specifically stated otherwise, the ratio of the number of atoms constituting GaAs is not limited to Ga∶As=1∶1, but includes all conventionally known atomic ratios. This also applies to the designation of compounds other than "GaAs."

[0040] In this specification, the "main surface" of a GaAs single-crystal substrate refers to both of the two circular faces of the substrate. The GaAs single-crystal substrate falls within the scope of this invention if at least one of these two faces satisfies the claims of this invention. An epitaxial film is sometimes disposed on the "main surface" of the GaAs single-crystal substrate. Furthermore, in this specification, the term "face" used in the term "in-plane" means "main surface." Furthermore, when the diameter of the GaAs single-crystal substrate is described as "70 mm," it means a diameter of approximately 70 mm (to the extent of 70 to 76.5 mm), or 3 inches. When the diameter is described as "100 mm," it means a diameter of approximately 100 mm (to the extent of 95 to 105 mm), or 4 inches. When the diameter is described as "150 mm," it means a diameter of approximately 150 mm (to the extent of 145 to 155 mm), or 6 inches. When the diameter is specified as "210mm", it means that the diameter is approximately 210mm (around 195-210mm), or it means 8 inches. This diameter can be measured using conventionally known outside diameter measuring instruments such as vernier calipers.

[0041] In this specification, a "dislocation" is a type of crystal defect, referring to a defect in which atomic displacement occurs in a linear fashion within the crystal lattice (a line defect). When the aforementioned "dislocation" slips (deviates) in a certain region within the crystal, it can be identified as a dislocation line generated at the boundary between the slipped and non-slipped regions. Furthermore, the magnitude and direction of the slip accompanying the aforementioned "dislocation" are represented by the Burgers vector.

[0042] In this specification, "yield" means the proportion of the mass of the GaAs single crystal ingot formed from the GaAs single crystal grown in the crucible described above, which, when processed into a GaAs single crystal substrate, is the mass that can be evaluated as a qualified product. Furthermore, a higher "yield" (shown as a larger value) indicates that more GaAs single crystal substrates can be obtained from the GaAs single crystal grown in the crucible described above.

[0043] In the crystallographic descriptions in this specification, [] represents a single crystal direction, <> represents a family of crystal directions, () represents a single crystal plane, and {} represents a family of crystal planes. Furthermore, while negative crystallographic indices are typically expressed by a hyphen (-) above the number, in this specification, a minus sign is placed before the number.

[0044] [GaAs single crystal substrate]

[0045] The GaAs single-crystal substrate of this embodiment is an n-type GaAs single-crystal substrate. The GaAs single-crystal substrate has a circular main surface. The GaAs single-crystal substrate contains an n-type dopant. The absorption coefficient of the GaAs single-crystal substrate at a wavelength of 1 micrometer, measured after electron beam irradiation of at least one side of the main surface at an accelerating voltage of 2 MeV and an irradiation dose of 150 kGy, is 95% to 100% of the absorption coefficient of the GaAs single-crystal substrate at a wavelength of 1 micrometer measured before electron beam irradiation. Because the GaAs single-crystal substrate with this characteristic exhibits a small rate of change in infrared absorption coefficient before and after electron beam irradiation, it can reduce performance degradation caused by exposure to radiation, etc. Therefore, the GaAs single-crystal substrate can be used as a substrate for optical devices intended for use in a space environment.

[0046] In the GaAs single-crystal substrate of this embodiment, the performance degradation caused by exposure to radiation is reduced based on the following characteristics. Specifically, the performance degradation of single-crystal substrates made of materials such as compound semiconductor single crystals in the cosmic environment is usually caused by the knock-on of atoms generated when cosmic radiation irradiates the substrate, resulting in the destruction of the structure (e.g., crystal lattice structure) of the substrate material. Compound semiconductors are typically n-type or p-type depending on the occupancy of impurity elements called dopants in the crystal. However, when the knock-on of these atoms occurs due to radiation irradiation, the occupancy of the dopants in the crystal changes, sometimes adversely affecting various physical properties such as electrical characteristics. Therefore, if the change in the occupancy of the substrate before and after exposure to radiation can be reduced even when the substrate is exposed to radiation, it means that the degradation of the substrate caused by exposure to radiation can be reduced.

[0047] The GaAs single-crystal substrate of this embodiment sometimes has characteristic carrier concentrations and n-type dopant atomic concentrations, as described later. The aforementioned GaAs single-crystal substrate sometimes contains impurity elements other than n-type dopant, such as B, at a predetermined atomic concentration. Furthermore, as shown in the manufacturing method described later, the GaAs single crystal used in the aforementioned GaAs single-crystal substrate can be obtained by using a vertical boat method, where the upper part of the molten liquid in the crucible is partially coated with B2O3 while crystal growth is performed by controlling the As partial pressure within the crucible, etc. In this case, the activation rate of the n-type dopant in the GaAs single-crystal substrate obtained by processing the aforementioned GaAs single crystal can be approximately 50%.

[0048] If the activation rate of the n-type dopant in the aforementioned GaAs single-crystal substrate is approximately 50%, the change in activation rate caused by atomic ejection due to exposure to radiation in the aforementioned GaAs single-crystal substrate is smaller than the change in activation rate in a GaAs single-crystal substrate where the activation rate of the n-type dopant is close to 100%. For example, when the main surface of the aforementioned GaAs single-crystal substrate is irradiated with an electron beam at an accelerating voltage of 2 MeV and an irradiation dose of 150 kGy, the change rate of the absorption coefficient of infrared light at a wavelength of 1 micrometer before and after irradiation is as low as less than 5%. That is, the aforementioned GaAs single-crystal substrate with an n-type dopant activation rate close to 50% can reduce the degradation of the substrate caused by exposure to radiation, etc. In summary, the GaAs single-crystal substrate of this embodiment can reduce performance degradation caused by exposure to radiation, etc., and therefore can be used as a substrate for optical devices intended for use in a space environment.

[0049] <Main Surface>

[0050] Figure 1 This is an explanatory diagram illustrating the GaAs single-crystal substrate of this embodiment, and the measurement area (measurement region) used to measure the absorption coefficient of infrared light with a wavelength of 1 micrometer on the substrate. Figure 1 As shown, the GaAs single-crystal substrate 1 has a circular main surface 11. In this specification, the term "circular shape" to describe the shape of the main surface 11 includes not only a geometrically circular shape, but also a shape in which the main surface 11 does not form a geometrically circular shape because at least one of a notch, an orientation flat (hereinafter also referred to as "OF"), or an index flat (hereinafter also referred to as "IF") is formed on the outer periphery of the main surface 11. Here, "the shape in which the main surface does not form a geometrically circular shape" refers to a shape in which the length of the line segment extending from any point on the outer periphery of the main surface 11 to the center O of the main surface 11 is shorter than the length of the line segment extending from any point on the notch, OF, or IF to the center O of the main surface 11. Furthermore, "the shape in which the main surface does not form a geometrically circular shape" also includes a shape in which the length of all line segments extending from any point on the outer periphery of the main surface 11 to the center O of the main surface 11 is not necessarily the same due to the shape of the GaAs single crystal, which is the raw material of the GaAs single-crystal substrate 1. In this context, the center O of the main surface 11 refers to the location of the center of gravity. The diameter of the GaAs single crystal substrate 1 refers to the length of the longest line segment extending from any point on the outer periphery of the GaAs single crystal substrate 1 through the center O of the main surface 11 to other points on the outer periphery.

[0051] (Offset Angle)

[0052] The main surface 11 can be the {100} plane of a GaAs single crystal. For example, Figure 1 The main surface 11 of the GaAs single crystal substrate 1 shown can be the {100} plane. Furthermore, the main surface 11 of the GaAs single crystal substrate 1 can also be a plane with an offset angle greater than 0° and less than 15° from the {100} plane.

[0053] When the main surface 11 of the GaAs single crystal substrate 1 is a {100} plane, or when the main surface 11 has an offset angle greater than 0° and less than 15° from the {100} plane, the main surface 11 of the GaAs single crystal substrate 1 becomes an orientation surface with excellent electrical and optical properties. Therefore, in this embodiment, a GaAs single crystal substrate 1 can be provided with a main surface 11 that is easy to process into elements that are rectangular or square, formed by cleaving the {100} plane of GaAs. Thus, the GaAs single crystal substrate 1 can be suitable for optical devices. The GaAs single crystal substrate 1 can be a main surface 11 with a {100} plane, or a main surface 11 with an offset angle greater than 0° and less than 10° from the {100} plane. The GaAs single crystal substrate 1 can be a main surface 11 with a {100} plane, or a main surface 11 with an offset angle greater than 0° and less than 5° from the {100} plane.

[0054] <diameter>

[0055] The diameter of the GaAs single crystal substrate 1 can be 95 mm or more and 205 mm or less. Specifically, the diameter of the GaAs single crystal substrate 1 with a diameter of 95 mm or more and 205 mm or less can be 100 mm, 150 mm, or 200 mm; in other words, the diameter can be 4 inches, 6 inches, or 8 inches. Therefore, performance degradation caused by exposure to radiation can be reduced in large-diameter GaAs single crystal substrates 1 with a diameter of 95 mm or more and 205 mm or less. Furthermore, as mentioned above, the diameter of the GaAs single crystal substrate 1 can be measured using conventionally known outer diameter measuring instruments such as vernier calipers.

[0056] <Conductivity type is n-type>

[0057] As described above, the GaAs single-crystal substrate 1 exhibits an n-type conductivity type. The GaAs single-crystal substrate 1 contains n-type dopants. That is, the GaAs single-crystal substrate 1 exhibits an n-type conductivity type as described above by containing n-type dopants. When forming an optical device by stacking, for example, an epitaxial layer on the main surface 11, a light-emitting layer (active layer) can be directly formed on the GaAs single-crystal substrate 11. Since the conductivity type is n-type, an n-type cladding layer, a DFB (Distributed Feedback) layer, or a DBR (Distributed Bragg Reflector) layer can also be formed.

[0058] (n-type dopant)

[0059] The GaAs single-crystal substrate 1, as described above, contains an n-type dopant. This n-type dopant can be at least one selected from Si, Te, and Sn. When the n-type dopant in the GaAs single-crystal substrate 1 is, for example, Si, the Si can be introduced into both Ga sites where Ga might be present and As sites where As might be present in the GaAs lattice structure of the GaAs single-crystal substrate 1. Therefore, by adjusting the amount of Si present at Ga sites and the amount of Si present at As sites, the activation rate of the n-type dopant in the GaAs single-crystal substrate 1 can be controlled. The GaAs single-crystal substrate 1 can contain two elements such as Si and Te; Si and Sn; Te and Sn; or three elements such as Si, Te, and Sn.

[0060] (Atomic concentration of n-type dopant)

[0061] GaAs single crystal substrate 1 can have 5.8 × 10⁻⁶ ℃. 18 cm -3 Above and 1.3×10 19 cm -3 The atomic concentrations of the above-mentioned n-type dopants are as follows. GaAs single-crystal substrate 1 can have an atomic concentration of 6.0 × 10⁻⁶. 18 cm -3 Above and 1.15×10 19 cm -3 The atomic concentration of the above-mentioned n-type dopants can also be 7.0 × 10⁻⁶. 18 cm -3 Above and 1.0×10 19 cm -3The atomic concentrations of the aforementioned n-type dopants are as follows. When the atomic concentrations of the n-type dopants are within the aforementioned range, the GaAs single-crystal substrate 1 can prevent an excessive decrease in the activation rate of the n-type dopants. In the GaAs single-crystal substrate 1, when the activation rate of the n-type dopants decreases excessively, it is difficult to provide it as a substrate for forming high-quality optical devices. When the GaAs single-crystal substrate 1 contains two or more of the aforementioned n-type dopants, the aforementioned "atomic concentration of the n-type dopants" refers to the total atomic concentration of the two or more n-type dopants.

[0062] The types and atomic concentrations of n-type dopants contained in the GaAs single-crystal substrate 1 can be determined using glow discharge mass spectrometry (GDMS). GDMS refers to a method in which glow discharge plasma is generated using the analytical sample as the cathode under a high-purity argon atmosphere, and the surface of the analytical sample is sputtered within the plasma. The constituent elements in the ionized analytical sample are then determined using a mass spectrometer. Thus, impurity elements, primarily n-type dopants, other than Ga and As contained in the GaAs single-crystal substrate can be qualitatively and quantitatively identified.

[0063] The GDMS described above is performed according to the following procedure. First, a GaAs single-crystal substrate 1 is obtained using the manufacturing method described later. Then, an analytical sample with a square diameter of 2 mm and a length of 20 mm is prepared by cleaving or the like on the GaAs single-crystal substrate 1. Next, the analytical sample is placed in the sample placement section attached to the GDMS apparatus. Here, the sample placement section is cleaned using conventional methods and pre-sputtered for 60 minutes to prevent foreign matter contamination and to remove foreign matter.

[0064] Next, GDMS was performed on the above-described analytical sample under the following conditions. Furthermore, the element acting as an n-type dopant in the analytical sample can be calculated as a semi-quantitative value by correcting the Ga to As ionic strength ratio using a relative sensitivity factor (RSF). The relative sensitivity factor can be a value built into the software accompanying the apparatus described below. For example, the GDMS measurement conditions for GaAs single-crystal substrate 1 are as follows.

[0065] Apparatus: Glow discharge mass spectrometer (trade name (model): VG-9000, manufactured by VG Elemental)

[0066] Ion source: needle-shaped element (cooled by liquid nitrogen during analysis)

[0067] Discharge area: 10mm in diameter

[0068] Discharge gas: High-purity argon (6N grade)

[0069] Discharge conditions: 2mA, 1kV (constant current mode)

[0070] Detectors: Faraday cup and multiplier

[0071] Quality resolution: 4000 or higher m / Δm (high resolution mode)

[0072] <Carrier Concentration>

[0073] GaAs single crystal substrate 1 can have 3.5 × 10⁻⁶ 18 cm -3 Above and 5.0×10 18 cm -3 The following carrier concentrations are given. GaAs single-crystal substrate 1 can have a carrier concentration of 3.6 × 10⁻⁶. 18 cm -3 Above and 4.9×10 18 cm -3 The carrier concentrations described below can also be 3.7 × 10⁻⁶. 18 cm -3 Above and 4.8×10 18 cm -3 The following are the carrier concentrations. When the carrier concentration is within the above range, the activation rate of the n-type dopant can be easily controlled to about 50% in relation to the atomic concentration of the n-type dopant in the GaAs single crystal substrate 1.

[0074] The carrier concentration of GaAs single-crystal substrate 1 was determined by Hall effect measurement at 25°C using the Van der Pauw method. (Refer to...) Figure 1 and Figure 2 The steps for determining the above carrier concentration are explained in detail. First, as follows... Figure 1 As shown, a GaAs single crystal obtained based on, for example, the manufacturing method described later, is processed using a conventionally known method to obtain a GaAs single crystal substrate 1, which is the object of measurement. A rectangular slice 11a (e.g., 650 μm thick) with dimensions 4 mm long × 4 mm wide is fabricated from the central portion of this GaAs single crystal substrate 1, with its center (e.g., the center of the main surface 11) as its center O. Next, as... Figure 2As shown, electrodes 21 made of an alloy containing gold, nickel, and germanium are formed at the four corners of the rectangular slice 11a (the measurement surface), thereby obtaining a sample for Hall measurement. Here, the shape of the electrode 21 is not limited to the rectangle shown in the figure, and can be a sector or a circle. The rectangular slice 11a having such electrodes 21 is subjected to Hall measurement using the Vander Pauw method in an environment of 25°C, thereby obtaining the carrier concentration. In addition, in this specification, the carrier concentration obtained based on taking the above rectangular slice as the measurement object is defined as the carrier concentration of the GaAs single crystal substrate.

[0075] <Activation rate of n-type dopant>

[0076] The GaAs single crystal substrate 1 may have an activation rate of the above n-type dopant of 40% or more and 60% or less. The GaAs single crystal substrate 1 may have an activation rate of the above n-type dopant of 45% or more and 55% or less. In this case, for the above reasons, it is possible to provide a GaAs single crystal substrate 1 with good yield that can reduce performance degradation caused by exposure to radiation or the like.

[0077] The activation rate of the n-type dopant is obtained from the ratio of the above carrier concentration of the GaAs single crystal substrate 1 to the atomic concentration of the n-type dopant, and is expressed as a percentage. Specifically, it is obtained by substituting the carrier concentration of the GaAs single crystal substrate 1 and the atomic concentration of the n-type dopant into the formula (activation rate of n-type dopant, %) = (carrier concentration) / (atomic concentration of n-type dopant) × 100.

[0078] <Boron (B)>

[0079] The GaAs single crystal substrate 1 may contain B. The GaAs single crystal substrate 1 may have an atomic concentration of the above B of 4.0×10 18 cm -3 or more and 6.0×10 18 cm -3 or less. B is introduced into the Ga site in the lattice of the GaAs single crystal, and thus competes with the n-type dopant introduced into this Ga site. Therefore, when the GaAs single crystal substrate 1 contains B in the above atomic concentration range, the n-type dopant easily enters the As site. In this case, B helps to reduce the carrier concentration in the GaAs single crystal substrate 1 and control the activation rate of the n-type dopant in the GaAs single crystal substrate 1.

[0080] B comes from the B2O3 melt that partially covers the first melt in which the n-type dopant is dissolved in the GaAs melt in the manufacturing method of the GaAs single crystal described below. B improves the strength of the GaAs single crystal, and thus has the effect of suppressing the ejection of atoms during radiation exposure. However, when the atomic concentration of B is greater than 6.0×1018 cm -3 In this case, because the GaAs single crystal substrate 1 contains boron arsenide, it may adversely affect the optical properties. The atomic concentration of B mentioned above can be determined using the GDMS measurement method described above.

[0081] <Absorption coefficient of infrared light with a wavelength of 1 micrometer>

[0082] In the GaAs single-crystal substrate 1, the absorption coefficient of infrared light at a wavelength of 1 micrometer (hereinafter also referred to as "near-infrared light absorption coefficient after electron beam irradiation"), measured after electron beam irradiation of at least one side of the main surface 11 under accelerating voltage of 2 MeV and irradiation dose of 150 kGy, is 95% or more and 100% or less of the absorption coefficient of infrared light at a wavelength of 1 micrometer (hereinafter also referred to as "near-infrared light absorption coefficient before electron beam irradiation") of the GaAs single-crystal substrate 1 before electron beam irradiation. In this case, the value of the near-infrared light absorption coefficient before electron beam irradiation can be 3.6 cm⁻¹. -1 The above. The near-infrared light absorption coefficient before electron beam irradiation can be 4.2 cm⁻¹. -1 The near-infrared absorption coefficient after electron beam irradiation is 3.6 cm⁻¹. -1 Above and 4.4cm -1 The following applies. When the near-infrared light absorption coefficient is within the range described above before electron beam irradiation, for example, if the optical device is used as a light sensor or the like through the GaAs single crystal substrate 1, the light absorption of the GaAs single crystal substrate 1 can be suppressed. Therefore, it may be possible to reduce the amount of grinding on the back side of the substrate or to mitigate defects such as breakage during back side grinding.

[0083] The aforementioned absorption coefficient can be obtained using conventionally known methods by measuring the transmittance and reflectance of light relative to the material using a UV-Vis-IR spectrophotometer or similar instrument. However, when obtaining the transmittance and reflectance of light using a UV-Vis-IR spectrophotometer or similar instrument for the GaAs single-crystal substrate 1, it is necessary to consider multiple reflections occurring between the two parallel main surfaces. Therefore, the aforementioned absorption coefficient can be obtained using the following method: Using a UV-Vis-IR spectrophotometer, near-infrared light with a wavelength of 1 micrometer is incident at an angle of 85 degrees to the center O of the main surface 11 of the GaAs single-crystal substrate 1, and the transmittance and reflectance of the near-infrared light of the GaAs single-crystal substrate 1 are measured. Furthermore, by substituting the values ​​of the aforementioned transmittance, the aforementioned reflectance, and the thickness of the GaAs single-crystal substrate 1 into Equations 1, 2, and 3 below, the aforementioned absorption coefficient, along with the reflectance of the near-infrared light of the GaAs single-crystal substrate 1 during a single reflection, is obtained.

[0084]

[0085]

[0086]

[0087] In equations 1, 2, and 3 above,

[0088] R* represents the reflectance considering multiple reflections, measured using the above-mentioned UV-Vis-IR spectrophotometer. The unit of the above reflectance is dimensionless.

[0089] T* represents the transmittance considering multiple reflections, measured using the aforementioned UV-Vis-IR spectrophotometer. The unit of the transmittance is dimensionless.

[0090] α represents the light absorption coefficient mentioned above, and the unit of the light absorption coefficient is cm. -1 .

[0091] R represents the reflectivity of the GaAs single crystal substrate 1 during a single reflection of near-infrared light, and the unit of the reflectivity during a single reflection is dimensionless.

[0092] d represents the thickness of the GaAs single crystal substrate 1, and the unit of the thickness is cm.

[0093] The following is for reference Figure 1 The steps for determining the absorption coefficient are explained in detail below. First, a GaAs single crystal obtained by, for example, the manufacturing method described later, is processed using a conventionally known method to obtain two GaAs single crystal substrates 1, which are to be measured. Two rectangular slices 11a (e.g., 650 μm thick), each with dimensions of 20 mm in length and 20 mm in width, are fabricated from these two GaAs single crystal substrates 1, with the center O of their main surface 11 as the center. These slices are used as samples for measuring the absorption coefficient. Then, the center of the surface of one of the samples (corresponding to the center O of the main surface 11 in the GaAs single crystal substrate 1) is irradiated with an electron beam under the conditions of an accelerating voltage of 2 MeV and an irradiation dose of 150 kGy. The angle of the electron beam incident on the surface is set to be perpendicular to the center O.

[0094] Next, using a UV-Vis-IR spectrophotometer (trade name (model): "U-4000", manufactured by Hitachi High Technology Co., Ltd.) and its accompanying absolute reflectance measurement unit, near-infrared light with a wavelength of 1 micrometer was incident at an angle of 85 degrees (5 degrees perpendicular to the main surface 11) onto the center of the surfaces of both the sample irradiated by the electron beam and the sample not irradiated by the electron beam. This allowed for the measurement of the near-infrared transmittance and reflectance of the GaAs single-crystal substrate 1 before and after electron beam irradiation. The transmittance and reflectance were obtained as measured values ​​of multiple reflections between the two parallel main surfaces 11 of the GaAs single-crystal substrate 1 (i.e., the front and back sides). Finally, the absorption coefficient was determined by repeatedly calculating the transmittance, reflectance, and thickness of the rectangular slice using Equations 1, 2, and 3, which take multiple reflections into account. Furthermore, the absorption coefficient was calculated together with the reflectance of the main surface 11 of the GaAs single-crystal substrate 1 during a single reflection. The aforementioned "reflectivity during a single reflection" refers to the reflectivity obtained based on the initial transmission and reflection of incident near-infrared light by the main surface 11 of the GaAs single-crystal substrate 1. In this specification, the absorption coefficient obtained by using the aforementioned rectangular slice 11a as the measurement object is defined as the absorption coefficient of the GaAs single-crystal substrate 1 for near-infrared light with a wavelength of 1 micrometer. Furthermore, the aforementioned equations 1 and 2, which consider multiple reflections, are convergent values ​​of an infinite geometric series assuming infinite reflections.

[0095] <Dislocation Density>

[0096] GaAs single crystal substrate 1 can have 1000 cm -2 The following dislocation density. GaAs single crystal substrate 1 can have 500 cm⁻¹. -2 The following dislocation density. In particular, the GaAs single-crystal substrate 1 contains at least Si as the above-mentioned n-type dopant and has a dislocation density of 2.0 × 10⁻⁶. 18 cm -3 With the above-mentioned atomic concentration of Si, it is possible to have 100 cm⁻¹ -2 The following dislocation density. In this case, the GaAs single-crystal substrate 1 can have a dislocation density of less than 100 cm⁻¹. -2 The dislocation density can also be 50cm. -2 The following dislocation density. Therefore, because of the low dislocation density, it is possible to provide a GaAs single-crystal substrate with excellent optical properties 1.

[0097] In this specification, "dislocation density" refers to the etch pit density (EPD) measured by the following method. Specifically, the "dislocation density" refers to the density of dislocations formed per 1 cm² on the main surface 11 during an etching test in which the GaAs single-crystal substrate 1 is immersed in molten potassium hydroxide at 500°C for 10 minutes. 2 The number of etching pits (corrosion pits). The method for measuring EPD described above is roughly as follows. First, a GaAs single crystal substrate 1, which is the object of measurement, is obtained based on, for example, the manufacturing method described later. Next, after mirror polishing its main surface (e.g., main surface 11), the GaAs single crystal substrate 1 is immersed in a potassium hydroxide (KOH) molten solution at 500°C for 10 minutes, forming the aforementioned etching pits on the main surface 11. Here, for the mirror-polished main surface 11, in order to clearly show the aforementioned etching pits, at least one of the following pretreatments—using sulfuric acid and hydrogen peroxide, or using ammonia and hydrogen peroxide—can be performed before immersion in the potassium hydroxide (KOH) molten solution for 10 minutes. The aforementioned etching pit density is not academically synonymous with dislocation density, but in this technical field, it can be considered equivalent to dislocation density (an intermediate indicator in industry).

[0098] Next, a grid of 5mm × 5mm squares is formed on the entire surface of the main surface 11 of the GaAs single crystal substrate 1 taken from the aforementioned molten potassium hydroxide, arranged in a manner that maximizes the number of non-overlapping squares. This grid divides the main surface 11. For example, the grid can be formed by drawing directly on the substrate with a pen or the like. Then, each square constituting the grid on the main surface 11 is used as a field of view, and the number of etch pits present in this field of view is counted using a known optical microscope (e.g., trade name: "ECLIPSE (registered trademark) LV150N", manufactured by Nikon Corporation). Finally, the number of etch pits present in each field of view is converted to a per 1cm... 2 The quantity. Therefore, each 1cm 2 The number of erosion pits was obtained in the same way as the number of squares that make up the lattice, so the above is calculated for every 1cm. 2 The sum of the number of etch pits divided by the number of squares is used to calculate the EPD (dislocation density) of the GaAs single-crystal substrate 1. Furthermore, if the outer periphery and outer side of the main surface 11 appear within the field of view, this field of view is excluded from the calculation of EPD. This is because the number of etch pits in the region near the outer periphery of the GaAs single-crystal substrate 1 varies greatly in each substrate and is typically a region of material not used for optical devices.

[0099] <Applications>

[0100] The GaAs single-crystal substrate 1 of this embodiment can be used as a substrate for optical devices such as semiconductor lasers (e.g., vertical-cavity surface-emitting lasers, light-receiving elements, etc.). In particular, based on the features described above, it can be used as a substrate for optical devices intended for use in environments easily exposed to radiation, such as the space environment.

[0101] [Manufacturing methods for GaAs single crystals]

[0102] The method for manufacturing GaAs single crystals in this embodiment can be, for example, the method for manufacturing GaAs single crystals used in the GaAs single crystal substrate described above. That is, the manufacturing method described above can be a method for manufacturing GaAs single crystals with an n-type conductivity using the vertical boat method. The manufacturing method described above includes the following steps: preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; accommodating a seed crystal formed from the GaAs single crystal at the bottom of the crucible, and accommodating an n-type dopant, B2O3, metallic arsenic (As), and a bulk or powdered GaAs polycrystal at a position higher than the seed crystal within the crucible; heating the crucible with the heating device to sublimate the metallic As, while simultaneously melting the B2O3 into a B2O3 molten liquid, melting a portion of the seed crystal and the GaAs polycrystal into a GaAs molten liquid, and obtaining a first molten liquid containing the n-type dopant dissolved in the GaAs molten liquid, and contacting the first molten liquid with the remaining portion of the seed crystal; and growing a crystal from the first molten liquid on the remaining portion of the seed crystal, thereby obtaining the GaAs single crystal. Hereinafter, the upward and downward directions along the axis of the crucible will be referred to as the upward direction and the downward direction, respectively. When describing the position or arrangement of the structure, the position in the upward direction will be called the upper part, and the position in the downward direction will be called the lower part.

[0103] The aforementioned single crystal growth apparatus includes a branch section (hereinafter also referred to as "As partial pressure control section") for controlling the As partial pressure within the crucible. In the process of obtaining the GaAs single crystal, the end face of the first melt that does not contact the remaining portion of the seed crystal is covered by the B2O3 melt with an area percentage of 10% to 50% or less. In the process of obtaining the GaAs single crystal, the GaAs in the first melt has a stoichiometric ratio of As to Ga exceeding 1. In particular, in the aforementioned GaAs single crystal manufacturing method, the crucible may not be rotated and the first melt may not be stirred during the GaAs single crystal obtaining process.

[0104] According to the GaAs single crystal manufacturing method of this embodiment, during the manufacturing of GaAs single crystals using the vertical boat method, the activation rate of the n-type dopant in the GaAs single crystal is made to about 50% by controlling the amount of n-type dopant added and the As partial pressure in the crucible. Specifically, during the manufacturing of the GaAs single crystal, the end face of the first melt that is not in contact with the remaining portion of the seed crystal is covered by B2O3 melt by 10% to 50% of its area. Furthermore, in the As partial pressure control unit of the single crystal growth apparatus, by controlling the As partial pressure in the crucible, the sublimated metallic As dissolves in the first melt in a necessary amount, thereby giving the GaAs in the first melt a stoichiometric ratio of As to Ga exceeding 1. When the end face is completely covered by B2O3 melt, As partial pressure control by the As partial pressure control unit of the single crystal growth apparatus is not possible. Even when the aforementioned end face is not completely covered by the B2O3 molten liquid, As partial pressure control can be performed by the aforementioned As partial pressure control section, but B, which increases crystal strength, is not added. According to the GaAs single crystal manufacturing method of this embodiment, by simultaneously performing partial coating of the aforementioned end face using the B2O3 molten liquid and As partial pressure control, the occupancy positions of Si and B in the first molten liquid and in the GaAs single crystal can be controlled, and their concentrations increase, reducing atomic ejection due to exposure to radiation. With this manufacturing method, GaAs single crystals that reduce performance degradation caused by exposure to radiation, etc., can be obtained.

[0105] The following is based on reference Figures 3-4 This embodiment describes in detail the method for manufacturing a GaAs single crystal and the method for manufacturing a GaAs single crystal substrate including this method. Figure 3 This is a flowchart illustrating a general method for manufacturing a GaAs single crystal and a GaAs single crystal substrate according to this embodiment. Figure 4 The method for manufacturing GaAs single crystals according to this embodiment is illustrated by a diagram showing the process of growing GaAs single crystals using a single crystal growth apparatus.

[0106] The method for manufacturing GaAs single crystals with n-type conductivity in this embodiment uses the vertical boat method. The vertical boat method includes, for example, the vertical Bridgman (VB) method, the vertical temperature gradient (VGF) method, and a hybrid method combining the VB and VGF methods. Hereinafter, a method for manufacturing GaAs single crystals using, for example, the VB method will be described. The above manufacturing method is, for example, a method for manufacturing GaAs single crystals using the VB method, such as... Figure 3As shown, it may include: a step (preparation step) S10 of preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; and a step S20 of growing a GaAs single crystal from a seed crystal by crystal growth using the single crystal growth apparatus.

[0107] The process S20 for growing GaAs single crystals may include: a process (raw material containment process) S21 in which a seed crystal formed from the GaAs single crystal is contained at the bottom of the crucible, and an n-type dopant, B2O3, metallic As, and a bulk or powdered GaAs polycrystalline material are contained at a position higher than the seed crystal within the crucible; a process (raw material melting and contact process) S22 in which the metallic As is sublimated by heating the crucible with the heating device, while the B2O3 is melted into a B2O3 molten liquid, a portion of the seed crystal and the GaAs polycrystalline material are melted into a GaAs molten liquid, and a first molten liquid containing the n-type dopant is obtained, and the first molten liquid is brought into contact with the remaining portion of the seed crystal; and a process (gaAs single crystal obtaining process) S23 in which a crystal is grown from the first molten liquid on the remaining portion of the seed crystal. Figure 3 The method for manufacturing a GaAs single crystal substrate according to the present embodiment, described later, can be constructed by a preparation step S10, a step S20 for growing a GaAs single crystal, and a step S30 for processing the GaAs single crystal obtained by the above manufacturing method to obtain a GaAs single crystal substrate.

[0108] <Preparation Process>

[0109] In the process of preparing the single crystal growth apparatus (preparation process) S10, for example, are prepared. Figure 4 The single crystal growth apparatus 10 shown includes a crucible 5 and a heating device 73. Furthermore, in the preparation step S10, seed crystals 8a, such as bulk metallic As and bulk or powdered GaAs polycrystals, are prepared together with the single crystal growth apparatus 10 as materials for growing GaAs single crystals 81. The seed crystal 8a is formed from a GaAs single crystal. The seed crystal 8a and the GaAs polycrystal can be prepared by known methods or by obtaining commercially available products. The seed crystal 8a may have a cylindrical shape capable of being accommodated in the seed crystal receiving portion 51 of the crucible 5 (described later). The GaAs polycrystal may have a size capable of being accommodated in at least the cylindrical portion 53 of the crucible 5 (described later).

[0110] (Single crystal growth apparatus)

[0111] 1) Crucible

[0112] like Figure 4 As shown, the single crystal growth apparatus 10 includes a crucible 5. The crucible 5 may include a cylindrical seed crystal receiving portion 51 for receiving a seed crystal 8a formed from a GaAs single crystal, an enlarged diameter portion 52 connected to the seed crystal receiving portion 51, and a straight cylindrical portion 53 connected to the enlarged diameter portion 52. The seed crystal receiving portion 51 has a hollow portion with an opening at the location connected to the enlarged diameter portion 52 and a bottom wall formed at the location opposite to the enlarged diameter portion 52. The seed crystal receiving portion 51 is capable of receiving and holding the seed crystal 8a within the hollow portion. The enlarged diameter portion 52 has a frustum-shaped diameter that expands along the upward direction of the crucible 5, and is connected to the seed crystal receiving portion 51 on the smaller diameter side of the enlarged diameter portion 52. The straight cylindrical portion 53 has a hollow cylindrical shape and is connected to the larger diameter side of the enlarged diameter portion 52. The enlarged diameter portion 52 and the straight cylindrical portion 53 function to hold a GaAs polycrystal, which is the material used to obtain the GaAs single crystal 81 through crystal growth, within their interiors. The expanded diameter section 52 and the straight cylindrical section 53, as described later, have the function of growing GaAs single crystals by solidifying the first melt 82 containing GaAs molten liquid and n-type dopant. The crucible 5 can be made of various materials capable of withstanding the temperature of the first melt 82. For example, the material of the crucible 5 is pyrolytic boron nitride (PBN).

[0113] The maximum inner diameter of crucible 5 is 100 mm or more. More specifically, the inner diameter of the straight cylindrical portion 53 of crucible 5 can be 100 mm or more. The inner diameter of the straight cylindrical portion 53 of crucible 5 can be 150 mm or more. There is no particular upper limit to the maximum inner diameter of crucible 5, for example, it can be 210 mm.

[0114] 2) Keep the platform

[0115] The single crystal growth apparatus 10 has a holding stage 71 for holding the expanded diameter portion 52 of the crucible 5. The holding stage 71 can have, for example, a cylindrical shape. The holding stage 71 can be formed from a single material. This material can be, for example, quartz, alumina, or silicon carbide. The material can be formed from quartz. Particularly considering heat conduction in the crucible and the GaAs molten liquid, the material can be opaque. The outer diameter of the holding stage 71 can correspond to, or be the same as, the outer diameter of the cylindrical portion 53.

[0116] 3) Heating device

[0117] The single crystal growth apparatus 10 includes a heating device 73 for heating the crucible 5. Sometimes, two heating devices 73 are configured. In this case, the two are arranged to surround the outer periphery of the crucible 5. Each of the heating devices 73 is divided into multiple sections in a direction perpendicular to the axis of the crucible. Thus, each of the heating devices 73 can be configured with multiple segments. Furthermore, the output power of each heating device 73 can be controlled independently for each and each section. Therefore, the temperature at the interface between the GaAs single crystal 81 and the first molten liquid 82 can be precisely controlled. As the heating device 73, a known electric heater is sometimes used.

[0118] The single crystal growth apparatus 10 can be equipped with thermocouples capable of measuring the temperature of the crucible 5 heated by the heating device 73. Sometimes, multiple thermocouples are arranged axially along the outer side of the crucible 5. In this case, multiple thermocouples can be arranged at least axially along the outer side of the crucible 5, near a height corresponding to the interface between the GaAs single crystal 81 and the first molten liquid 82 within the crucible 5. Based on the temperatures measured by the thermocouples, the temperature at various points of the GaAs single crystal 81 undergoing crystal growth within the crucible 5 can be estimated. In particular, based on the temperatures measured by the thermocouples, the radial temperature distribution at the aforementioned interface can be estimated.

[0119] 4) Branch pipe section (As pressure control section)

[0120] The single crystal growth apparatus 10 includes an As partial pressure control unit 9 for controlling the As partial pressure within the crucible 5. For example, the As partial pressure control unit 9 is positioned axially opposite to the seed crystal receiving portion 51. The As partial pressure control unit 9 controls the As partial pressure within the crucible 5 during the GaAs single crystal formation process S23. Specifically, through the action of the As partial pressure control unit 9, the temperature within the crucible 5 is controlled to a minimum during the GaAs single crystal formation process S23. Consequently, the metallic As9a that sublimates and precipitates on the sidewalls and upper walls of the crucible 5 during the heating of the crucible 5 in the raw material melting and contact process S22 dissolves in the first melt 82 in the GaAs single crystal formation process S23 at an As pressure of, for example, 101 kPa at 1238°C. At this time, the stoichiometric ratio of As to Ga single crystal 81 in the first melt 82 containing the GaAs melt is greater than 1 for both As and Ga. Figure 4 As shown, to facilitate temperature control within the crucible 5 by the As partial pressure control unit 9, an insulating material 91 can be disposed adjacent to the As partial pressure control unit 9. As the insulating material 91, for example, a known insulating material used for temperature control of crucibles in the vertical crystal boat method can be used. Therefore, the n-type dopant in the first molten liquid 82 can be easily introduced into the Ga sites in the lattice of the GaAs single crystal, thus enabling control of the activation rate of the n-type dopant. The As partial pressure control unit 9 can be formed of, for example, the same material as the crucible 5.

[0121] <Processes for growing GaAs single crystals>

[0122] Next, in the above manufacturing method, step S20 is performed whereby a GaAs single crystal is grown from a seed crystal using the aforementioned single crystal growth apparatus. Specifically, in step S20, a GaAs single crystal 81 is grown using the aforementioned single crystal growth apparatus 10 and a seed crystal 8a. Step S20 includes the following steps: raw material containment step S21, raw material melting and contact step S22, and step S23, which yields the GaAs single crystal. These steps in step S20 are performed in this order.

[0123] (Raw material receiving process)

[0124] In the raw material containing process S21, a seed crystal 8a made of GaAs single crystal is contained in the hollow portion of the seed crystal containing portion 51 of the crucible 5. The method for containing the seed crystal 8a in the seed crystal containing portion 51 can be, for example, a known method. Furthermore, multiple GaAs polycrystals are contained and stacked in the expanded diameter portion 52 and the cylindrical portion 53 of the crucible 5. As metal for arsenic pressure control, and at least one of Si, Te, and Sn as an n-type dopant, are added to the expanded diameter portion 52 and the cylindrical portion 53 of the crucible 5 along with the GaAs polycrystals. Then, solid B2O3 is contained on the GaAs polycrystals. In this case, the atomic concentration of the aforementioned n-type dopant in the GaAs single crystal 81 obtained by crystal growth can be 5.8 × 10⁻⁶. 18 cm -3 Above and 1.3×10 19 cm -3 The following amounts are added. Solid B2O3 can be contained in the following amounts: when B2O3 melt 6 is made in the process of obtaining GaAs single crystal described later, the end face of the first melt 82 that does not contact the remaining part of the seed crystal 8a is covered by B2O3 melt 6 with an area percentage of 10% or more and an area percentage of 50%.

[0125] (Raw material melting and contact process)

[0126] In the raw material melting and contacting process S22, in order to obtain GaAs single crystal 81, seed crystal 8a is brought into contact with a first melt 82 in which an n-type dopant is dissolved in GaAs melt. In the raw material melting and contacting process S22, a crucible 5 containing seed crystal 8a, GaAs polycrystalline material, n-type dopant, metallic As, and solid B2O3 is supported by a holding platform 71. Then, an electric current is supplied to the heating device 73 to heat the crucible 5. As a result, the GaAs polycrystalline material melts, and the n-type dopant dissolves therein to form the first melt 82. The bulk metallic As disposed near the GaAs polycrystalline material sublimates. Then, metallic As9a precipitates on the sidewalls and top wall of the crucible 5, where the temperature is low. Furthermore, a portion of seed crystal 8a also melts, and the remaining portion of seed crystal 8a contacts the first melt 82 at its interface. Solid B2O3 also melts to form B2O3 melt 6. The B2O3 molten liquid 6 is located above the first molten liquid 82 due to the difference in specific gravity.

[0127] (Process for obtaining GaAs single crystals)

[0128] In step S23, which yields the GaAs single crystal, the crucible 5 is slowly lowered relative to the heating device 73 in the downward direction (towards the seed crystal container 51), thereby creating a temperature gradient in the crucible 5 such that the temperature is lower on the seed crystal 8a side and higher on the first melt 82 side. As a result, the first melt 82 in contact with the seed crystal 8a solidifies, and the GaAs single crystal 81 is continuously crystallized from the first melt 82 on the remaining portion of the seed crystal 8a. The downward descent speed of the crucible 5 is not particularly limited, for example, it is 1 to 5 mm / hour.

[0129] In step S23, which yields GaAs single crystals, the end face of the first melt 82 that is not in contact with the remaining portion of the seed crystal 8a is covered by B2O3 melt 6 with an area percentage of 10% to 50% or less. Specifically, when the first melt 82 is heated by the heating device 73, the aforementioned end face has an upwardly convex shape, with the top of the end face exposed from the B2O3 melt 6. Thus, only the peripheral portion around the top is covered by B2O3 melt 6. The phrase "the end face is covered by B2O3 melt 6 with an area percentage of 10% to 50% or less" means that, of the aforementioned end face, the peripheral portion has an area percentage of 10% to 50% or less, and the top portion has an area percentage of 50% to 90% or less.

[0130] Furthermore, in step S23 of obtaining GaAs single crystal, As in the first melt 82 is controlled by the top portion of the end face that is not covered by B2O3 melt 6, which is at least 50% and less than 90% of the area. Specifically, by keeping the temperature of the As partial pressure control section 9 at its lowest within the crucible 5, the As pressure corresponding to the temperature of the As partial pressure control section 9 acts towards the end face in the first melt 82. As described above, due to the action of the As partial pressure control section 9, the amount of arsenic pressure that becomes 101 kPa at 1238°C in the As precipitated metal As9a on the sidewalls and upper walls of the crucible 5 is dispersed in the crucible 5 and dissolved in the first melt 82. This results in the GaAs in the first melt 82 having a stoichiometric ratio of As to Ga exceeding 1, making it easier for n-type dopants in the first melt 82 to be introduced into Ga sites in the lattice of the GaAs single crystal 81, and enabling control of the activation rate of the n-type dopants.

[0131] In step S23 of obtaining GaAs single crystal, the crystal growth of GaAs single crystal 81 continues until the solidification of the first melt 82 remaining in the straight cylindrical portion 53 of the crucible 5 ends, as the crucible 5 descends downward relative to the heating device 73. Here, in step S23 of obtaining GaAs single crystal, from the viewpoint that light elements, namely B, in the first melt 82 are retained in the upper part of the first melt 82 by gravitational segregation, the crucible 5 does not need to be rotated, and the first melt 82 does not need to be stirred. This is because if the concentration of B mixed from the B2O3 melt 6 into the first melt 82 increases excessively, boron arsenide may precipitate in the first melt 82, potentially deteriorating the crystallinity of GaAs single crystal 81. Therefore, the atomic concentration of B in GaAs single crystal 81 can be controlled to 4.0 × 10⁻⁶. 18 cm -3 Above and 6.0×10 18 cm -3 The following steps are taken. Based on the above, GaAs single crystal 81 (e.g., its ingot) can be obtained. Then, the GaAs single crystal 81 inside crucible 5 is removed from crucible 5.

[0132] [Manufacturing methods for GaAs single-crystal substrates]

[0133] <Process S30 for obtaining GaAs single crystal substrate>

[0134] The method for manufacturing the GaAs single-crystal substrate in this embodiment is a method for manufacturing a GaAs single-crystal substrate with an n-type conductivity. For example... Figure 3As shown, the manufacturing method described above includes the following steps: step S30, which involves processing the GaAs single crystal obtained by the GaAs single crystal manufacturing method to obtain a GaAs single crystal substrate with a circular main surface. Specifically, step S30 for obtaining the GaAs single crystal substrate includes: a cutting step of cutting the GaAs single crystal 81 obtained by the GaAs single crystal manufacturing method into a disk shape to obtain a GaAs single crystal substrate precursor; and a peripheral grinding step of processing the outer periphery of the GaAs single crystal substrate precursor to obtain a GaAs single crystal substrate with a circular main surface. By using a manufacturing method with such characteristics, performance degradation caused by exposure to radiation can be reduced, and a GaAs single crystal substrate suitable for use as a substrate for optical devices intended for use in a space environment can be obtained.

[0135] The process S30 for obtaining a GaAs single crystal substrate includes a subsequent dicing process, an outer peripheral grinding process, and a polishing process, which may be described later as needed. These processes are sometimes performed in this order.

[0136] The slicing process involves slicing a disk-shaped GaAs single-crystal substrate precursor, formed from a GaAs single-crystal 81 ingot removed from crucible 5, into wafers of a specified thickness. The peripheral grinding process involves grinding the outer periphery of the GaAs single-crystal substrate precursor to obtain a GaAs single-crystal substrate with a circular main surface. Known slicing and peripheral grinding methods can sometimes be used as the slicing and grinding processes. The polishing process involves mirror-finishing the main surface. Known polishing methods can sometimes be used as the polishing process.

[0137] [Example]

[0138] The present invention will be further described in detail below with examples, but the invention is not limited thereto. In this embodiment, the inventors use, for example... Figure 4 The single crystal growth apparatus shown uses the VB method to... <100> The growth direction is used to guide the growth of GaAs single crystals. In the following description, samples 1 to 4 are examples, and samples A and B are comparative examples.

[0139] [Fabrication of GaAs single-crystal substrates]

[0140] <Sample 1>

[0141] (Preparation process)

[0142] First, prepare as follows Figure 4The single crystal growth apparatus is shown. Furthermore, a GaAs seed crystal formed from a GaAs single crystal and a bulk GaAs polycrystal are prepared using known methods. The GaAs seed crystal has a cylindrical shape that can be accommodated in a seed crystal receiving portion of a crucible. The GaAs polycrystal has a size that can be accommodated in a cylindrical portion. The inner diameter of the cylindrical portion of the crucible included in the above-described single crystal growth apparatus is 154 mm.

[0143] (The process of growing GaAs single crystals)

[0144] Following the aforementioned raw material containment process, raw material melting and contact process, and GaAs single crystal growth process, a process is implemented whereby a GaAs single crystal is grown from a GaAs seed crystal using the aforementioned single crystal growth apparatus. In the raw material containment process, Si, for example, is used as an n-type dopant at a concentration of 7.0 × 10⁻⁶. 18 cm -3 The atomic concentration of As was added to the crucible along with the GaAs polycrystal. Furthermore, to control the arsenic pressure, a quantity of metallic As with an arsenic pressure of 101 kPa at 1238°C was placed within the crucible volume. Additionally, 10 g of solid B₂O₃ was contained within the crucible. During the raw material melting and contact process, all of the aforementioned metallic As sublimated. In the process of obtaining the GaAs single crystal, in the first melt containing an n-type dopant dissolved in the GaAs melt, a peripheral portion representing 10% of the area of ​​the end face not in contact with the GaAs seed crystal was coated with molten B₂O₃. Here, when the temperature of the first melt not coated with B₂O₃ is set to T₁, the arsenic pressure at equilibrium with the GaAs (first melt) at temperature T₁ is set to P₁, the temperature of the branch section is set to T₂, and the vapor pressure of metallic As in the branch section at temperature T₂ is set to P₂, the higher the temperature T₂ of the branch section, the greater the vapor pressure P₂ of metallic As. Based on the above facts, in the process of obtaining GaAs single crystals, at the moment when all GaAs has dissolved, the partial pressure of As in the crucible is controlled by adjusting the temperature T2 of the branch pipe to the lowest temperature inside the crucible. Therefore, the stoichiometric ratio of GaAs in the first melt is greater than 1 for As relative to Ga. For example, the arsenic pressure P1 at equilibrium with GaAs at 1238°C, calculated as the sum of 4-atomic As molecules (As₄) and 2-atomic As molecules (As₂), is approximately 91 kPa. In this case, when the temperature T2 of the branch pipe is 613°C, the vapor pressure P2 of metallic As is 101 kPa. That is, because P2 > P1, the stoichiometric ratio of GaAs in the first melt is greater than 1 for As relative to Ga.

[0145] In the process of obtaining GaAs single crystals, the crucible is slowly lowered relative to the heating device at a speed of 4 mm / hour. The growth of the GaAs single crystal then continues until the molten liquid remaining in the cylindrical portion of the crucible has solidified. Based on the above, a GaAs single crystal ingot with a diameter of 154 mm and a thickness of 200 mm was manufactured.

[0146] (Process for obtaining GaAs single crystal substrate)

[0147] Using the aforementioned GaAs single crystal ingot, GaAs single crystal substrates of the required number, n-type conductivity and circular main surface, are manufactured from the aforementioned GaAs single crystal ingot according to the above-described process for obtaining GaAs single crystal substrates. The GaAs single crystal substrate of sample 1 has a diameter of 150 mm and a thickness of 650 μm.

[0148] <Sample 2 to Sample 4>

[0149] In the raw material containment process, the amount of Si added as an n-type dopant is varied as described in Table 1. Otherwise, GaAs single crystal substrates of the required number are manufactured according to the same method as the manufacturing method of GaAs single crystal substrate of sample 1.

[0150] <Sample A>

[0151] The GaAs single-crystal substrate of sample A was fabricated using the well-known horizontal Bridgman process (HB process). In this case, the atomic concentration of Si added to the GaAs molten metal as an n-type dopant is shown in Table 1. Furthermore, B2O3 was not used in the fabrication of the GaAs single-crystal substrate of sample A.

[0152] <Sample B>

[0153] In the raw material containment process, the amount of Si added as an n-type dopant is changed as described in Table 1. In the process of obtaining GaAs single crystals, the entire surface of the aforementioned end face of the first melt in which the n-type dopant is dissolved in GaAs melt is covered by B2O3 melt. Furthermore, the As partial pressure in the crucible is not actively controlled in the As partial pressure control section. Otherwise, the required number of GaAs single crystal substrates of sample B are manufactured according to the same method as the method for manufacturing the GaAs single crystal substrate of sample 1.

[0154] [Characteristic Evaluation of GaAs Single Crystal Substrates]

[0155] For the GaAs single-crystal substrates of samples 1 to 4, sample A, and sample B, the atomic concentration of Si, atomic concentration of B, carrier concentration, activation rate, dislocation density (EPD), absorption coefficient of infrared light at 1 μm wavelength before and after electron beam irradiation, and the ratio of absorption coefficients (absorption coefficient of infrared light at 1 μm wavelength after electron beam irradiation / absorption coefficient of infrared light at 1 μm wavelength before electron beam irradiation × 100) were determined using the above-described measurement and calculation methods. The results are shown in Table 1.

[0156] [Table 1]

[0157]

[0158] [Inspection]

[0159] As shown in Table 1, compared to samples A and B, the absorption coefficient of the GaAs single-crystal substrates of samples 1 to 4 before and after electron beam irradiation is 95% to 100% higher than that of infrared radiation at a wavelength of 1 micrometer. Therefore, the performance degradation caused by exposure to radiation can be reduced. This suggests that the GaAs single-crystal substrates of samples 1 to 4 can be used as substrates for optical devices intended for use in a space environment.

[0160] The embodiments and examples of the present invention have been described above, but from the outset a structure that appropriately combines the above embodiments and examples was planned.

[0161] The embodiments and examples disclosed herein should be considered as illustrative in all respects and not as limiting. The scope of the invention is not limited to the embodiments and examples described above but is shown by the scope of the claims, and is intended to include the meaning equivalent to the scope of the claims and all modifications within that scope.

[0162] Explanation of reference numerals in the attached figures

[0163] 1: GaAs single crystal substrate;

[0164] 11: Main surface;

[0165] 11a: Rectangular slice;

[0166] O: Center;

[0167] OF: Positioning flat edge;

[0168] 21: Electrode;

[0169] 10: Single crystal growth apparatus;

[0170] 5: Crucible;

[0171] 51: Seed crystal housing;

[0172] 52: Expanded diameter section;

[0173] 53: Straight section;

[0174] 6: Molten B2O3;

[0175] 71: Maintain the platform;

[0176] 73: Heating device;

[0177] 8a: Seed crystal;

[0178] 81: GaAs single crystal;

[0179] 82: First molten liquid;

[0180] 9: Branch pipe section (As pressure control section);

[0181] 9a: Metal As;

[0182] 91: Thermal insulation materials;

[0183] S10: Preparation process;

[0184] S20: The process for growing GaAs single crystals;

[0185] S21: Raw material receiving process;

[0186] S22: Raw material melting and contact process;

[0187] S23: The process for obtaining GaAs single crystals;

[0188] S30: The process of obtaining a GaAs single crystal substrate.

Claims

1. A gallium arsenide single-crystal substrate, wherein the conductivity type is electron-donating gallium arsenide single-crystal substrate, The gallium arsenide single crystal substrate has a circular main surface. The gallium arsenide single crystal substrate contains an electron-donating dopant. The absorption coefficient of the gallium arsenide single crystal substrate at a wavelength of 1 micrometer, measured after electron beam irradiation of at least one side of the main surface under the conditions of accelerating voltage of 2 MeV and irradiation dose of 150 kGy, is more than 95% and less than 100% of the absorption coefficient of the gallium arsenide single crystal substrate at a wavelength of 1 micrometer measured before electron beam irradiation.

2. The gallium arsenide single crystal substrate of claim 1, wherein, The gallium arsenide single crystal substrate has a 3.5 x 10 18 cm -3 above and 5.0 x 10 18 cm -3 below a carrier concentration, The gallium arsenide single crystal substrate has an activation rate of more than 40% and less than 60% for the electron-donating dopant.

3. The gallium arsenide single-crystal substrate according to claim 2, wherein, The gallium arsenide single crystal substrate has an activation rate of more than 45% and less than 55% for the electron-donating dopant.

4. The gallium arsenide single-crystal substrate according to any one of claims 1 to 3, wherein, The gallium arsenide single crystal substrate has an atomic concentration of 5.8 x 10 18 cm -3 The above and 1.3 x 10 19 cm -3 The atomic concentration of the electron-donor type dopant below.

5. The gallium arsenide single-crystal substrate according to any one of claims 1 to 3, wherein, The gallium arsenide single crystal substrate contains boron. The gallium arsenide single crystal substrate has an atomic concentration of boron of 1.0 x 10 18 cm -3 The above and 6.0 x 10 18 cm -3 The atomic concentration of boron below.

6. The gallium arsenide single-crystal substrate according to any one of claims 1 to 3, wherein, The value of the absorption coefficient of the wavelength 1 micrometer infrared ray of the gallium arsenide single crystal substrate measured before the electron beam irradiation was 3.6 cm -1 The above.

7. The gallium arsenide single-crystal substrate according to any one of claims 1 to 3, wherein, The electron-donating dopant is selected from at least one of silicon, tellurium, and tin.

8. The gallium arsenide single-crystal substrate according to any one of claims 1 to 3, wherein, The gallium arsenide single crystal substrate has a 1000 cm -2 The following dislocation density.

9. The gallium arsenide single-crystal substrate according to claim 8, wherein, The gallium arsenide single crystal substrate contains at least silicon as the electron-donating dopant. The gallium arsenide single crystal substrate has an atomic concentration of silicon of 2.0 x 10 18 cm -3 The atomic concentration of silicon above, The gallium arsenide single crystal substrate has a 100 cm -2 The following dislocation density.

10. A method for manufacturing gallium arsenide single crystals, which is a method for manufacturing gallium arsenide single crystals of the electron-donating conductivity type using a vertical crystal boat method. The manufacturing method includes the following steps: A process for preparing a single crystal growth apparatus having at least a cylindrical crucible and a heating device arranged to surround the outer periphery of the crucible; The process of accommodating a seed crystal formed from the gallium arsenide single crystal at the bottom of the crucible, and accommodating an electron-type dopant, boron oxide, metallic arsenic, and a bulk gallium arsenide polycrystal at a position higher than the seed crystal within the crucible; The process involves heating the crucible with the heating device to sublimate the metallic arsenic, simultaneously melting the boron oxide into a boron oxide molten liquid, melting a portion of the seed crystal and the gallium arsenide polycrystalline material into a gallium arsenide molten liquid, and obtaining a first molten liquid containing the electron-donating dopant dissolved in the gallium arsenide molten liquid, followed by contacting the first molten liquid with the remaining portion of the seed crystal; and... The process of growing a crystal from the first melt on the remaining portion of the seed crystal to obtain the gallium arsenide single crystal; The single crystal growth apparatus has a branch section for controlling the partial pressure of arsenic within the crucible. In the process of obtaining the gallium arsenide single crystal, the end face of the first molten metal that does not contact the remaining part of the seed crystal is covered by the boron oxide molten metal with an area percentage of 10% or more and an area percentage of less than 50%. In the process of obtaining the gallium arsenide single crystal, the gallium arsenide in the first melt has a stoichiometric ratio of arsenic to gallium of more than 1.

11. The method for manufacturing gallium arsenide single crystal according to claim 10, wherein, In the process of obtaining the gallium arsenide single crystal, the crucible is not rotated, and the first molten liquid is not stirred.

12. A method for manufacturing a gallium arsenide single crystal substrate, comprising the following steps: The process of processing the gallium arsenide single crystal obtained by the manufacturing method of gallium arsenide single crystal according to claim 10 or claim 11 to obtain a gallium arsenide single crystal substrate having a circular main surface.

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