JP5510631B2 - Hexagonal wurtzite compound single crystal and method for producing the same - Google Patents

Description

  The present invention relates to a hexagonal wurtzite compound single crystal and a method for producing the same, and more particularly to a hexagonal wurtzite compound single crystal, a method for producing the same, and a single crystal substrate for epitaxial growth.

  In general, a hexagonal crystal has four crystal axes including three a axes forming 120 ° in a regular hexagonal plane and a c axis perpendicular to the a axis.

  1A to 1C are diagrams showing hexagonal crystals, FIG. 1A is a perspective view, FIG. 1B is a top view of FIG. 1A, and FIG. FIG. 2 is a front view of the m-plane in FIG. As shown in FIG. 1A, the (0001) plane perpendicular to the c-axis is called the c-plane, and the plane parallel to the c-axis and any a-axis is called the m-plane, as shown in FIG. In addition, a plane parallel to the c-axis and perpendicular to the arbitrary a-axis is called an a-plane. The a-plane and m-plane are planes perpendicular to the c-plane and parallel to the c-axis direction. Further, when the m-plane is viewed from the front, it becomes as shown in FIG. 1C, and the crystal lattice when the c-plane is viewed from the side can be seen.

  Among the hexagonal crystal systems, the crystal structure found in the compound represented by AX (A is a positive element, X is a negative element), that is, the atomic arrangement of the wurtzite structure is that the A atom and the X atom are hexagonal close-packed structures, respectively. The A atom has four X atoms coordinated in a regular tetrahedral shape, and the X atom has four A atoms coordinated in a tetrahedral shape.

  In each tetrahedral cluster, as shown in FIG. 1 (a), the direction parallel to the c-axis with X immediately above A is + c, and as shown in FIG. 1 (b), directly above X. The direction in which A is present is called -c, and the c-plane perpendicular to the c-axis and + c and -c directions are written as (0001) plane and (000-1) plane, respectively. When the c-plane is cut out, as shown in FIG. 1C, only the element A appears on the (0001) plane and only the element X appears on the (000-1) plane. The surface of the single crystal after growth is the same.

  In order to take such an atomic arrangement, the wurtzite structure has polarity in the c-axis direction. Compounds known to have a hexagonal wurtzite structure include wurtzite zinc sulfide (ZnS), zinc oxide (ZnO), aluminum nitride (AlN), gallium nitride (GaN), and nitride. Indium (InN) and the like can be given.

  Hexagonal wurtzite compound single crystal growth methods include vapor phase method, liquid phase method, and melt method, but the vapor phase method and melt method each have high defect density, very high pressure for growth, There are drawbacks such as requiring high temperatures. In contrast, the liquid phase method is characterized in that high-quality crystals with a low defect density can be obtained at a relatively low temperature. In particular, the solvothermal method is said to be suitable for high-quality crystal growth with low defects and impurity concentrations. The solvothermal method is a general term for a method of obtaining a single crystal by charging a raw material and a seed crystal in a container holding a supercritical solvent, and dissolving and reprecipitating the raw material using a temperature difference. When is water, it is called a hydrothermal method, and when it is ammonia, it is called an ammonothermal method.

  Hexagonal wurtzite-type compounds have already been put into practical use in recent years because of their direct transition type band gap, high electron mobility, and ability to continuously form materials with narrow band gaps to wide materials. Following GaN-based LEDs, development to ultraviolet and green LEDs, LDs, power devices, high-frequency devices and the like is expected.

  However, the negative element, which is one of the elements forming the hexagonal wurtzite crystal, is a molecular gas such as nitrogen or oxygen or a volatile element such as sulfur or selenium. It is difficult to maintain a stoichiometric ratio. For this reason, studies have been made to suppress the occurrence of defects in which negative elements are missing in the crystal by utilizing the fact that crystal growth is possible in an environment containing negative element components in a high-pressure vessel sealed by the solvothermal method. As a result, a certain degree of result was obtained. For example, the half-value width of the rocking curve of the (0002) plane in X-ray diffraction has been remarkably improved.

  Nevertheless, dislocation defect density, which is a large defect, deteriorates unexpectedly, and there is a problem that dislocations and cracks occur when heat and stress are applied, but it is not handled at all. Currently. A universal method for solving all the problems is to obtain a complete crystal having no defects at all, but it is not very difficult and practical based on the characteristics of the hexagonal wurtzite crystal described above.

  Hereinafter, among the compounds having a hexagonal wurtzite crystal structure, zinc oxide (hereinafter referred to as ZnO) single crystal, more specifically, blue-violet, ultraviolet light emitting element (substrate), surface acoustic wave (SAW), gas sensor, The description will focus on a ZnO single crystal that is used in various fields such as a piezoelectric element, a transparent conductor, and a varistor and exhibits an excellent function, and a substrate using the ZnO single crystal. However, the hexagonal wurtzite compound single crystal of the present invention is not limited to ZnO.

  Zinc oxide (ZnO) has a crystal structure of a hexagonal wurtzite compound, a direct transition has a large forbidden band of 3.37 eV, and an exciton binding energy (ZnO: 60 meV) is another compound semiconductor material. Is very large (GaN: 26 eV, ZnSe: 20 eV, etc.), and excitons are effective in the normal operating temperature range of the light emitting device. Therefore, zinc oxide-based materials (ZnO, ZnMgO, ZnCdO, ZnCuO, etc.) based on ZnO are expected as highly efficient light-emitting device materials. The exciton binding energy is very high, for example, heat generation when using a large current in a light-emitting device, and heat dissipation due to a large area is not good, and the light emission energy efficiency does not decrease even if the device temperature rises. It also has an important merit.

  On the other hand, ZnO has the same crystal structure as GaN and has a close lattice constant (lattice mismatch is about 2%), and can be manufactured at a much lower cost than GaN single crystals. It is also expected as a substrate for GaN thin film growth that replaces SiC.

In order to form a light emitting device of a zinc oxide-based material, a single crystal substrate for forming a thin film is required. Single crystal growth of zinc oxide has been studied for a long time, and includes the melt method, which is a solid phase growth method, the VPT method, which is a vapor phase growth method, and the hydrothermal method, which is a liquid phase growth method. From the viewpoint of crystal growth rate, equipment cost, etc., growth by hydrothermal growth, which is already widely known in the production of artificial quartz, has received the most attention and many studies have been conducted. For example, Non-Patent Documents 1 and 2 describe a basic technique of ZnO single crystal growth by a hydrothermal method, and according to the growth method, a ZnO sintered body is placed under a crystal growth container at a ZnO seed. Crystals are respectively placed on top of the growth vessel and then filled with a solvent of an alkaline aqueous solution consisting of KOH and LiOH. Further, in a state where hydrogen peroxide is added as an oxygen generator, the growth temperature in the growth vessel is 370 to 400 ° C. and the pressure is 700 to 1000 kg / cm ² . By operating so as to be higher by 10 to 15 ° C. than the temperature, a zinc oxide single crystal is grown on the seed crystal.

  A lot of research has been done based on this report. For example, since ZnO is prone to oxygen deficiency and the crystallinity in the 0002 direction is not sufficient, a new oxidizing agent has been proposed using a peroxidized raw material, and the half-value width of the 0002 plane of X-ray diffraction is 15 arcsec. A ZnO single crystal having high crystallinity is disclosed (see, for example, Patent Document 1). In addition, ZnO substrates formed by the hydrothermal method have already been experimentally sold in a size of about 1 cm square, and the half-value width of the 0002 plane in X-ray diffraction of these ZnO substrates is as good as 10 to 20 arcsec. The value is obtained (for example, refer nonpatent literature 3).

  However, the ZnO single crystals obtained by these conventional techniques have improved crystallinity observed by X-ray diffraction, but have a problem that they contain many dislocation defects. When dislocations exist in a single crystal substrate, when a thin film is formed on the substrate, it is transferred to the thin film, causing problems such as current leakage. In addition, when there are many dislocations, the dislocation grows when the temperature rises during operation as a device, causing problems such as loss of device function.

On the other hand, in the conventional ZnO single crystal growth by the hydrothermal method, it is common to use both KOH and LiOH as curing agents, so that a good crystalline ZnO single crystal grown in both the c-plane and m-plane directions can be obtained. can get. However, since the ionic radius of Li used here is very close to that of Zn, Li is taken into the grown ZnO single crystal. When trying to form a light-emitting device based on ZnO, Li moves through the crystal with heat or electric field, which obstructs ZnO p-type formation and destabilizes the electrical properties of the thin film. Has been pointed out. Therefore, Patent Document 2 discloses a technique using NH ₄ OH instead of Li, and Patent Document 3 moves Li containing a ZnO single crystal obtained by a hydrothermal method by heat treatment to the surface layer portion. A technique for etching the surface to reduce Li in the crystal is disclosed.

However, in Patent Document 2, although the Li content is significantly reduced, the crystallinity is greatly reduced. In Patent Document 3, although the crystallinity is good, Li is reduced only to about 10 ¹⁵ / cm ^3. Absent.

JP 2006-225213 A JP-A-6-279192 JP 2007-1787 A

"Hydrothermal synthesis of high-purity ZnO single crystals and evaluation of stoichiometrics" (Noboru Sakagami, February 1988, Bulletin of Akita National College of Technology No. 23) "Growth kinetics and morphology of hydrothermal ZnO single crystals" (Noboru Sakagami, Masanobu Wada, Journal of the Ceramic Society of Japan 82-8 1974) "Growth of 2 inch Bulk Crystal by Hydromethod" (Katsumi Maeda, Semicond, Sci. Technol. 20 No4 (April 2005) S49-54)

  The ZnO material is a material that is weak against stress, particularly thermal stress, as compared with a conventional device material. Therefore, for example, when a thin film is grown on a ZnO substrate, dislocations observed at the transmission electron microscope level occur when the substrate is pressed from the surroundings and the temperature is raised, and in some cases, the dislocation is observed with an optical microscope. Observable cracks occur. Not only during film formation, but also during wafer process steps and light emitting device operation, if the temperature rises with stress applied to the substrate, mechanical defects such as dislocations occur. Therefore, even when a substrate having few dislocations is used, dislocation occurs due to application of stress and heat, and there is a problem that the electronic function of ZnO exciton binding energy cannot be utilized.

  The present invention has been made in view of such a problem, and the object of the present invention is to form a film because the dislocation defects are extremely reduced, so there is little adverse effect on the thin film and it is resistant to thermal stress. It is another object of the present invention to provide a hexagonal wurtzite compound single crystal that hardly causes dislocation during device operation and a method for producing the same.

  Further, when the hexagonal wurtzite compound single crystal is a ZnO-based material, in addition, since the Li content is remarkably reduced, the adverse effect on the device due to Li can be avoided. It is to provide a hexagonal wurtzite type compound single crystal and a method for producing the same.

  In order to solve the above-mentioned problems, the present inventors have considered the stress dispersibility when subjected to thermal stress and the suppression of dislocation progress due to the stress, and as a result, unexpectedly pursued the conventional high crystallinity and non-domain. Contrary to the royal road of single crystal growth, the above problem is solved by forming an unprecedented fine structure having a fine domain structure of a hexagonal wurtzite compound single crystal while maintaining a crystallinity of a certain degree or more. It came to solve.

The present invention has been made to achieve such an object, and the invention according to claim 1 includes an a-axis forming 120 ° in a regular hexagonal plane, and a c-axis perpendicular to the a-axis. A hexagonal wurtzite compound single crystal having an island-shaped crystal microdomain having a crystal lattice arrangement different from the matrix region in a matrix region having a continuous and uniform crystal lattice, The c-axis in the crystal microdomain is parallel to the c-axis of the matrix region, and an arbitrary cross section of the wurtzite compound single crystal is observed with a transmission electron microscope at an observation magnification of 1.5 million, in a region of 70 nm × 40 nm. When 20 crystal lattice images are randomly observed, the crystal region having a size of 3 to 50 nm in which the matrix region and the crystal lattice have the same directionality but are discontinuous in the matrix region. Material domain is present, the ratio of the area of the crystal microdomains, average Ri Ah or 50% of the total observation point, the wurtzite type compound single crystal, selected ZnO, ZnMgO, ZnCdO, ZnCuO, ZnOS, from ZnOSe and wherein the der Rukoto.

  The invention according to claim 2 is the invention according to claim 1, wherein the size of the crystal microdomain is 3 to 50 nm, and the cross-sectional area of the crystal microdomain when observed in an arbitrary plane is The sum is 50% or more with respect to the cross-sectional area of the matrix region other than the crystal microdomain.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the half-value width of the rocking curve of the 0002 plane measured by the X-ray diffraction method is 25 arcsec or more and 250 arcsec or less. Features.

The invention according to claim 4 is the invention according to claim 1, 2 or 3, wherein the dislocation density observed with a transmission electron microscope is 1 × 10 ⁴ / cm ² or more, 9 × 10 ⁶ / It is characterized by being cm ² or less.

The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the Li concentration in the crystal is 1 × 10 ¹² / cm ³ or more and 9 × 10 ¹⁵ / cm ³ or less. It is characterized by being.

The invention according to claim 6 is characterized by comprising the hexagonal wurtzite compound single crystal according to any one of claims 1 to 5 .

  The hexagonal wurtzite compound single crystal of the present invention has a significantly reduced stress strain from the beginning, and is highly resistant to the thermal stress experienced by the substrate single crystal in the process from thin film growth to device operation. Thus, there is an effect that the characteristic expression of the hexagonal wurtzite type compound material that was originally canceled can be realized. At the same time, since the handling of the substrate is easy, there is an effect that the burden of device formation is reduced and the durability is excellent.

(A) thru | or (c) are figures which show a hexagonal system single crystal structure. It is a figure for demonstrating the crystal micro domain structure based on this invention. It is a block diagram for demonstrating the manufacturing apparatus of the hexagonal wurtzite type compound single crystal concerning this invention. It is process drawing for demonstrating Example 1 of the manufacturing method of the hexagonal wurtzite type compound single crystal based on this invention. It is process drawing for demonstrating Example 2 of the manufacturing method of the hexagonal wurtzite type compound single crystal based on this invention.

Embodiments of the present invention will be described below with reference to the drawings.
The hexagonal wurtzite type compound single crystal of the present invention is a single crystal of a compound having a hexagonal wurtzite type crystal structure, for example, nitrides such as GaN, AlN, InN, ZnO, ZnS, ZnSe, etc. The zinc compound can be mentioned. In addition, mixed crystals such as AlGaN and InGaN, and compounds doped with impurities such as ZnMgO, ZnCuO, and ZnOS as long as the hexagonal wurtzite crystal structure is maintained are also included. In the present invention, the hexagonal wurtzite type is not particularly limited, but in the case of ZnO-based materials such as ZnO, ZnMgO, ZnCuO, ZnOS, the improvement of thermal stress resistance, which is the greatest effect of the present invention, is improved. Remarkably expressed.

  The hexagonal wurtzite compound single crystal according to the present invention is characterized by having a crystalline microdomain structure.

  FIGS. 2A and 2B are diagrams for explaining a specific example of the crystal microdomain structure according to the present invention. FIG. 2A is a diagram illustrating an interface in the diagram shown in FIG. FIG. 2B is an enlarged view of the crystal microdomain structure shown in FIG. 2A, in which the enclosed island-like crystal microdomain structures are mixed. In the drawing, D indicates a region of a crystal microdomain structure, M indicates a matrix region, a indicates an arrangement of c planes in the matrix region, and b indicates an arrangement of c planes in the region of the crystal microdomain structure. Although the crystal microdomain structure D is shown in an elliptical shape, this is shown for convenience of explanation, and the actual crystal microdomain structure is not limited to an elliptical shape. .

  As shown in FIG. 2B, the crystal microdomain structure is a hexagonal crystal, but the crystal lattice plane a visible in the matrix region M and the crystal lattice in the region D of the crystal microdomain structure mixed in the matrix region M The surface b is in a discontinuous state shifted by “d”. However, the direction of the c-axis of the discontinuous crystal lattice plane is the same.

  That is, the hexagonal wurtzite compound single crystal according to the present invention is a hexagonal wurtzite compound single crystal having an a-axis forming 120 ° in a regular hexagonal plane and a c-axis perpendicular to the a-axis. A matrix region having a continuous and uniform crystal lattice includes an island-like crystal microdomain having a crystal lattice arrangement different from that of the matrix region, and the c-axis in the crystal microdomain is It has a crystalline microdomain structure that is parallel to the c-axis.

  Here, it has been described that the crystal microdomain structure is the same hexagonal crystal as that of the matrix region, but there are cases where the crystal microdomain structure can take not only a hexagonal crystal but also a tetragonal crystal.

  Such a microdomain structure includes a crystal lattice arrangement in which the c-axis is antiparallel to the crystal lattice arrangement in the matrix region, or an arrangement in which the a-axis is rotated by a predetermined angle around the c-axis. There are cases where you have.

  By having such a crystal microdomain structure, resistance to thermal stress is remarkably exhibited. In the hexagonal wurtzite compound single crystal of the present invention, having a crystal microdomain structure means that an arbitrary cross section of the hexagonal wurtzite compound single crystal is observed with a transmission electron microscope at a magnification of 1.5 million times, When 20 crystal lattice images are randomly observed in a region of 70 nm × 40 nm, the matrix region and the crystal lattice have the same directionality but are discontinuous in the matrix region in which the crystal lattice is continuous. A crystal microdomain having a size of ˜50 nm is present, and the ratio of the area of the crystal microdomain is 50% or more of the entire observation location on average. The cross section observed with a transmission electron microscope may be, for example, a cross section parallel to the c axis of a hexagonal wurtzite compound single crystal or a cross section parallel to the a axis.

  When the proportion of the area having the crystal microdomain structure is less than 50%, the thermal stress resistance that is the effect of the present invention is not exhibited. The crystal lattice is continuous means that the crystal lattice line observed by a transmission electron microscope is shifted or fluctuated within only half of the line width, and discontinuous means that the crystal lattice line is This refers to the case where they are not connected or are connected with a shift of more than half the crystal lattice line width. The shape of the crystal microdomain can take various shapes such as a circle, an ellipse, a triangle, a rectangle, and a rhombus.

  There is no particular limitation on the size of the crystal microdomain, but if the domain is too small, it will not exhibit thermal stress resistance because it resembles a conventional high crystallinity single crystal, and if it is too large, the stress dispersion effect will not appear. Therefore, the range of 3 to 50 nm is preferable, and the range of 5 to 30 nm is more preferable. The size of the crystal microdomain here refers to the maximum width (maximum diameter) of the domain.

  The hexagonal wurtzite compound single crystal in the present invention preferably has a half-value width of the rocking curve of the 0002 plane in the range of 20 arcsec to 250 arcsec as measured by the X-ray diffraction method. Conventionally, studies on hexagonal wurtzite compound single crystals have mainly focused on narrowing the full width at half maximum of high crystallinity, that is, rocking curves, and high crystallinity single crystals of less than 20 arcsec have been obtained. However, if the full width at half maximum of the rocking curve is less than 20 arcsec, the high crystallinity tends to lower the thermal stress resistance, which is not preferable.

  On the other hand, if it exceeds 250 arcsec, the thermal stress resistance is developed, but the crystalline microdomain approaches a polycrystalline body that exists randomly in various directions, so the crystallinity is too low and the original single crystal characteristics are developed. No longer. Therefore, the half width of the rocking curve of the 0002 surface needs to be in the range of 20 arcsec to 250 arcsec, preferably in the range of 25 to 200 arcsec, and more preferably in the range of 30 to 150 arcsec.

  The reason why the thermal stress resistance is remarkably improved by the crystal microdomain structure as described above is not necessarily clear at present, but it is a case of macro ceramic materials by having a micro microstructure while having single crystallinity. Similarly, it is estimated that there is an effect of improving the dispersibility of stress and suppressing the progress of stress dislocation (crack arrest). Conventionally, in the examination of a hexagonal wurtzite compound single crystal, high crystallinity has been pursued in both the corner and the corner as a substrate for thin film growth. However, the hexagonal wurtzite type is originally a crystal in which hexagonal wurtzite and cubic sphalerite are easy to mix. Therefore, it is difficult to be completely domainless. In the present invention, contrary to the conventional high-crystallinity and non-domain pursuit of single crystal growth, the ZnO single crystal has a fine domain structure while maintaining a crystallinity of a certain level or more. By forming the structure, practical crystallinity and thermal stress resistance were realized by the present invention.

The hexagonal wurtzite compound single crystal in the present invention preferably has a dislocation density of 1 × 10 ⁴ / cm ² or more and 9 × 10 ⁶ / cm ² or less observed with a transmission electron microscope. Since it has a crystalline microdomain structure, the thermal stress resistance is improved and the occurrence and development of dislocations due to thermal stress is prevented, and the inherent effect of the present invention is further enhanced by the absence of dislocations. Remarkably expressed.

When the dislocation density is measured with a transmission electron microscope, 20 crystal lattice images are randomly observed in a 7 μm × 8 μm region at a microscope observation magnification of 25000 times, and the number of dislocations is counted. The dislocations have various shapes such as a dot shape, a straight line shape, and a curved shape, but all shapes are formed without depending on the shape, and the total is defined as the number of dislocations. If the dislocation density is too high, the dislocation is inherited by the thin film formed on the substrate and the film characteristics are deteriorated. Therefore, the dislocation density is preferably 9 × 10 ⁶ / cm ² or less, more preferably 5 × 10 ⁶ / cm. ² or less, more preferably 1 × 10 ⁶ / cm ² or less. The lower the dislocation density, the better. However, 1 × 10 ⁴ / cm ² is the lower limit obtained in the present invention. In a single crystal having high crystallinity that has been pursued in the past, although the crystallinity is very high, the dislocation density is about 9 × 10 ⁷ / cm ² , and a large number of dislocations are inherent. For the first time, a single crystal having a significantly reduced dislocation density of 9 × 10 ⁶ / cm ² or less was realized.

In the hexagonal wurtzite compound single crystal of the present invention, the Li concentration in the crystal is preferably 1 × 10 ¹² / cm ³ or more and 9 × 10 ¹⁵ / cm ³ or less. Conventionally, when Li is contained in a hexagonal wurtzite compound single crystal, particularly a single crystal of a ZnO-based material, Li moves in the crystal by heat or an electric field, which inhibits the p-type formation of ZnO. Deterioration of electrical characteristics has been regarded as a problem, and studies on reducing Li have been made. However, since the conventional hexagonal wurtzite compound single crystal has many dislocations and low thermal stress resistance, the truth of the effect of reducing Li was unknown.

However, since the single crystal in the present invention originally has few dislocations and is excellent in thermal stress resistance, for example, in the case of a material containing Zn and O, p-type inhibition is suppressed by reducing Li and the stability of electrical characteristics. It becomes possible to improve. Li needs to be at least two orders of magnitude lower than the concentration of 10 ¹⁷ to 10 ¹⁹ / cm ³ that is usually doped in the thin film, and is preferably 9 × 10 ¹⁵ / cm ³ or less, more preferably 5 × 10 ¹⁴ / cm ^3. cm ³ or less, more preferably 1 × 10 ¹⁴ / cm ³ or less. The lower the Li concentration, the better. However, 1 × 10 ¹² / cm ³ is the lower limit obtained in the present invention. In a single crystal having high crystallinity that has been pursued in the past, although the crystallinity is very high, the Li concentration is about 10 ¹⁶ to 10 ¹⁸ / cm ^3, which is very large. A single crystal having a significantly reduced Li concentration of 9 × 10 ¹⁵ / cm ³ or less was realized.

  The hexagonal wurtzite compound single crystal in the present invention preferably has the following characteristics in photoluminescence when a He—Cd laser is used as an excitation light source and irradiated with light having a wavelength of 325.0 nm. First, in photoluminescence at room temperature, the intensity (Igr) of a broad green band having a peak from 420 nm to 800 nm with respect to the intensity (Ibr) of a band edge having a peak near 380 nm is 0.1 or less. Preferably, it is 0.07 or less, more preferably 0.5 or less. Further, in the photoluminescence at 10K, it is preferable that the intensity (Igl) of the broad green band having a peak from 420 nm to 800 nm with respect to the intensity of the band edge emission having a peak near 380 nm (Ibl) is 1% or less, More preferably, it is 0.5% or less, More preferably, it is 0.1% or less. Further, the band edge emission intensity (Ibr) at room temperature with respect to the band edge emission intensity (Ibl) at 10K is preferably 2% or more, more preferably 3% or more, and further preferably 4% or more.

  In a hexagonal wurtzite compound single crystal, for example, in the case of ZnO, many levels are formed between bands due to oxygen defects, the presence of excess Zn, and the presence of various impurities. Green band light emission appears. They can be comprehensively evaluated by measuring photoluminescence at room temperature and a low temperature of about 10K. A low green band emission intensity relative to a band edge emission intensity at both room temperature and low temperature indicates that there are few unnecessary levels formed between the bands. Particularly, when the green band emission intensity is remarkably reduced when measured at a low temperature, it indicates that there are essentially few defects and impurities. On the other hand, when the band edge emission intensity at room temperature with respect to the band edge emission intensity at low temperature is above a certain level, the occurrence of defects due to temperature rise is reduced.

  Next, a preferable example of the method for producing a hexagonal wurtzite compound single crystal having a crystal microdomain structure of the present invention will be described in the case of a ZnO single crystal.

The method for producing a hexagonal wurtzite compound single crystal according to the present invention is based on the basic technique of ZnO single crystal growth by hydrothermal method described in Non-Patent Documents 1 and 2. That is, a ZnO raw material is placed at the bottom of the crystal growth vessel, and a ZnO seed crystal cut out parallel to the (0001) plane is placed at the top of the growth vessel, and then filled with an alkaline aqueous solvent composed of KOH, LiOH, and the like. . Further, in a state where hydrogen peroxide is added as an oxygen generator, the growth temperature in the growth vessel is 370 to 400 ° C. and the pressure is 700 to 1000 kg / cm ² . By operating so as to be higher than the temperature by a certain range, a zinc oxide single crystal is grown on the seed crystal.

Here, the following points can be mentioned as different production conditions in the present invention which are not disclosed in the basic technology.
1) The ZnO raw material is mainly crystal grains.
2) The temperature rising rate at the start of crystal growth is 0.5 ° C./min or more and 2 ° C./min or less, and the temperature difference between the upper part and the lower part in the growth container at the time of growth is 3 to 7 ° C. Be.
3) The cooling rate at the end of crystal growth is 0.5 ° C./min or more and 2 ° C./min or less.
4) Using a seed crystal obtained by slicing a single crystal grown in both the m-direction and the c-direction using both LiOH and KOH in parallel to the c-plane, in an + c direction and -c direction under an alkaline solution not containing LiOH It must be a two-stage method that grows

  The ZnO raw material used for the production of the hexagonal wurtzite compound single crystal of the present invention is preferably mainly crystal grains, and the crystal grains are more preferably those obtained by natural nucleation by a hydrothermal method. Further, it is preferable to produce the mineralizer without using a Li-containing compound such as LiOH as a mineralizer. Mainly crystal grains means that 50% or more of the ZnO raw material is crystal grains. The proportion of crystal grains is not particularly limited as long as it is 50% or more, and all may be crystal grains. When the raw material is a crystal grain, the dissolution rate in the alkaline aqueous solution becomes slow, and the concentration of the dissolved species in the alkaline solution decreases. It is presumed that this contributes to the formation of the crystalline microdomain structure in combination with the temperature increase rate effect of the postoperative.

  The size of the crystal grains is not particularly limited, but if it is too small, the specific surface area becomes large and the dissolution rate increases, and if it is too large, the necessary dissolved species concentration cannot be obtained. Therefore, it is preferably in the range of 0.1 mm to 10 mm, more preferably in the range of 0.5 mm to 7 mm, and still more preferably in the range of 1 mm to 5 mm. In order to control the dissolution rate of the ZnO raw material and the concentration of dissolved species in the aqueous solution so as to facilitate the formation of the crystal microdomain structure, it is also preferable to mix and use crystal grains having different sizes.

  The reason why the crystal grains obtained by the hydrothermal method are preferable for the formation of the crystal microdomain structure of the present invention is not clear at present. However, for example, the bulk density is higher than the crystal grains obtained by the vapor phase method, and oxygen defects are few, so the effect of slowing the dissolution rate in alkaline aqueous solution and the concentration of dissolved species in alkaline solution are reduced. It is estimated that it has the effect of

  In order to produce the crystal microdomain effect of the present invention more effectively, a single crystal not containing Li is manufactured. Therefore, in order not to contain Li in the crystal grains as a raw material, the crystal is grown Li-free. It is more preferable that

  In the production of the hexagonal wurtzite compound single crystal of the present invention, the rate of temperature rise at the start of crystal growth is not less than 0.5 ° C./min and not more than 2 ° C./min. The temperature difference between the upper part and the lower part is preferably in the range of 3 to 7 ° C. For crystal growth under hydrothermal supercriticality, the temperature difference between the lower part (raw material part) and the upper part (crystal growth part) in the growth vessel is important. If the temperature difference is large, the degree of supersaturation of the solution at the crystal growth portion becomes high, so that the potential barrier for precipitation of the dissolved species becomes low and precipitation occurs easily. Therefore, the size of the dissolved species that can exist in the solution is small, that is, the dissolved species having a low degree of polymerization (= low molecule) occupy the main body, and multi-angle growth is likely to occur. Since the precipitated molecules are small molecules, they easily move to an energetically stable place and are arranged in an orderly manner, resulting in improved crystallinity.

  On the other hand, when the temperature difference is small, the degree of supersaturation of the solution at the crystal growth portion becomes very low, so that low molecules cannot be precipitated and medium molecules of a certain degree or more are precipitated. When medium molecules try to bond with each other, the degree of freedom is low, so movement after precipitation is difficult, and alignment is difficult. Thus, when the temperature difference is low, a crystalline microdomain structure is easily formed. Therefore, conventionally, the temperature difference is about 10 to 15 ° C, but in the present invention, the temperature difference is preferably in the range of 3 to 7 ° C, more preferably 4 to 6 ° C. However, not only reducing the temperature difference during the growth, but also increasing the temperature rising rate at the start of crystal growth to 0.5 ° C./min to 2 ° C./min. It is important that it is 0.5 ° C./min or more and 2 ° C./min or less.

  Single crystal growth by hydrothermal has a long growth period of several months, and in terms of the whole process, the temperature rising period and the temperature falling period are less than 1 day, so it is considered that the influence is considered to be small and attention is paid. There wasn't. Surprisingly, however, in the present invention in which crystal grains are used as raw materials and the temperature difference during growth is very small, the present invention reveals for the first time that the rate of temperature increase and the rate of temperature decrease is very important. It was.

  At present, the mechanism for enabling the hexagonal wurtzite compound single crystal having the crystal microdomain structure of the present invention to have a temperature rising rate and a temperature decreasing rate is not necessarily clear. The temperature difference between the surface and the inside of the crystal causes a fine crack in the crystal grains and the alkali solution enters the inside, so that the dissolution rate is increased, and many nucleation occurs on the seed crystal surface during the temperature rising process. Phenomenon such as end.

  On the other hand, if the rate of temperature decrease is high, a temperature difference will occur between the surface of the grown single crystal and the inside, and dislocations and cracks will occur at the time of temperature decrease despite the formation of crystal microdomains and stable crystals. It becomes easy. Therefore, the rate of temperature rise and the rate of temperature fall are preferably 2 ° C./min or less, more preferably 1.5 ° C./min or less, and further preferably 1 ° C./min or less. If both speeds are too long, there is no adverse effect on the crystal characteristics, but if it is longer than necessary, the process becomes too long, so 0.5 ° C./min or more is preferable.

  In the production of a hexagonal wurtzite compound single crystal in the present invention, a seed crystal obtained by slicing a single crystal grown in both the m direction and the c direction using both LiOH and KOH in parallel to the c plane is used. It is preferable to use a two-stage method in which growth is performed in the + c direction and the −c direction under an alkaline solution not containing LiOH. Conventionally, it is known that LiOH grows well in both m and c directions, and KOH grows preferentially in the c direction. For this reason, it has become possible to obtain a single crystal containing no Li which adversely affects the control of thin film characteristics and device characteristics by the above-described two-stage method.

In the production of the hexagonal wurtzite compound single crystal in the present invention, the addition and addition amount of the oxygen generator, the raw material temperature, the growth temperature, and the growth pressure are not particularly limited, and the ZnO single crystal by the conventional hydrothermal method is used. Appropriate conditions are selected within the scope of basic technology (oxygen generator hydrogen peroxide, temperature in the growth vessel: 370 to 400 ° C., pressure: 700 to 1000 kg / cm ² ), and the filling rate in the vessel to give it is selected. . Among them, preferable conditions are that the growth temperature is 380 to 390 ° C., the growth pressure is 1100 to 1200 kg / cm ^2, and the growth is preferably performed in a relatively high temperature and high pressure region.

  In the production of a hexagonal wurtzite compound single crystal according to the present invention, an oxygen generator other than hydrogen peroxide is added, a doping element raw material is added to obtain a doped single crystal, a ZnO mixed crystal The addition of the corresponding raw material in the case of obtaining is not limited, and is appropriately performed according to the characteristics of the crystal to be obtained.

  In the production of the hexagonal wurtzite compound single crystal in the present invention, a seed crystal is used, but the surface of the seed crystal is preferably polished, and the RMS value in AFM measurement is preferably 0.2 or less. Conventionally, in single crystal growth by hydrothermal method, the seed crystal surface is partially dissolved and a smooth clean surface is formed until the temperature difference between the upper and lower sides is stabilized through the temperature rising process, so the seed crystal is only cut. Alternatively, some chemical etching may be applied, and smoothness as the seed crystal is transparent has been considered unnecessary.

However, in the present invention where the temperature difference between the upper and lower temperatures during growth is low and the rate of temperature rise is slow, the conditions are such that surface dissolution is suppressed as much as possible during the temperature rise process. Therefore, it is preferable that the surface of the seed crystal is polished smoothly. Further, the dislocation density of the seed crystal is preferably 9 × 10 ⁶ / cm ² or less. Conventionally, little attention has been paid to crystallinity of seed crystals and intrinsic dislocations. However, the dislocations inherent in the seed crystal are inherited by the single crystal that is hydrothermally grown thereon. Therefore, unlike the conventional case, in the production method of the present invention in which a single crystal having a greatly reduced dislocation density is obtained, it is more preferable that there are few dislocations in the seed crystal.

Specific examples of the present invention will be described below.
FIG. 3 is a configuration diagram for explaining an apparatus for producing a hexagonal wurtzite compound single crystal according to the present invention. FIG. 3A is a configuration diagram of a zinc oxide single crystal growth apparatus, and FIG. 3B is a configuration diagram of a zinc oxide single crystal growth vessel used in the zinc oxide single crystal growth apparatus. In FIG. 3 (a), a zinc oxide single crystal growing apparatus 11 is provided with heaters 21 and 22 in order to control the temperature condition of the high pressure autoclave 12 which can be set to a supercritical condition along the growing process in the present invention. Thus, the entire apparatus is shut off from the outside by a heat insulating material 23 for keeping the temperature condition constant.

  The autoclave 12 is a pressure-resistant container, and a zinc oxide single crystal growing container 31 is set in the autoclave housing portion 13, and the opening is closed by the lid 16 to seal the inside. The lid body 16 includes a packing member 15, and the autoclave main body 14 and the lid body 16 are firmly fastened by screws 17 to maintain a sealed state under high pressure. The upper part and the lower part of the outer periphery of the autoclave 12 are kept under a constant temperature condition by the heaters 21 and 22 arranged above and below.

  As shown in FIG. 3B, the zinc oxide single crystal growth vessel 31 is formed of a material that does not elute impurities under the internal reaction conditions, such as platinum (Pt) or gold (Au), and the inside is set with a seed crystal. The two regions are divided by an internal baffle plate 34, and the circulation of the solvent is controlled by a large number of holes provided in the internal baffle plate 34. The

  Similarly, seed crystals 41a to 41d are suspended and set inside the zinc oxide single crystal growth vessel 31 by a suspension composed of a frame 32 and a support 33 formed of platinum or the like so as not to elute impurities. A lid 37 for sealing the zinc oxide single crystal growth vessel 31 is set on the upper end of the zinc oxide single crystal growth vessel 31 after setting a starting material 51 such as a sintered body of zinc oxide powder or zinc oxide crystal grains. The lid 37 is provided with a minute opening 38 for injecting a solvent, an oxidizing agent, or the like. Further, a baffle ring 35 having a circulation hole is similarly provided on the outer periphery of the zinc oxide single crystal growth vessel 31, and the zinc oxide single crystal growth vessel 31 is supported in the autoclave housing portion 13.

Various measurement methods used in the present invention are as follows.
[Polishing method of single crystal substrate]
The as-cut substrate after single crystal growth and cutting is roughly polished with SiC polishing paper. The rough polishing is performed while supplying water using # 500, # 1200, and # 2400 in the order of Marumoto Struers polishing paper. Then, it grind | polishes using 3 micrometers, 1 micrometer, and 1/4 micrometer of Marumoto Struers diamond polishing powder in order, and it observes with an optical microscope by 200 time, and makes it a state without a crack. Next, CMP is performed using colloidal silica for CMP (manufactured by Marumoto Struers). The polishing plate rotation speed during polishing is 150 rpm.

[X-ray diffraction]
Using a Rigaku X-ray diffractometer (ATX-G), the tube target is measured at Cu (incident X-ray wavelength 1.54059 mm (Cu Kα1), tube voltage 50 kV, tube current 300 mA. (440) × 4 crystal The measurement of the rocking curve of the (0002) plane of ZnO is performed by measuring the scan axis ω axis (2θ = 34.430 ° fixed), continuous scan mode, step width 0.0001 °, scan speed 0. Perform at 02 ° / min.

[TEM observation]
(Observation of crystal lattice image)
An observation section is prepared by ion milling with Ar gas using an ion milling device (Gatan: 600 type). For TEM observation, an H-9000NAR manufactured by HITACHI is used, and an observation voltage of 300 nm and an imaging magnification of 300,000 times and a magnification of 5 million are used to shoot a visual field size of 70 nm × 40 nm. The determination of the crystal microdomain structure is performed using a photograph obtained by enlarging a photographed image 5 times only in the 0001 direction.

(Observation of dislocation)
An observation section is prepared by ion milling with Ar gas using an ion milling device (Gatan: 600 type). For TEM observation, an H-9000NAR manufactured by HITACHI is used, and a field size of 7 μm × 8 μm is photographed at an accelerating voltage of 300 kV, an imaging magnification of 5000 times, and an enlargement magnification (5 times) at an observation magnification of 25000 times.

[SIMS measurement]
The sample subjected to the conductive film coating treatment is measured by a sector type SIMS manufactured by CAMECA. At the time of positive ion measurement, the apparatus uses IMS-6F manufactured by CAMECA, irradiation source O ²⁺ , acceleration voltage 5.5 kV, raster region 150 μm × 150 μm, analysis region 60 μmφ, and secondary ion polarity by Positive and E-gun. Measure while charging compensation. When measuring negative ions, IMS-4F manufactured by CAMECA is used, and irradiation source Cs ⁺ , acceleration voltage 14.5 kV, raster region 125 μm × 125 μm, analysis region 30 μmφ, and secondary ion polarity are measured negatively. The content is determined by cutting about 5 μm while measuring from the vicinity of the surface and the detected value becomes almost constant. The quantification is performed using a standard sample (ZnO) containing a target element having a known concentration.

[Etch pit density]
A sample polished for analysis is used and evaluated using a Zn surface. The sample is immersed in a 10 wt% HCl solution prepared in advance for 3 minutes, thoroughly washed with pure water and dried, and then the Zn surface is observed with an optical microscope. The observation area is 5 × 5 mm and observation is performed at a magnification of 200 times, and the number of hexagonal etch pits is counted.

[PL measurement]
A He—Cd laser is used as an excitation light source, and light emission (photoluminescence) upon irradiation with light having a wavelength of 325.0 nm is detected. The measurement is performed at room temperature and low temperature (10K). As for emission, band edge emission having a peak in the vicinity of 380 nm, and broad green band emission having a peak from 420 nm to 800 nm are observed. The spectrum is measured at room temperature and low temperature, and the emission intensity of each peak is measured and evaluated.

  FIG. 4 is a process diagram for explaining Example 1 of the method for producing a hexagonal wurtzite compound single crystal according to the present invention. The manufacturing method of the hexagonal wurtzite compound single crystal of Example 1 was first made by using a sintered body of zinc oxide powder by a hydrothermal method, taking into consideration the temperature increase rate and the temperature decrease rate. The first step (S11) of pulverizing the aggregate of crystals to form crystal grains, and then using a hydrothermal method, a sintered body of zinc oxide powder and a seed crystal of zinc oxide single crystal are used to raise the temperature. A second step (S12) of forming a plate seed crystal after forming a ZnO bulk single crystal in consideration of the speed and the temperature lowering rate, and then the crystal grains formed in the first step, A ZnO bulk single crystal having a crystalline microdomain structure is obtained using the plate-like seed crystal formed in the step 2, using potassium hydroxide and lithium hydroxide as an alkaline solution, and taking into consideration the rate of temperature increase and the rate of temperature decrease. A third step (S13) of forming a single crystal substrate after the formation. .

Below, each process is demonstrated concretely.
[Hydrothermic crystal grain formation process]
The lower part (raw material part) of the platinum-made growth vessel is filled with 190 parts of a sintered body having a particle size of 3 mm to 10 mm obtained from high-purity zinc oxide powder manufactured by High-Purity Science Co., and platinum is placed on the upper part through a baffle plate. A mesh made was placed and 203 parts of a 4 mol / L aqueous potassium hydroxide solution was injected. Next, 0.5 part of hydrogen peroxide was injected as an oxidizing agent while suppressing the reaction between hydrogen peroxide and alkali, and the growth vessel was sealed.

  Next, the growth vessel is placed in an alloy autoclave, 57 parts of distilled water is added between the growth vessel and the autoclave, the autoclave is sealed, and heated at a heating rate of 5 ° C./min. The temperature was raised from 392 ° C. to 394 ° C. and maintained for 20 days, and then returned to normal pressure and room temperature at a temperature drop rate of 5 ° C./min to obtain an aggregate of Li-free amorphous microcrystals. The obtained aggregate was pulverized to obtain crystal grains having a particle size of 0.1 mm to 10 mm.

[Seed crystal formation process by hydrothermal method]
The lower part (raw material part) of the platinum growth vessel is filled with 190 parts of a sintered body having a particle size of 3 mm to 10 mm obtained from high-purity zinc oxide powder manufactured by High-Purity Science Co., Ltd. A plate-like piece having a (0001) plane perpendicular to the c-axis of a zinc oxide single crystal as a seed crystal is suspended, and 201 parts of an alkaline solution having a potassium hydroxide aqueous solution concentration of 3.5 mol / L and a lithium hydroxide concentration of 1.5 mol / L. Injected. Next, 0.7 part of hydrogen peroxide was injected as an oxidizing agent while suppressing the reaction between hydrogen peroxide and alkali, and the growth vessel was sealed.

  Next, the growth vessel is put in an alloy autoclave, 61 parts of distilled water is put between the growth vessel and the autoclave, and then the autoclave is sealed and heated at a temperature rising rate of 5 ° C./min. The temperature of the upper part was raised to 373 ° C. and then maintained for 36 days, and returned to normal pressure and normal temperature at a temperature drop rate of 5 ° C./min to obtain a ZnO bulk single crystal grown in both the c-axis and m-axis directions. This single crystal was cut into a plate with a thickness of 0.8 to 1.5 mm perpendicular to the c-axis, washed with alkali, and subjected to surface polishing to obtain a (0001) plane plate seed crystal.

[Single crystal growth process]
The lower part (raw material part) of the platinum growth vessel is filled with 200 parts of crystal grains having a particle size of 0.1 mm to 10 mm obtained by the hydrothermal method, and the upper part thereof is a seed crystal through a baffle plate. A plate seed crystal having a (0001) plane perpendicular to the c-axis prepared in advance by a hydrothermal method is suspended, and 201 parts of an alkaline solution having a potassium hydroxide aqueous solution concentration of 3.5 mol / L and a lithium hydroxide concentration of 1.5 mol / L. Injected. Next, 0.7 part of hydrogen peroxide was injected as an oxidizing agent while suppressing the reaction between hydrogen peroxide and alkali, and the growth vessel was sealed.

  Next, the growth vessel is placed in an alloy autoclave, 61 parts of distilled water is added between the growth vessel and the autoclave, and then the autoclave is sealed and heated at a heating rate of 3 ° C./min. The temperature of the upper part was raised to 383 ° C., then maintained for 36 days, and returned to normal pressure and normal temperature at a temperature drop rate of 3 ° C./min to obtain a ZnO bulk single crystal grown in both the c-axis and m-axis directions. This single crystal was cut into a plate shape having a thickness of 0.8 to 1.5 mm perpendicular to the c-axis and polished to obtain a (0001) plane single crystal substrate. The growing autoclave internal force was 1190 atm.

  Table 1 shows the results of the characteristics evaluation of the obtained substrate.

FIG. 5 is a process diagram for explaining Example 2 of the method for producing a hexagonal wurtzite compound single crystal according to the present invention.
The crystal grain formation step and seed crystal formation step by the hydrothermal method are the same as those in the first embodiment. That is, first, by using a sintered body of zinc oxide powder by a hydrothermal method, an aggregate of microcrystals formed in consideration of a temperature increase rate and a temperature decrease rate is pulverized to form crystal grains. Step (S21), and then, using a hydrothermal method, ZnO having a crystalline microdomain structure in consideration of the temperature increase rate and the temperature decrease rate, using a sintered body of zinc oxide powder and a seed crystal of zinc oxide single crystal A second step (S22) of forming a plate seed crystal after forming the bulk single crystal.

  Next, in Example 2, unlike Example 1 described above, the crystal grains formed in the first step and the plate seed crystals formed in the second step are used, and water is used as an alkaline solution. A third step (S23) of forming a single crystal substrate after forming a ZnO bulk single crystal using potassium oxide in consideration of the rate of temperature rise and the rate of temperature fall is included.

  In the above-described third step (S23), Example 1 and Example 1 except that 250 parts of 4.0 mol / L potassium hydroxide solution was injected as an alkaline solution into the lower part (raw material part) of the platinum growth vessel. Similarly, a ZnO bulk single crystal was obtained. This single crystal was cut into a plate shape having a thickness of 0.8 to 1.5 mm perpendicular to the c-axis and polished to obtain a (0001) plane single crystal substrate. The growing autoclave internal force was 1183 atm.

  Table 1 shows the results of the characteristics evaluation of the obtained substrate.

  A single-crystal ZnO thin film was grown on the single-crystal substrates obtained in Examples 1 and 2 under the following conditions using a molecular beam epitaxy apparatus. First, a single crystal substrate was placed and fixed on an Inconel substrate holder so that the -c surface was the surface, and introduced into a molecular beam epitaxy apparatus.

  This was heated in vacuum until the substrate temperature reached 800 ° C. and maintained in this state for about 10 seconds to obtain a clean substrate surface. Whether or not a desired clean surface has been obtained can be confirmed by the reflection high-energy electron diffraction pattern becoming streaky during the heat treatment.

Next, the temperature was lowered until the substrate temperature reached 500 ° C., and zinc and oxygen were supplied to grow a ZnO thin film. As typical growth conditions, the molecular beam equivalent pressure of zinc is 1.5 × 10 ⁻⁷ Torr, oxygen is activated through an RF plasma source, and then radical oxygen is 4.2 × 10 ⁻⁶ Torr. Supplied to. The film thickness of the grown film was measured by measuring the level difference from the masked part at the time of growth, and in this example, a 4000O ZnO thin film was grown by growth for 2 hours.

Whether or not the grown film has good crystallinity can be roughly determined by whether or not the reflected high-energy electron diffraction pattern after growth becomes streak-like, but by observing a cross-sectional TEM It can be confirmed. Also in this example, as a result of observing the cross-sectional TEM, no dislocation is observed in the grown film, and the dislocation density is at least 6 × 10 ⁻⁷ cm ⁻² or less, which is useful as a substrate for epitaxial growth. It was confirmed.

(Comparative Example 1)
The ZnO bulk single crystal and the (0001) plane single crystal substrate were formed in the same manner as in Example 1 except that the temperature during the single crystal growth was 383 ° C. for the lower portion of the growth vessel and 373 ° C. for the upper portion. Obtained. Table 1 shows the results of the characteristics evaluation of the obtained substrate.

(Comparative Example 2)
A ZnO bulk single crystal and a (0001) plane single crystal substrate were obtained in the same manner as in Example 1 except that the rate of temperature increase during the single crystal growth was 8 ° C./min. Table 1 shows the results of the characteristics evaluation of the obtained substrate.

(Comparative Example 3)
As a raw material used for single crystal growth, a ZnO bulk single crystal was used in the same manner as in Example 1 except that a sintered body having a particle size of 3 mm to 10 mm obtained from a high-purity zinc oxide powder manufactured by High-Purity Science Co., Ltd. was used. A 0001) plane single crystal substrate was obtained. Table 1 shows the results of the characteristics evaluation of the obtained substrate.

(Comparative Example 4)
A commercially available (Company A) ZnO single crystal substrate was purchased and evaluated. The results are shown in Table 1.

(Comparative Example 5)
A commercially available (Company B) ZnO single crystal substrate was purchased and evaluated. The results are shown in Table 1.

  INDUSTRIAL APPLICABILITY The present invention can provide a hexagonal wurtzite compound single crystal having extremely reduced dislocation defects and being resistant to thermal stress, and a single crystal substrate for epitaxial growth obtained therefrom. Therefore, there is little adverse effect on the thin film when the thin film is formed on the substrate, and it is suitable as a substrate for a light-emitting element that realizes a remarkable reduction in dislocation generation from film formation during device operation.

DESCRIPTION OF SYMBOLS 11 Zinc oxide single crystal growth apparatus 12 High pressure autoclave 13 Autoclave accommodating part 14 Autoclave main body 15 Packing member 16 Cover body 17 Screws 21 and 22 Heater 23 Heat insulating material 31 Zinc oxide single crystal growth container 32 Frame 33 Support tool 34 Internal baffle plate 35 Baffle ring 37 Lid 38 Micro openings 41a to 41d Seed crystal 51 Starting material

Claims (6)

In a hexagonal wurtzite compound single crystal having an a-axis of 120 ° in a regular hexagonal plane and a c-axis perpendicular to the a-axis,
In a matrix region having a continuous and uniform crystal lattice, an island-like crystal microdomain having a different crystal lattice arrangement from the matrix region is included, and the c-axis in the crystal microdomain is c in the matrix region. Parallel to the axis,
When an arbitrary cross section of the wurtzite compound single crystal is observed at 20 crystal lattice images randomly in a 70 nm × 40 nm region with a transmission electron microscope at an observation magnification of 1.5 million, the inside of the matrix region is The crystal microdomain having a size of 3 to 50 nm that is discontinuous with the same direction of the matrix region and the crystal lattice exists, and the ratio of the area of the crystal microdomain is, on average, the entire observation location more than 50% of Ah is,
The wurtzite type compound single crystal, ZnO, ZnMgO, ZnCdO, ZnCuO , ZnOS, hexagonal wurtzite type compound single crystal, wherein a material der Rukoto selected from ZnOSe.   The size of the crystal microdomain is 3 to 50 nm, and the sum of the cross-sectional areas of the crystal microdomains when observed in an arbitrary plane is 50 with respect to the cross-sectional area of the matrix region other than the crystal microdomains. The hexagonal wurtzite type compound single crystal according to claim 1, characterized in that it is at least%.   The hexagonal wurtzite compound single crystal according to claim 1 or 2, wherein the half-value width of the rocking curve of the 0002 plane measured by X-ray diffraction method is 25 arcsec or more and 250 arcsec or less. The hexagonal wurtzite according to claim 1, 2 or 3, wherein the dislocation density observed with a transmission electron microscope is 1 x 10 ⁴ / cm ² or more and 9 x 10 ⁶ / cm ² or less. Ore compound single crystal. 5. The hexagonal wurtzite compound unit according to claim 1, wherein the Li concentration in the crystal is 1 × 10 ¹² / cm ³ or more and 9 × 10 ¹⁵ / cm ³ or less. crystal. A single crystal substrate for epitaxial growth comprising the hexagonal wurtzite compound single crystal according to any one of claims 1 to 5 .

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