Gallium oxide crystal, method for producing same, and use thereof

Abstract

The present invention provides: a gallium oxide crystal in which oxygen defects are suppressed; and a method for producing the same. A β-type gallium oxide crystal according to an embodiment of the present invention contains at least gallium (Ga), oxygen (O), and hydrogen (H), and has a crystal structure substantially identical to a β-Ga2O3 crystal. A method for producing a β-type gallium oxide crystal according to the present embodiment includes subjecting a raw material containing each element included in a crystal to crystal growth through hydrothermal synthesis in the presence of a mineralizer containing an alkali metal and / or an alkaline earth metal, or an acidic mineralizer, or a mixed mineralizer of both of the mineralizers.

Description

Gallium oxide crystal, its manufacturing method and use

[0001] The present invention relates to gallium oxide crystals, a method for producing the same, and uses thereof.

[0002] In recent years, gallium oxide (Ga) has been used as a semiconductor material for power devices. ２ O ３ ) is attracting attention. ２ O ３ It is known that GaAs has several types of crystal structures, among which the monoclinic β type (β-Ga ２ O ３ ) is said to be the most stable structure.

[0003] β-Ga ２ O ３ The EFG (Edge-defined Film-fed Growth) method is one of the techniques for growing bulk single crystals of β-Ga. However, in terms of the melting point and reactivity of gallium oxide, the EFG method requires the use of iridium (Ir) as a material for the crucible and die, and therefore, reducing the manufacturing cost is an issue for practical use. ２ O ３ Concerns have been raised about the crystal growth, such as the incorporation of Ir from the crucible into the crystal, and the need to grow the crystal under conditions where the oxygen partial pressure is controlled low to prevent oxidation of the Ir crucible, which can lead to oxygen defects inherent in the manufacturing process. These problems also apply to another growth technique, the Czochralski (CZ) method.

[0004] As a growth technique that does not use an Ir crucible, Patent Document 1 describes a method for growing β-Ga alloys by a VB (vertical Bridgman) method using a Pt / Rh alloy crucible. ２ O ３It has been proposed to grow a Pt / Rh alloy crystal. Here, the lower limit of the Rh (rhodium) content in the Pt / Rh alloy crucible must be 10 wt % or more, and since an excessively high Rh content causes the problem of Rh dissolving (the amount of Rh dissolved increases), it is considered desirable to set the Rh content to 30 wt % or less. According to the manufacturing method and manufacturing apparatus of Patent Document 1, conditions of an oxygen partial pressure of 10% to 50% can be applied, and Ga crystals can be grown by the VB method in the atmosphere. ２ O ３ However, even if the Pt / Rh alloy crucible has an adjusted Rh content, the crystals are likely to be grown in the atmosphere, especially when grown in air. ２ O ３ It is considered difficult to prevent Pt / Rh from dissolving into the melt and being incorporated into the crystal. Furthermore, with this method, the Pt / Rh alloy crucible cannot be reused, and the crucible must be remade after crystal growth. In addition, the high Rh content makes cost reduction an issue.

[0005] On the other hand, as a growth technique that does not use a crucible, the skull melt method is used in combination with the pulling method to grow β-Ga. ２ O ３There have been reports on growing crystals (see Non-Patent Documents 1 and 2). This method is characterized by the fact that it does not require a crucible and can be grown in air. However, since the growth condition must be stabilized by melting the center of the raw material using high-frequency induction heating while cooling the periphery, frequency control is important, especially for growing large crystals (see Patent Document 2). When growing crystals using the pulling method, it is necessary to have the lowest temperature directly below the seed crystal, i.e., at the center of the melt surface, and the temperature of the periphery be high in order to grow large bulk single crystals. However, with this technology, the temperature gradient is reversed. Therefore, in principle, it is difficult to grow large, high-quality single crystals. Although there is no mention of the theoretical impossibility of intentionally manipulating this temperature gradient and melt convection, there are significant doubts about actually achieving this, and it poses a significant cost challenge. In fact, according to previous reports, the crystals grown by the pulling method do not have the straight body portion that is usually seen in crystals grown by the pulling method, but rather have the appearance of a crystal of a certain size spreading out directly below the seed crystal.This method makes it difficult to create a temperature gradient in the melt that is suitable for crystal growth, and it is thought that it is difficult to grow bulk single crystals, let alone large ones.

[0006] JP 2017-193466 A JP 2023-122837 A

[0007] Taketoshi Tomita et al., A new method for growing crucible-free β-Ga2O3 single crystals by the skull melt method, Proceedings of the 69th Spring Meeting of the Japan Society of Applied Physics, February 25, 2022, p. 16-052; Akira Yoshikawa, A method for growing bulk oxide single crystals using a cold crucible without using a precious metal crucible, Journal of the Japanese Society for Crystal Growth, July 29, 2022, Vol. 49, No. 2 (2022)

[0008] The present invention has been made in view of these circumstances, and aims to provide a gallium oxide crystal in which oxygen defects are suppressed. Another aim of the present invention is to provide a method for producing the above-mentioned gallium oxide crystal under conditions of high oxygen partial pressure without using conventional components using Ir or Rh, such as crucibles or dies. Another aim of the present invention is to provide uses for the above-mentioned gallium oxide crystal.

[0009] The β-type gallium oxide crystal according to the present invention contains at least gallium (Ga), oxygen (O) and hydrogen (H), and is β-Ga ２ O ３ The β-type gallium oxide crystal of the present invention has a crystal structure substantially identical to that of the β-type gallium oxide crystal, and thereby solves the above-mentioned problems. １－ｘ M ｘ ) ２ O ３－ｙ (wherein M is at least one element selected from the group consisting of aluminum (Al) and indium (In), and x and y each independently satisfy 0≦x<0.8 and −0.5≦y≦0.5.) In the β-type gallium oxide crystal of the present invention, the hydrogen concentration may be 1×10 １６ atoms / cm ３ 1x10 or more ２３ atoms / cm ３ The concentration of the alkali metal and / or alkaline earth metal may be in the range of 1×10 to 1×10. The β-type gallium oxide crystal of the present invention may further contain at least one additional element D selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), iridium (Ir), magnesium (Mg), iron (Fe), copper (Cu), silver (Ag), zinc (Zn), and cadmium (Cd). The β-type gallium oxide crystal of the present invention may further contain an alkali metal and / or alkaline earth metal. The concentration of the alkali metal and / or alkaline earth metal may be in the range of 1×10 to 1×10. １２ atoms / cm ３ 1x10 or more ２０ atoms / cm ３ The β-type gallium oxide crystal of the present invention may further contain at least one halogen element selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The halogen element may include at least F. The halogen element may be F. The concentration of the halogen element may be 1×10 １６ atoms / cm ３ 1x10 or more ２３ atoms / cm ３ The following ranges may also be used:

[0010] The method for producing the above-mentioned β-type gallium oxide crystal according to the present invention comprises growing crystals by hydrothermal synthesis from raw materials containing each element contained in the crystal in the presence of a mineralizer containing an alkali metal and / or alkaline earth metal, or an acid mineralizer, or a mixed mineralizer of both, thereby solving the above-mentioned problem. The concentration of the mineralizer may be in the range of 1 M or more and 50 M or less. In growing the crystals by the hydrothermal synthesis method, the temperature may be in the range of 400 ° C or more and 800 ° C or less, and the maximum pressure may be in the range of 25 MPa or more and 250 MPa or less.

[0011] The semiconductor material according to the present invention comprises the above-described β-type gallium oxide crystal, thereby solving the above-described problems. The above-described semiconductor material may be a plate-shaped substrate. The semiconductor device according to the present invention includes a layer made of a semiconductor material comprising the above-described β-type gallium oxide crystal and / or the above-described plate-shaped substrate, thereby solving the above-described problems. The semiconductor device may be a diode or a switching element.

[0012] According to the present invention, there is provided a β-type gallium oxide crystal in which oxygen defects are suppressed. The defect-controlled β-type gallium oxide crystal of the present invention is suitable for use as a semiconductor material.

[0013] The β-type gallium oxide crystal of the present invention is produced by hydrothermal synthesis, which allows it to be grown at temperatures significantly lower than those of the conventional methods described above. In addition, bulk single crystals can be grown under conditions of high oxygen partial pressure (in an oxygen-rich atmosphere). As a result, the obtained crystals have the above-mentioned oxygen defects suppressed, resulting in defect-controlled crystals. Furthermore, the present invention eliminates the need to use conventional crucibles and dies containing Ir or Rh, thereby reducing the production cost of the target crystals. Furthermore, by using hydrothermal synthesis, it is relatively easy to increase the size of the crystals compared to conventional methods. The β-type gallium oxide crystal of the present invention produced in this manner can be cut from the bulk single crystal and polished to form a plate-shaped body, thereby forming a substrate that can be used as a wafer for semiconductor manufacturing. This substrate is suitable for use in various semiconductor devices.

[0014] 1 is a schematic diagram showing an example of a Schottky barrier diode (SBD) according to an embodiment of the semiconductor device of the present invention; FIG. 2 is a schematic diagram showing an example of a metal oxide semiconductor field effect transistor (MOSFET) according to an embodiment of the semiconductor device of the present invention; FIG. 3 is a schematic diagram showing another example of a MOSFET according to an embodiment of the semiconductor device of the present invention; ２ O ３ 1 is a SEM image of the crystals of Example 1 obtained in the examples. 2 is a microscopic image of the crystals of Example 4 obtained in the examples. 3 is a microscopic image of the crystals of Example 5 obtained in the examples. 4 is a SEM image of the crystals of Example 1 and the raw material β-Ga ２ O ３ 1 shows the results of EDX measurement of the crystal of Example 1 and the raw material β-Ga. ２ O ３ The powder X-ray diffraction measurement results of β-Ga ２ O ３ 1 is a diagram showing the results of simulation of the diffraction chart of the crystal of Example 4 and the raw material β-Ga (monoclinic system). ２ O ３ The powder X-ray diffraction measurement results of β-Ga ２ O ３ 1 is a diagram showing the results of simulation of the diffraction chart of the crystal of Example 5 and the raw material β-Ga (monoclinic system). ２ O ３ The powder X-ray diffraction measurement results of β-Ga ２ O ３ 1 is a diagram showing the results of simulation of the diffraction chart of (monoclinic system). FIG. 2 is a diagram showing the concentrations of hydrogen, fluorine, and cesium in the secondary ion mass spectrometry results of the crystal of Example 1.

[0015] Hereinafter, an embodiment of the present invention will be described.

[0016] [Gallium oxide crystal] A gallium oxide crystal according to one embodiment of the present invention is a gallium oxide crystal having a β-type crystal structure. Hereinafter, the gallium oxide crystal according to this embodiment will also be referred to as a "β-type gallium oxide crystal."

[0017] β-type gallium oxide crystal contains at least gallium (Ga), oxygen (O), and hydrogen (H) as constituent elements. Here, in the β-type gallium oxide crystal, a portion of Ga may be substituted with at least one element selected from the group consisting of aluminum (Al) and indium (In), which belong to the same Group 13 as Ga in the periodic table.

[0018] That is, in one embodiment, the β-type gallium oxide crystal has the general formula (Ga, M) ２ O ３ (wherein M is at least one element selected from the group consisting of Al and In). More specifically, the β-type gallium oxide crystal can be represented by the general formula (Ga １－ｘ M ｘ ) ２ O ３－ｙ (wherein M is at least one element selected from the group consisting of Al and In, and x and y each independently satisfy 0≦x<0.8 and −0.5≦y≦0.5.) In the above general formula, x may satisfy 0≦x≦0.5 or 0≦x<0.5.

[0019] In β-type gallium oxide crystals, the number of oxygen atoms may be less than or greater than 3 due to defects in the crystal, but by satisfying the condition of y in the general formula, -0.5≦y≦0.5, the deterioration of the properties as a semiconductor material is sufficiently suppressed. In other words, in the general formula, the value of y is preferably close to zero. Most preferably, y in the general formula is zero, and in this case, the β-type gallium oxide crystal is (Ga １－ｘ M ｘ ) ２ O ３ (wherein M is at least one element selected from the group consisting of Al and In, and x satisfies 0≦x<0.8). Note that in this composition as well, x may satisfy 0≦x≦0.5 or 0≦x<0.5.

[0020] In one embodiment, the concentration of hydrogen is 1×10 １６ atoms / cm ３1x10 or more ２３ atoms / cm ３ The range is preferably 1×10 １７ atoms / cm ３ 1x10 or more ２２ atoms / cm ３ The range is preferably 1×10 １８ atoms / cm ３ 1x10 or more ２２ atoms / cm ３ The range is as follows:

[0021] The method for measuring the hydrogen concentration in β-type gallium oxide crystals is not particularly limited, and can be confirmed by conventional methods, for example, secondary ion mass spectrometry (SIMS) can be used. The same applies to the concentrations of elements other than hydrogen (for example, the concentrations of optional constituent elements (alkali metals and / or alkaline earth metals, and halogen elements) described below). Here, when SIMS is used, the hydrogen concentration is the value at a depth of 3 μm, and the same applies to the concentrations of elements other than hydrogen. Note that SIMS measurement examples will be described in the Examples section.

[0022] <Additive element D> The β-type gallium oxide crystal may further contain, as a dopant (also referred to as an additive), an element other than the above-mentioned Ga, O, H, and M element (Al, In). In this specification, such an element contained as a dopant is also referred to as additive element D.

[0023] The additive element D can be appropriately selected depending on the application as a semiconductor material, the desired properties, etc. The additive element D may be one type alone or two or more types in combination. For example, when intended for use as an n-type semiconductor material, silicon (Si), germanium (Ge), tin (Sn), etc. can be used as the additive element D. When intended for use as a p-type semiconductor material, iridium (Ir), etc. can be used as the additive element D. Furthermore, when intended for use as a semi-insulating material or a highly insulating material, magnesium (Mg), iron (Fe), etc. can be used as the additive element D. Other examples of the additive element D include copper (Cu), silver (Ag), zinc (Zn), cadmium (Cd), etc.

[0024] In an embodiment in which the β-type gallium oxide crystal contains the above-mentioned additional element D, there is no particular limitation on the concentration of the additional element D. When the β-type gallium oxide crystal contains an appropriate additional element D at an appropriate concentration, a semiconductor material having desired properties can be obtained.

[0025] <Optional Constituent Elements> The β-type gallium oxide crystal may further contain optional constituent elements other than Ga, O, H, M elements (Al, In) and the additional element D described above.

[0026] In one embodiment, the β-type gallium oxide crystal further contains an alkali metal and / or alkaline earth metal as an optional constituent element. In one exemplary embodiment, the alkali metal is selected from the group consisting of lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), and francium (Fr), and among these, it is preferably selected from the group consisting of K, Rb, and Cs. The alkaline earth metal is selected from the group consisting of beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra), and among these, it is preferably selected from the group consisting of Ca, Sr, and Ba. The alkali metal and alkaline earth metal may be a single type or a combination of two or more types. It is expected that the inclusion of an alkali metal and / or alkaline earth metal in the β-type gallium oxide crystal will passivate defects within the crystal.

[0027] In an embodiment in which the β-type gallium oxide crystal contains an alkali metal and / or an alkaline earth metal, the concentration of the alkali metal and / or the alkaline earth metal is 1×10 １２ atoms / cm ３ 1x10 or more ２０ atoms / cm ３ The range is preferably 1×10 １３ atoms / cm ３ 1x10 or more １９ atoms / cm ３ More preferably, it is in the range of 1×10 １４ atoms / cm ３ 1x10 or more １８ atoms / cm ３ The range is as follows:

[0028] In one embodiment, the β-type gallium oxide crystal further contains a halogen element as an optional constituent element. In one exemplary embodiment, the halogen element is selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br), and iodine (I). The halogen element may be a single element or a combination of two or more elements. In a preferred embodiment, the halogen element includes at least F. In a more preferred embodiment, the halogen element is F. It is expected that the inclusion of a halogen element in the β-type gallium oxide crystal will passivate defects within the crystal. The concentration of the halogen element is preferably 1×10 １６ atoms / cm ３ 1x10 or more ２３ atoms / cm ３ More preferably, it is in the range of 1×10 １７ atoms / cm ３ 1x10 or more ２２ atoms / cm ３ The range is more preferably 1 × 10 １８ atoms / cm ３ 1x10 or more ２１ atoms / cm ３ The following ranges may be satisfied:

[0029] <Crystal Structure> The β-type gallium oxide crystal is the above-mentioned β-Ga ２ O ３ Specifically, the β-type gallium oxide crystal belongs to the monoclinic crystal system, the C12 / m1 space group (space group 12 in the International Tables for Crystallography (also simply referred to as the International Table(s))), and has the crystal parameters and atomic coordinate positions shown in Table 1.

[0030]

[0031] The lattice constant of β-type gallium oxide crystal changes when its constituent elements are replaced with other elements or when the added element D is dissolved in solid solution. However, the atomic positions given by the crystal structure, the sites occupied by the atoms, and their coordinates do not change so significantly that the chemical bonds between the skeletal atoms are broken.

[0032] [Method for Producing Gallium Oxide Crystals] Next, a method for producing the above-mentioned β-type gallium oxide crystals will be described.

[0033] A method for producing β-type gallium oxide crystals according to one embodiment of the present invention involves growing crystals by hydrothermal synthesis from a raw material containing gallium (Ga), optionally containing an element M (wherein M is at least one element selected from the group consisting of Al and In), and optionally containing an additional element D, in the presence of a mineralizer containing an alkali metal and / or alkaline earth metal, or an acid mineralizer, or a mixed mineralizer of both. Here, the term "hydrothermal synthesis" refers to an embodiment in which water is used as a solvent in a "solvothermal method." An example of this production method will be described below.

[0034] <Step S110: Step of Preparing Raw Materials> In step S110, raw materials necessary for obtaining a compound that satisfies the composition of the target crystal are prepared.

[0035] Specifically, at least a raw material containing Ga is prepared, and the raw material is an oxide. In addition, a raw material containing the element M and / or a raw material containing the additional element D is prepared as needed. For convenience, in this specification, the raw materials containing each constituent element prepared in step S110 will also be referred to as the raw materials of each constituent element. For example, "a raw material containing Ga" and "a Ga raw material" are synonymous.

[0036] As each raw material, a simple substance of a constituent element, an oxide, a hydroxide, a halide, an inorganic salt (sulfate, nitrate, carbonate, etc.), an organic salt (acetate, etc.), etc. can be used. Each compound other than a simple substance may be an anhydride or a hydrate. Below, non-limiting examples of usable raw materials for each constituent element that can be contained in the β-type gallium oxide crystal of the present invention are shown.

[0037] The raw material of Ga is, for example, Ga ２ O ３ As a raw material of the M element, for example, an oxide of the M element can be used. Specifically, when the M element is Al, Al ２ O ３ can be used, and when the M element is In, In ２ O ３ As the raw material of the additional element D, for example, an oxide or a fluoride of D can be used. Specifically, when D is Si, SiO ２ can be used. Here, SiO ２ The raw material may be in the form of a powder or a single crystal plate. The raw material may contain two or more of the elements exemplified above.

[0038] In one embodiment, the above-mentioned raw material is a compound of the general formula (Ga １－ｘ M ｘ ) ２ O ３ (0≦x<0.8). In the general formula, x may satisfy 0≦x≦0.5 or 0≦x<0.5. If necessary, a raw material mixture containing each raw material may be prepared.

[0039] <Step S120: Step of growing crystals from raw materials by hydrothermal synthesis in the presence of a mineralizer> In step S120, the raw materials prepared in step S110 (or a raw material mixture prepared by mixing the respective raw materials) are grown into crystals by hydrothermal synthesis in the presence of a mineralizer.

[0040] As the mineralizer, a mineralizer containing an alkali metal and / or an alkaline earth metal, an acid mineralizer, or a mixture of both can be used. The mineralizer containing an alkali metal and / or an alkaline earth metal is a compound containing an alkali metal and / or an alkaline earth metal, and for example, halides (fluorides, chlorides, bromides, iodides, etc.) and inorganic salts (carbonates, etc.) of alkali metals and / or alkaline earth metals can be used. Non-limiting examples of the mineralizer include KF, K ２ CO ３ , RbF, Rb ２ CO ３ , CsF, Cs ２ CO ３ , CaF ２ , CaCO ３ , SrF ２ , SrCO ３ , BaF ２ , BaCO ３ and the like, and it is preferable to select at least one from the group consisting of these compounds. The alkali metals and / or alkaline earth metals and / or halogen elements contained in the mineralizer can be contained in the finally obtained β-type gallium oxide crystals. Examples of acid mineralizers include, but are not limited to, hydrochloric acid, nitric acid, sulfuric acid, formic acid, phosphoric acid, etc. The elements contained in the acid mineralizer can be contained in the finally obtained β-type gallium oxide crystals.

[0041] The method for preparing the solution (reaction solution) used for crystal growth by hydrothermal synthesis is not particularly limited. For example, when the raw material mixture is prepared in the above-mentioned step S110, a solution of a mineralizer may be added to the raw material mixture, and further mixing may be performed as needed. Alternatively, a mineralizer (preferably in powder or tablet form) may be added to the raw material mixture, and further mixing may be performed as needed. Alternatively, the above-mentioned raw materials may be added to an aqueous solution of the mineralizer and appropriately mixed. Here, the concentration of the mineralizer in the finally prepared solution is preferably in the range of 1 M to 50 M, more preferably in the range of 3 M to 45 M, even more preferably in the range of 5 M to 40 M, and particularly preferably in the range of 7 M to 30 M. Within the above concentration range, the upper limit may be less than 30 M. In exemplary embodiments, the concentration of the mineralizer may range from 1M to less than 30M, from 1M to 25M, from 1M to 20M, from 1M to 15M, from 3M to 15M, or from 3M to 12M.

[0042] The crystal growth conditions (specifically, temperature conditions) for hydrothermal synthesis can be adjusted depending on the type of alkali metal and / or alkaline earth metal contained in the mineralizer used and the concentration of the mineralizer. Although a certain degree of care is required when handling a highly alkaline solution, the desired solution can be prepared by appropriately adjusting the concentration of the mineralizer. It is also preferable to select the type of mineralizer depending on the raw materials used and / or the types of constituent elements of the target crystal.

[0043] The conditions for crystal growth using hydrothermal synthesis are not particularly limited and can be set depending on the size of the hydrothermal synthesis vessel (reaction vessel) used, etc. In an exemplary embodiment, the temperature condition is preferably set in the range of 400°C to 800°C. This ensures the production of the desired crystals. If the temperature is below 400°C, the desired crystals may not be produced, and if the temperature is above 800°C, the temperature may exceed the heat-resistant temperature of the reaction vessel. The pressure condition is preferably set in the range of 25 MPa to 250 MPa. In this context, the pressure condition means that the maximum pressure achieved during crystal growth is within the above range. The pressure condition varies depending on the amount of water contained in the reaction vessel, the size of the ampoule (sealed vessel) containing the reaction solution, the temperature conditions, etc. In an exemplary embodiment, the maximum pressure may be set in the range of 30 MPa to 250 MPa, 50 MPa to 225 MPa, or 75 MPa to 200 MPa.

[0044] The hydrothermal synthesis time can be adjusted appropriately from the viewpoint of completing crystal growth depending on the type and amount of raw materials used. Two or more temperature conditions may be set within the above-mentioned temperature range to set a predetermined temperature profile. Such a temperature profile can be designed taking into consideration the viewpoints of further improving the homogeneity and stability of the solution, and more efficiently producing the target crystals. An example of a specific temperature profile will be shown in the examples below.

[0045] In the manufacturing method of the present invention, crystals are grown by hydrothermal synthesis from raw materials (or raw material mixture) at temperatures significantly lower than those of the conventional methods described above. For example, in the CZ method, a phenomenon occurs in which specific components evaporate from the interface of the melt during the crystal growth process (crystal growth process) due to the melting point of the target crystal (Ga ２ O ３In the case of hydrothermal synthesis, decomposition and evaporation are likely to occur, and such decomposition and evaporation may also occur in the grown crystal, which may result in defects in the grown crystal. However, the manufacturing method of the present invention is less likely to cause such decomposition and evaporation, and therefore it is possible to suppress defects that may occur in the grown crystal. Furthermore, in the case of hydrothermal synthesis, the obtained crystal is generally obtained with the most stable composition, and although there is a possibility that this composition may deviate slightly from the target composition, even if such a deviation occurs, it is considered that the difference from the target composition is very small and can be adjusted.

[0046] [Uses of Crystal] Next, uses of the β-type gallium oxide crystal of the present invention will be described.

[0047] The use of the β-type gallium oxide crystal of the present invention is not particularly limited, but it is suitable for use as a semiconductor material. In one embodiment, the β-type gallium oxide crystal of the present invention can be made into a substrate usable as a wafer for semiconductor manufacturing by cutting and polishing the bulk crystal into a plate-like body. Here, in producing the substrate, the bulk crystal is cut by any method to obtain a plate-like body having the desired shape and surface orientation, and then the plate-like body is heat-treated under predetermined atmosphere, temperature, and time conditions, and the surface may then be polished. By performing the above-mentioned heat treatment, it is expected that residual strain inevitably generated during the crystal manufacturing process will be reduced.

[0048] 1 is a schematic diagram showing an example of a Schottky barrier diode (SBD) according to an embodiment of the semiconductor device of the present invention. Note that the semiconductor device of the present invention is not limited to an SBD, and may be another semiconductor diode or another semiconductor device.

[0049] The SBD 100 shown in FIG. 1 includes a substrate 110 made of the above-described β-type gallium oxide crystal, an anode electrode 120, and a cathode electrode .

[0050] The anode electrode 120 is a Schottky electrode provided on one surface (the upper surface in FIG. 1 ) of the substrate 110 and electrically connected to the substrate 110 via a Schottky junction. Therefore, the anode electrode 120 is preferably made of a metal material having a work function greater than that of the substrate 110. Examples of such metal materials include platinum (Pt) and gold (Au). The anode electrode 120 may have a single-layer structure made of one type of metal material, or a layered structure in which multiple metal materials are stacked. In the latter case, the anode electrode 120 may be configured, for example, by providing a first layer made of a metal material suitable for Schottky junction with the substrate 110 and then providing a second layer made of another metal material on the surface of the first layer.

[0051] The cathode electrode 130 is an ohmic electrode provided on the other surface (the lower surface in FIG. 1 ) of the substrate 110 and electrically ohmic-contacted with the substrate 110. Therefore, the cathode electrode 130 is preferably made of a metal material having a work function smaller than that of the substrate 110. Furthermore, the cathode electrode 130 is preferably made of a metal material that reduces contact resistance with the substrate 110 by heat treatment after being formed on the substrate 110. Examples of such metal materials include titanium (Ti). Here, like the anode electrode 120 described above, the cathode electrode 130 may have a layered structure in which multiple metal materials are stacked. For example, the cathode electrode 130 may be configured by providing a first layer made of Ti suitable for ohmic contact with the substrate 110 and then providing a second layer made of gold (Au) on the surface of the first layer. The cathode electrode 130 may be provided over the entire other surface (lower surface) of the substrate 110, or may be provided over a portion of that surface.

[0052] 2 is a schematic diagram showing an example of a metal oxide semiconductor field effect transistor (MOSFET) according to an embodiment of the semiconductor device of the present invention. Note that the semiconductor device of the present invention is not limited to a MOSFET, and may be a metal insulator semiconductor field effect transistor (MISFET), another semiconductor switching element, or any other semiconductor device.

[0053] 2 is a MOSFET with a lateral structure, and includes a first n-type semiconductor layer 210, a second n-type semiconductor layer 212, a third n-type semiconductor layer 214, a gate insulating film 220, a gate electrode 230, a source electrode 240, a drain electrode 250, and a semi-insulating layer 260. A buffer layer (not shown) may be provided between the first n-type semiconductor layer 210 and the semi-insulating layer 260. Note that the configuration of the lateral MOSFET is not limited to this, and other configurations may also be employed.

[0054] The second n-type semiconductor layer 212 and the third n-type semiconductor layer 214 are preferably buried in the first n-type semiconductor layer 210. The carrier concentration of the second n-type semiconductor layer 212 and the third n-type semiconductor layer 214 is preferably higher than the carrier concentration of the first n-type semiconductor layer 210. That is, in the configuration shown in FIG. － The second n-type semiconductor layer 212 and the third n-type semiconductor layer 214 are n-type semiconductor layers. ＋ Here, second n-type semiconductor layer 212 and third n-type semiconductor layer 214 may be formed by ion implantation into predetermined regions on one surface (top surface in FIG. 2 ) of first n-type semiconductor layer 210.

[0055] As the first n-type semiconductor layer 210, for example, a layer made of β-type gallium oxide crystal containing Si, Sn, or the like as the aforementioned additional element D can be used. The first n-type semiconductor layer 210 may be formed by epitaxial growth using one surface (the upper surface in FIG. 2 ) of the semi-insulating layer 260 as a base. Here, as the semi-insulating layer 260, for example, a substrate made of β-type gallium oxide crystal containing Mg, Fe, or the like as the aforementioned additional element D can be used.

[0056] The gate insulating film 220 is, for example, SiO ２ , Al ２ O ３ , HfO ２ , La ２ O ３ , Ta ２ O ５, ZrO ２ A thin film made of an oxide such as the above can be used.

[0057] Known electrode materials can be used as the materials for the gate electrode 230, the source electrode 240, and the drain electrode 250. Examples of such electrode materials include metals such as Al, Mo, Co, Zr, Sn, Nb, Fe, Cr, Ta, Ti, Au, Pt, V, Mn, Ni, Cu, Hf, W, Ir, Zn, In, Pd, Nd, and Ag, or alloys thereof; conductive metal oxide films such as tin oxide, zinc oxide, indium oxide, indium tin oxide (ITO), and indium zinc oxide (IZO); and organic conductive compounds such as polyaniline, polythiophene, and polypyrrole. The gate electrode 230, the source electrode 240, and the drain electrode 250 may be formed by known methods such as vacuum deposition and sputtering.

[0058] FIG. 3 is a schematic diagram showing another example of a MOSFET according to an embodiment of the semiconductor device of the present invention.

[0059] MOSFET 300 shown in Fig. 3 differs from MOSFET 200 shown in Fig. 2 in that it is a vertical structure MOSFET. In the following, explanations of MOSFET 300 that are similar to MOSFET 200 will be omitted or simplified.

[0060] The MOSFET 300 includes a first n-type semiconductor layer 310 , a second n-type semiconductor layer 312 , a third n-type semiconductor layer 314 , a gate insulating film 320 , a gate electrode 330 , a source electrode 340 , and a drain electrode 350 .

[0061] The carrier concentration of the second n-type semiconductor layer 312 and the third n-type semiconductor layer 314 is preferably higher than the carrier concentration of the first n-type semiconductor layer 310. That is, in the configuration shown in FIG. － The second n-type semiconductor layer 312 and the third n-type semiconductor layer 314 are n-type semiconductor layers. ＋ It is preferable that the semiconductor layer is a silicon-based semiconductor layer.

[0062] A plurality of grooves are formed in the first n-type semiconductor layer 310 and the third n-type semiconductor layer 314, and the grooves penetrate the third n-type semiconductor layer 314 and have a depth that reaches a certain distance in the film thickness direction of the first n-type semiconductor layer 310. A gate electrode 330 is buried in the grooves via a gate insulating film 320. As described above, the configuration shown in FIG. 3 is a trench-type vertical structure, but the configuration of a vertical MOSFET is not limited to this, and other configurations can also be adopted.

[0063] The present invention will be explained in more detail below based on examples, but the present invention is not limited to these examples.

[0064] [Crystal Production] <Example 1> Commercially available β-Ga was used as a raw material. ２ O ３ (powder, manufactured by Furuuchi Chemical Co., Ltd.) was prepared. ２ O ３ The scale bar in the figure is 30 μm.

[0065] The above β-Ga ２ O ３ CsF (powder equivalent to a 10 M aqueous solution) as a mineralizer and pure water (0.7 mL) were placed in a silver ampoule (diameter 5 mm x length 10 cm) and sealed. The sealed ampoule was then placed in a reaction vessel containing pure water for hydrothermal synthesis. The hydrothermal synthesis conditions included a temperature profile in which the temperature was raised to 700°C over 12 hours, maintained at that temperature for 24 hours, and then lowered to 600°C over 100 hours to complete crystal growth. The maximum pressure reached during this period was 128 MPa. The temperature reduction program from 600°C to room temperature at the end of crystal growth was set to 1 hour, followed by natural cooling. This yielded the crystals of Example 1.

[0066] <Example 2> The hydrothermal synthesis conditions were a temperature profile in which the temperature was raised to 700°C over 12 hours, maintained at that temperature for 24 hours, and then lowered to 450°C over 250 hours to complete the crystal growth. The maximum pressure reached during this period was 137 MPa. The other conditions were the same as in Example 1, and the crystals of Example 2 were obtained.

[0067] <Example 3> The hydrothermal synthesis conditions were a temperature profile in which the temperature was raised to 650°C over 12 hours, maintained at that temperature for 24 hours, and then lowered to 550°C over 100 hours to terminate crystal growth. The maximum pressure reached during this period was 170 MPa. The other conditions were the same as in Example 1, and the crystals of Example 3 were obtained.

[0068] Example 4: Instead of CsF, RbF (powder in an amount equivalent to a 10 M aqueous solution) was used as the mineralizer, and the hydrothermal synthesis conditions were as follows: the temperature was raised to 730°C over 12 hours, maintained at that temperature for 24 hours, and then lowered to 430°C over 300 hours, completing the crystal growth. The maximum pressure reached during this period was 167 MPa. The other conditions were the same as in Example 1, and the crystals of Example 4 were obtained.

[0069] <Example 5> Instead of CsF as a mineralizer, KF (powder in an amount equivalent to a 10 M aqueous solution) was used, and the hydrothermal synthesis conditions were a temperature profile in which the temperature was raised to 730°C over 12 hours, maintained at that temperature for 24 hours, and then lowered to 430°C over 300 hours to terminate crystal growth. The maximum pressure reached during this period was 168 MPa. The other conditions were the same as in Example 1, and the crystals of Example 5 were obtained.

[0070] Table 2 shows the conditions for producing the crystals in Examples 1 to 5 described above.

[0071]

[0072] [Measurement and Evaluation] <Microscopic Observation> The crystals obtained in Examples 1 to 3 above were observed under an SEM. Fig. 5 shows an SEM image of the crystals of Example 1 as a representative example. The scale bar in the figure is 100 µm.

[0073] 5, it was confirmed that bulk crystals could be obtained by hydrothermal synthesis using the method of the present invention. Although not shown, bulk crystals were also confirmed in the SEM images of the crystals of Examples 2 and 3.

[0074] The crystals obtained in Examples 4 and 5 were observed under an optical microscope. Figures 6 and 7 show microscopic images of the crystals of Examples 4 and 5, respectively. The scale bars in the figures are 1 mm.

[0075] 6 and 7, it was confirmed that the crystals of Examples 4 and 5 were larger than the crystals of Examples 1 to 3 described above with reference to FIG.

[0076] <EDX Measurement> The elemental compositions of the crystals obtained in Examples 1 to 5 above were measured by energy dispersive X-ray spectroscopy using an EDX attached to the SEM used for the SEM observation described above.

[0077] As a representative example, Figure 8 shows the results obtained for the crystal of Example 1. Here, the crystal of Example 1 shows the measurement results for the bulk crystal (see Figure 5), and also shows the results for the raw material β-Ga ２ O ３ 8, the intensity on the vertical axis is a normalized value with the highest intensity value of each spectrum set to 1.0.

[0078] According to FIG. 8, the two EDX spectra mentioned above are almost completely consistent, and the obtained crystal is Ga ２ O ３ Although not shown, the crystals of Examples 2 to 5 also had the same composition as the crystal of Example 1. ２ O ３ It was confirmed that the composition was:

[0079] <X-ray Diffraction Measurement> Powder samples were prepared from the crystals obtained in Examples 1 to 5, and subjected to powder X-ray diffraction measurement. The results are shown in Figures 9 to 11.

[0080] The upper rows of Figures 9, 10 and 11 show the results obtained for the crystals of Examples 1, 4 and 5, respectively. ２ O ３ The bottom row shows the measurement results of β-Ga ２ O ３ The simulation results of the diffraction chart of (monoclinic system) are shown.

[0081] 9, it was found that the diffraction chart of the crystal of Example 1 had a very high degree of agreement with the diffraction chart obtained by the simulation in terms of peak position (angle 2θ) and intensity (normalized intensity). This indicates that the obtained crystal is a monoclinic β-Ga ２ O ３Although not shown, the crystals of Examples 2 and 3 were also found to have a monoclinic β-Ga phase, similar to the crystal of Example 1. ２ O ３ It was confirmed that the crystalline phase was

[0082] 10 and 11, similar to the crystals of Examples 1 to 3 described above with reference to FIG. 9, monoclinic β-Ga ２ O ３ It was confirmed that the crystalline phase was

[0083] <Secondary Ion Mass Spectrometry> The hydrogen (H), fluorine (F), and cesium (Cs) concentrations of the crystals of Example 1 were measured using a secondary ion mass spectrometer (IMS-6F, manufactured by Cameca) and a time-of-flight secondary ion mass spectrometer (TOF-SIMS, manufactured by IonTOF), respectively. The results are shown in FIG.

[0084] According to FIG. 12, the hydrogen concentration in the obtained crystal was about 5×10 at a depth of 3 μm. ２０ atoms / cm ３ is less than 1×10 ２２ atoms / cm ３ The following is satisfied, and the fluorine concentration is about 1×10 ２０ atoms / cm ３ is less than 1×10 ２１ atoms / cm ３ The following is satisfied, and the cesium concentration is approximately 1 × 10 at a depth of 3 μm. １７ atoms / cm ３ is less than 1×10 ２０ atoms / cm ３ It was found that the following was satisfied. It was also confirmed that the concentration ratio of gallium and oxygen was almost the same as the theoretical composition. Although not shown, the crystals of Examples 2 to 5 were also subjected to a similar component analysis, and the same results as those of the crystal of Example 1 were obtained.

[0085] As described above, the present invention can provide β-type gallium oxide crystals in which oxygen defects are suppressed and which are suitable for use as semiconductor materials for a variety of applications. The present invention can also provide a method for producing the above-described β-type gallium oxide crystals under milder conditions than conventional methods, particularly at lower temperatures. The present invention can also provide semiconductor materials and semiconductor devices that use the above-described β-type gallium oxide crystals.

[0086] 100 Schottky barrier diode (SBD) 110 β-type gallium oxide crystal substrate 120 anode electrode 130 cathode electrode 200 metal oxide semiconductor field effect transistor (MOSFET) 210 first n-type semiconductor layer 212 second n-type semiconductor layer 214 third n-type semiconductor layer 220 gate insulating film 230 gate electrode 240 source electrode 250 drain electrode 260 semi-insulating layer 300 metal oxide semiconductor field effect transistor (MOSFET) 310 first n-type semiconductor layer 312 second n-type semiconductor layer 314 third n-type semiconductor layer 320 gate insulating film 330 gate electrode 340 source electrode 350 drain electrode

Claims

1. Contains at least gallium (Ga), oxygen (O) and hydrogen (H), and is called β-Ga ２ O ３ β-type gallium oxide crystal having substantially the same crystal structure as the crystal.

2. The crystal composition is the general formula (Ga １－ｘ M ｘ ) ２ O ３－ｙ (wherein M is at least one element selected from the group consisting of aluminum (Al) and indium (In), and x and y each independently satisfy 0≦x<0.8 and −0.5≦y≦0.5.) 3. The concentration of hydrogen is 1 x 10 １６ atoms / cm ３ 1x10 or more ２３ atoms / cm ３ The crystal according to claim 1 or 2, which has the following range:

4. The crystal according to any one of claims 1 to 3, further containing at least one additional element D selected from the group consisting of silicon (Si), germanium (Ge), tin (Sn), iridium (Ir), magnesium (Mg), iron (Fe), copper (Cu), silver (Ag), zinc (Zn), and cadmium (Cd).

5. The crystal according to any one of claims 1 to 4, further containing an alkali metal and / or an alkaline earth metal.

6. The concentration of the alkali metal and / or alkaline earth metal is 1×10 １２ atoms / cm ３ 1x10 or more ２０ atoms / cm ３ The crystal according to claim 5, wherein the crystal has a molecular weight of 1000 or more and a molecular weight of 1000 or more.

7. The crystal according to any one of claims 1 to 6, further containing at least one halogen element selected from the group consisting of fluorine (F), chlorine (Cl), bromine (Br) and iodine (I).

8. The crystal according to claim 7, wherein the halogen element includes at least F.

9. The crystal according to claim 8, wherein the halogen element is F.

10. The concentration of the halogen element is 1 x 10 １６ atoms / cm ３ 1x10 or more ２３ atoms / cm ３ The crystal according to any one of claims 7 to 9, wherein the crystal has a molecular weight of 1000 or more and a molecular weight of 1500 or more.

11. A method for producing the crystals according to any one of claims 1 to 10, comprising growing crystals by hydrothermal synthesis from raw materials containing the elements to be contained in the crystals in the presence of a mineralizer containing an alkali metal and / or an alkaline earth metal, or an acid mineralizer, or a mixed mineralizer of both.

12. The method of claim 11, wherein the concentration of the mineralizer ranges from 1M to 50M.

13. The method according to claim 11 or 12, wherein in growing the crystal by hydrothermal synthesis, the temperature is in the range of 400°C or higher and 800°C or lower, and the maximum pressure is in the range of 25 MPa or higher and 250 MPa or lower.

14. A semiconductor material comprising the crystal according to any one of claims 1 to 10.

15. The semiconductor material according to claim 14, which is a plate-shaped substrate.

16. A semiconductor device comprising a layer of the semiconductor material according to claim 14 and / or the semiconductor material according to claim 15.

17. The semiconductor device according to claim 16, which is a diode or a switching element.

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