JP2006225213A - Zinc oxide single crystal, substrate for epitaxial growth obtained from the same, and methods for manufacturing them - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a zinc oxide single crystal having such a composition that oxygen and zinc are substantially stoichiometrically equal in amount, that is to say, a stoichiometry composition and having extremely high electric specific resistance, and to provide a substrate for epitaxial growth obtained from the same and methods for manufacturing them. <P>SOLUTION: The zinc oxide single crystal is provided which has such a composition that oxygen and zinc are substantially stoichiometrically equal in amount and which has electric specific resistance of ≥1×10<SP>9</SP>Ω cm. The substrate for epitaxial growth obtained from the same, and methods for manufacturing them are also provided. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a zinc oxide single crystal having a stoichiometric composition, a zinc oxide single crystal substrate used for a substrate for epitaxial growth obtained therefrom, and a method for producing them.

Zinc oxide is a material that has been known for a long time and has been used as an industrial chemical such as a catalyst and cosmetics. However, zinc oxide has recently been reviewed as a semiconductor because it is a direct transition type wide band gap semiconductor, and in recent years, it has been widely applied to semiconductor devices such as blue LEDs (Light Emitting Diodes) and LDs (Laser Diodes). It is expected and attracting attention. It is known that this zinc oxide single crystal can be produced by a hydrothermal method. Generally, artificial crystals are widely known for the production of single crystals by the hydrothermal method, but zinc oxide single crystals can also be implemented in the same manner. For example, as shown in Non-Patent Document 1, a typical example of a manufacturing condition of a zinc oxide single crystal by a hydrothermal method is shown below. A small piece of zinc oxide single crystal is used as a seed crystal, the raw material is a zinc oxide sintered body, and the solvent is 6.5 mol / L potassium hydroxide and 0.1 to 2 mol / L lithium hydroxide. Put in (Ag, Pt) crucible and seal. Then, this is inserted into an autoclave and grown over several weeks at a growth temperature of 300 to 400 ° C. and a pressure of 55 MPa. However, conventionally grown ones have low single crystallinity and inferior quality, such as contamination with impurities and coloring. For example, these conventional grown zinc oxide single crystals have a low electrical resistivity of about 10 ^{−1 to 5} Ω · cm. This is because the stoichiometric ratio of oxygen atoms and zinc atoms constituting zinc oxide is not equivalent to 1: 1, but shifted to the oxygen deficiency side, in other words, the composition shifted to the zinc excess side. It is thought to do. That is, it is presumed that the electrical resistivity decreased because the balance of oxygen and zinc charges in the zinc oxide single crystal was lost as the oxygen deficiency increased.

  The crystallinity of such a zinc oxide single crystal with many oxygen vacancies is not sufficient. Oxygen vacancies themselves become crystal defects, and other impurities may be mixed into the vacancy, causing dislocations, etc. There is a concern that the number of crystal defects increases. In order to be used as the blue LED, LD, or substrate thereof, a high-quality zinc oxide single crystal excellent in single crystallinity is essential. That is, suppression of crystal defects in the zinc oxide single crystal, in other words, reduction of oxygen vacancies in the zinc oxide single crystal is essential, and this is one of the major problems.

  As for application to dielectrics, there has been no zinc oxide single crystal having high single crystallinity and high electrical resistivity so far.

R. A. Laudise et. al. J. et al. Am. Ceram. Soc. 47, 9, 1964

  Industrially, as a new material that can be used for blue LEDs, LD, or their substrates, dielectrics, and the like, development of zinc oxide single crystals and substrates excellent in single crystallinity of stoichiometric composition is strongly desired. For this reason, an object of the present invention is to provide a composition in which oxygen and zinc are substantially stoichiometrically equivalent, that is, a zinc oxide single crystal having a stoichiometric composition and extremely high electrical resistivity, the zinc oxide single crystal It is another object of the present invention to provide a substrate for epitaxial growth and a method for producing them.

  In order to solve these conventional problems, the present inventors diligently studied the hydrothermal production conditions of the zinc oxide single crystal, the physical properties of the obtained single crystal, and the modification of the single crystal. As a result, a zinc oxide single crystal having an unprecedented stoichiometric composition was invented. The single crystal has a high electrical resistivity, that is, suggests that oxygen and zinc constituting zinc oxide are substantially stoichiometrically equivalent. In addition, the single crystal can be solved in a gold container by introducing an oxygen generator in a hydrothermal method, and all the conventional problems can be solved, and the single crystal can be further treated by heat treatment. The present inventors have found that a great effect that is not possible can be obtained, and have completed the present invention.

That is, the present invention relates to a zinc oxide single crystal having a composition in which oxygen and zinc are substantially stoichiometrically equivalent, that is, a stoichiometric composition, and having an electrical resistivity of 1 × 10 ⁹ Ω · cm or more. is there. Further, it is an epitaxial growth substrate obtained by cutting or processing the zinc oxide single crystal by a known method.

  In addition, the present invention is manufactured using a zinc oxide powder sintered body, which is a raw material for zinc oxide single crystal, previously charged in a container made of gold or the like and hydrothermally treated in an aqueous hydrogen peroxide solution using an autoclave apparatus. Zinc oxide single crystal.

  Furthermore, the present invention provides a single crystal growth vessel in which the hydrothermally treated zinc oxide powder sintered body is charged, a small piece of zinc oxide single crystal is suspended as a seed crystal, an alkali metal hydroxide aqueous solution and barium peroxide, One or more oxygen generators selected from the group consisting of calcium oxide, hydrogen peroxide, sodium percarbonate, potassium percarbonate, lithium percarbonate, and sodium perborate are added, and this is sealed and autoclaved. This is a method for producing a zinc oxide single crystal by a hydrothermal method in which it is inserted into an apparatus and grown by growing a seed crystal under high temperature and high pressure.

  Moreover, this invention is a manufacturing method of the zinc oxide single crystal which heat-processes this zinc oxide single crystal in oxygen and / or nitrogen gas at the temperature of 800 degreeC or more.

  In addition, the present invention provides a method for producing an epitaxial growth substrate in which an epitaxial growth substrate obtained by processing a zinc oxide single crystal substrate is further heat-treated in oxygen and / or nitrogen gas at a temperature of 800 ° C. or higher, and this method is obtained. This is a substrate for epitaxial growth.

  Hereinafter, the present invention will be described in detail.

As described above, the present invention is a zinc oxide single crystal having a stoichiometric composition, and the single crystal has an electric resistivity of 1 × 10 ⁹ Ω · cm or more. The fact that the electrical specific resistance shows a very high value of 1 × 10 ⁹ Ω · cm or more means that oxygen and zinc constituting the zinc oxide single crystal of the present invention are substantially stoichiometrically equivalent, and stoichiometric. This suggests that it is a metric composition. Here, “substantially stoichiometric equivalent of oxygen and zinc” means that the oxygen and zinc that form zinc oxide are theoretically equivalent, but the electrical resistivity is substantially equal. Means a high electrical resistivity of 1 × 10 ⁹ Ω · cm or more.

  The zinc oxide single crystal of the present invention is colorless and transparent with an alkali metal impurity derived from an aqueous alkali metal hydroxide solution used as a growth solvent of 10 ppm by weight or less, and an external light transmittance of 75% or more in the visible region, and Zinc oxide single crystal with high quality and excellent single crystallinity with peak half-value width of (0004) plane perpendicular to c-axis of zinc oxide single crystal measured by X-ray diffractometry by X-ray diffraction method is 25 seconds or less is there.

Conventional zinc oxide single crystals have a large amount of oxygen ^vacancies , and therefore the electrical specific resistance is as low as about 10 ^{−1 to 5} Ω · cm. The zinc oxide single crystal of the present invention has a stoichiometric composition and its electrical specific resistance is as high as 1 × 10 ⁹ Ω · cm or more, and therefore, it is a high-quality single crystal excellent in single crystallinity. It is essential to be.

  It is considered that the electrical resistivity of the zinc oxide single crystal is such that the larger the value, the fewer crystal defects and the higher the quality of the zinc oxide single crystal. The reason is that the zinc oxide compound is prone to oxygen deficiency. The smaller the oxygen deficiency, the closer the oxygen and zinc that make up the zinc oxide single crystal are stoichiometrically equivalent. This is because the electric charge balance is maintained and the electrical resistivity increases.

The electrical resistivity of the zinc oxide single crystal of the present invention is 1 × 10 ⁹ Ω · cm or more, preferably 10 ¹¹ Ω · cm or more, more preferably 10 ¹² Ω · cm or more. On the other hand, when the electrical resistivity of the zinc oxide single crystal is smaller than 1 × 10 ⁹ Ω · cm, there are relatively many oxygen vacancies in the zinc oxide single crystal, and it is considered that there are many crystal defects. Inferior crystallinity is expected and not preferred.

  Moreover, the zinc oxide single crystal of the present invention is characterized by high purity and few impurities. Specific examples of impurities include K and Li derived from a single crystal growth solvent, Au or Pt as a growth container material, and the total content thereof is 10 ppm or less, preferably 5 ppm or less, more preferably 1 ppm or less. It is. If these impurities exceed 10 ppm, the crystallinity and the like of the zinc oxide single crystal is lowered, which is not preferable.

  The zinc oxide single crystal of the present invention is colorless and transparent. The optical external transmittance (UV-3100PC, manufactured by Shimadzu Corporation) at a wavelength in the visible region of the substrate for epitaxial growth obtained from the zinc oxide single crystal of the present invention is 75% or more when measured with a 1 mm thick substrate, for example. Yes, preferably 80% or more. Those having an external light transmittance of less than 75% exhibit coloring, which is considered to be caused by impurity contamination, crystal defects, and the like, which may be undesirable.

  Moreover, the single crystallinity of the zinc oxide single crystal can be seen by the half width of the X-ray rocking curve measurement by the X-ray diffraction method, and the smaller the half width, the better the single crystallinity. The peak half width of the (0004) plane of the zinc oxide single crystal of the present invention is 25 (optical system: incident / artificial multilayer mirror + Ge (440) -4 crystal optical system, light receiving / Ge (002) -2 crystal analyzer). It is not more than seconds, preferably not more than 20 seconds, more preferably not more than 15 seconds, and it is extremely excellent in single crystallinity close to a theoretical perfect crystal without oxygen deficiency. When the peak half width of the zinc oxide (0004) surface exceeds 25 seconds, the single crystallinity becomes insufficient. For example, when the single crystal is used as a substrate crystal for epitaxial growth for LEDs, the single crystallinity of the zinc oxide Insufficient quality, i.e., crystal defects may adversely affect the single crystal epitaxially grown.

  The present invention is an epitaxial growth substrate obtained by processing a zinc oxide single crystal by cutting or the like.

  The substrate for epitaxial growth is a substrate for epitaxial crystal film growth in devices such as GaN-based and ZnO-based blue LEDs and LDs. The substrate is obtained by processing the zinc oxide single crystal according to the present invention, and the processing method may be a general method. An example is shown. A substrate is obtained by slicing with a diamond cutter along the (0001) plane perpendicular to the c-axis of the zinc oxide single crystal, and processing and modifying this by polishing, wet etching, heat treatment or the like.

A conventional zinc oxide single crystal substrate has a large amount of oxygen vacancies, and therefore has a large number of crystal defects and is inferior in quality, so that it is not sufficient as an epitaxial growth substrate. The epitaxial growth substrate of the present invention has a stoichiometric composition free of oxygen vacancies and is considered to be used as a high-quality substrate with extremely few crystal defects.
Further, the present invention is a zinc oxide single crystal obtained by using a zinc oxide powder sintered body hydrothermally treated in an aqueous hydrogen peroxide solution using an autoclave apparatus as a raw material for the zinc oxide single crystal.

  Furthermore, the present invention provides a hydrothermally treated zinc oxide powder sintered body as a raw material at the bottom of a single crystal growth vessel, suspends a small piece of zinc oxide single crystal as a seed crystal at the top, and an alkali metal hydroxide aqueous solution. And one or more oxygen generators selected from the group consisting of barium peroxide, calcium peroxide, hydrogen peroxide, sodium percarbonate, potassium percarbonate, lithium percarbonate and sodium perborate. This is a method for producing a zinc oxide single crystal having a stoichiometric composition by a hydrothermal method of growing a zinc oxide single crystal under high temperature and high pressure using an autoclave apparatus.

  Hereinafter, the manufacturing method will be described, but the manufacturing method of the zinc oxide single crystal and the substrate for epitaxial growth of the present invention is not limited to this manufacturing method.

  In the present invention, a single crystal growth vessel made of gold or the like is charged with a sintered body obtained from zinc oxide powder previously hydrothermally treated in an aqueous hydrogen peroxide solution using an autoclave apparatus, and oxidized as a seed crystal. While hanging a small piece of zinc single crystal, charging with an alkali metal hydroxide aqueous solution, adding an oxygen generator to this, it was sealed and inserted into an autoclave, hydrothermally at a temperature of 300 to 450 ° C. and a pressure of 50 to 130 MPa. Grow and manufacture.

  The zinc oxide sintered body which is the raw material of the present invention is formed by sintering zinc oxide powder by cold isostatic pressing or the like, and then sintering the sintered body in an aqueous hydrogen peroxide solution using an autoclave device. Heat-treated. This is a process intended to recrystallize the sintered body as a raw material with few oxygen vacancies by coexisting hydrogen peroxide when the sintered body is recrystallized and purified. Become. The method for treating the sintered body is that the sintered body, water and hydrogen peroxide solution are charged in a container such as a metal container and then sealed and inserted into an autoclave apparatus, and the temperature is 100 ° C. or higher, more preferably 200 ° C. or higher. Even more preferably, it is a method of treating at a high temperature and a high pressure of 300 to 450 ° C. and a pressure of 50 to 130 MPa, the same as the single crystal growth conditions. The amount of hydrogen peroxide may be such that the generated oxygen pressure is 0.01 MPa or more, and preferably 0.1 MPa or more. When the oxygen pressure is less than 0.01 MPa, the above-described effect is reduced.

  Moreover, the average particle diameter of the zinc oxide powder which is the precursor of the sintered body is preferably 30 μm or less, more preferably 10 μm or less, and further preferably 1 μm or less. If it exceeds 30 μm, the contact area between the particles becomes smaller during the formation and / or sintering of the zinc oxide powder, so that the sintering density is finally lowered. There is a concern that it will collapse into powder. When it becomes powdery, it is scattered in the growth vessel, causing nucleation in the growth region, which may hinder seed crystal growth.

  The particle size distribution of the powder may be sharp, but may be broad to some extent, that is, the larger the contact area between the particles, the better.

In order to increase the sintered density, it is also effective that the specific surface area of the raw material powder is large. Preferably it is 2 m < ² > / g, More preferably, it is 4 m < ² > / g, More preferably, it is 8 m < ² > / g. If it is less than 2 m ² / g, the sintered density may not increase as expected.

  Examples of oxygen generators used in the production of zinc oxide single crystals include compounds that generate oxygen, such as barium peroxide, calcium peroxide, hydrogen peroxide, sodium percarbonate, potassium percarbonate, lithium percarbonate, and sodium perborate. Any barium peroxide is preferably used. These oxygen generators may be used alone or in combination of two or more.

  Barium peroxide is preferable because barium peroxide is a stable substance at room temperature and has excellent quantitative properties, and decomposes under hot water to generate oxygen, which makes it extremely useful as an oxygen generator of the present invention. It is. At the same time, barium hydroxide produced by decomposition has a very high solubility in water and the ionic radius of barium is large, so that it is not mixed into the zinc oxide single crystal growing as a single crystal, which is also preferable. .

  The amount of the oxygen generator may be such that the oxygen pressure generated during single crystal growth is 0.01 MPa or more, preferably 0.1 MPa or more, more preferably 1 MPa or more. When the oxygen pressure is less than 0.01 MPa, it is insufficient for obtaining the zinc oxide single crystal of the present invention. Moreover, although it does not specifically limit in the quantity exceeding 1 Mpa, The characteristic of the zinc oxide single crystal of this invention will hardly change even if it makes it excessive further.

  Further, in the oxygen generator, hydrogen peroxide as well as barium peroxide and the like are extremely decomposable under hot water, and it can be considered that all the compounds are decomposed to generate oxygen.

  The growth temperature of the zinc oxide single crystal by the hydrothermal method of the present invention is not particularly limited. If it is between 300 to 450 degreeC conventionally performed, there is no problem. However, in order for the preferable zinc oxide single crystal to have high single crystallinity, the difference between the temperature of the single crystal growth region at the top of the growth vessel and the temperature of the raw material zinc oxide sintered body region at the bottom is important. Specifically, the temperature difference between the high temperature raw material melting region and the low temperature single crystal growth region is 10 ° C. or less, preferably 8 ° C. or less, more preferably 6 ° C. or less and 1 ° C. or more. If the temperature exceeds 10 ° C., the supersaturation degree of zinc oxide may collapse at once and nucleation may occur, thereby inhibiting efficient growth of seed crystals. On the other hand, when the temperature is lower than 1 ° C., the seed crystal may be melted or the growth rate of the seed crystal may be rapidly reduced, resulting in poor productivity.

  In the autoclave for producing the zinc oxide single crystal of the present invention, the material for the single crystal growing vessel is preferably made of gold (Au). As a result of intensive studies on the material of the single crystal growing container, the present inventors have found an unexpectedly large effect. That is, when an alkali metal hydroxide aqueous solution and / or an oxygen generator is used under hydrothermal conditions, it has been found that not all noble metals are excellent in corrosion resistance. Among the noble metals, Au was remarkably excellent in corrosion resistance under the conditions for producing the zinc oxide single crystal according to the present invention.

  Conventionally, platinum (Pt) has been used as a noble metal, but it has been found that Pt is slightly dissolved in an aqueous alkali metal hydroxide solution, and its solubility increases under hot water. That is, it is not preferable to use a Pt container in the production of zinc oxide single crystal using an alkali metal hydroxide aqueous solution because Pt is dissolved in the growth solution and contaminated as an impurity in the growth process of the zinc oxide single crystal. There is. It was also found that when barium peroxide as an oxygen generating agent of the present invention or a combination agent of barium peroxide and hydrogen peroxide was charged, the corrosion resistance of Pt was further deteriorated, and the degree of contamination deteriorated.

  Further, Au is advantageous in terms of function and cost as compared with Pt. Specifically, since Au is more ductile than Pt, it can flexibly cope with changes in pressure during single crystal production.

  A small piece of zinc oxide single crystal used as a seed crystal in the present invention is flattened by polishing and / or chemical mechanical polishing, and further heat treated in oxygen and / or nitrogen gas at a temperature of 800 ° C. or higher. Good. This is because the flatness and crystallinity of the seed crystal surface are improved by the treatment, and a high-quality single crystal is grown in the seed crystal growth at the time of manufacture. On the other hand, it is feared that the seed crystal having a rough surface grows to an unfavorable crystallinity.

  The total amount of metal impurities contained in the zinc oxide as the raw material of the present invention is preferably less than 100 ppm by weight. More preferably, it is 10 ppm by weight or less. At this time, the element of impurity incorporation into the zinc oxide single crystal to be manufactured becomes extremely small, and a high-purity zinc oxide single crystal can be manufactured.

  The total amount of metal impurities contained in the alkali metal aqueous solution of the solvent of the present invention is preferably less than 100 ppm by weight. More preferably, it is 10 ppm by weight or less. At this time, as described above, the element of impurity incorporation into the zinc oxide single crystal to be manufactured becomes extremely small, and a high-purity zinc oxide single crystal can be manufactured.

  The zinc oxide single crystal obtained by the present invention and the substrate for epitaxial growth obtained by processing it are heat-treated in oxygen and / or nitrogen gas at a temperature of 800 ° C. or higher. At this time, the obtained zinc oxide single crystal and the substrate for epitaxial growth are further increased in resistance, become high single crystal, and quality is improved. Further, the surface of the zinc oxide single crystal or the epitaxial growth substrate is flattened at the atomic level by the heat treatment, and a step terrace is formed. This is very useful when an epitaxially grown crystal is deposited on the substrate smoothly when used as an epitaxial growth substrate.

  The heat treatment temperature is preferably 800 ° C. or higher, more preferably 1000 ° C. or higher, and particularly preferably 1100 ° C. or higher. If it is less than 800 degreeC, the effect of the quality improvement of a zinc oxide single crystal mentioned above may become inadequate. Zinc oxide has a property of easily adsorbing carbonic acid, and if it is less than 800 ° C., its desorption may be insufficient.

  The atmosphere for the heat treatment may be any as long as it is in oxygen and / or nitrogen gas. In addition, zinc oxide powder or a sintered body made of the zinc oxide may be placed around the heat treatment. The reason is that zinc oxide is a sublimable compound and has a property of starting to sublimate from about 1300 ° C., which can keep the vapor pressure of zinc oxide constant and prevent alteration of the zinc oxide single crystal. Because it is considered.

  Further, the zinc oxide single crystal or the epitaxial growth substrate is preferably sandwiched between oxygen supply type compounds such as yttrium-stabilized zirconia. The reason is that it is considered that the zinc oxide single crystal and the epitaxial growth substrate can prevent oxygen deficiency during heat treatment at high temperature.

The present invention has the following effects.
(1) The zinc oxide single crystal of the present invention and the substrate for epitaxial growth obtained therefrom are zinc oxide having an unprecedented stoichiometric composition, have high electrical specific resistance, and have excellent single crystallinity. Is a good quality single crystal with very few crystal defects. Therefore, the zinc oxide single crystal and the substrate obtained therefrom are very useful as a blue LED, LD, and their substrates that can achieve high performance.
(2) The method for producing the zinc oxide single crystal of the present invention and the substrate for epitaxial growth obtained therefrom is based on a growth method under high temperature and high pressure using an autoclave apparatus. Using high-purity, high-quality zinc oxide single-crystal with an unprecedented stoichiometric composition by using a solution treated with hydrogen peroxide in water, using a gold growth vessel, and introducing an oxygen generator. Crystals can be obtained by a simple, industrial and economical production method, and are extremely useful industrially.

  Examples of the present invention and comparative examples are shown below, but the present invention is not limited to these examples. Parts,% and ppm are based on weight.

Example 1
In single crystal production by a hydrothermal method using an autoclave apparatus, a gold growth vessel is used as a single crystal growth vessel, 100 parts of a sintered body obtained from zinc oxide powder, 3 mol / L of potassium hydroxide aqueous solution, A (0001) plane plate perpendicular to the c-axis of a zinc oxide single crystal as a seed crystal was charged with 125 parts of a 1.5 mol / L aqueous lithium hydroxide solution and 2.4 parts of barium peroxide as an oxygen generator. A small piece was suspended, this gold container was sealed, and a zinc oxide single crystal (A) was grown at 370 ° C. under 100 MPa for 2 weeks. The sintered body obtained from the zinc oxide powder used as a raw material was previously charged in a gold container using an autoclave apparatus, and 100 parts of a 30% hydrogen peroxide aqueous solution and 125 parts of water were added. The gold container was sealed and treated at 370 ° C. under 100 MPa for 2 days. Next, the substrate (A) was prepared by cutting out from the single crystal (A) to the thickness of 1 mm on the (0001) plane on the zinc termination surface side. The zinc oxide single crystal is crystallographically hexagonal and wurtzite, and has a layered structure composed of repeating layers composed of zinc and oxygen on a plane perpendicular to the c-axis. In the (0001) plane of zinc single crystal, there are zinc termination and oxygen termination.

  And about a board | substrate (A), the electrical resistance was measured and the electrical specific resistance was calculated | required. For the electrical resistance measurement, a zinc oxide single crystal substrate provided with an indium-gallium electrode is placed in a dark box using an ampere meter, and along the (0001) orientation of the zinc oxide crystal substrate by a direct current-voltage two-terminal method. Measured. In addition, the electrode used indium-gallium and confirmed ohmic by the current-voltage characteristic.

The electrical resistivity of the substrate (A) was 9 × 10 ¹⁰ Ω · cm, and the difference from the substrate (B) shown in Comparative Example 1 below was clear.

Further, X-ray diffraction / X-ray rocking curve measurement was performed under the following conditions.
<X-ray diffractometer and conditions>
Substrate measurement lattice plane: (0004)
Measuring device: ATX-E
X-ray source: rotating counter cathode Cu target (50 kV-300 mA)
Measurement optical system: incident optical system, artificial multilayer mirror + Ge440-4 crystal optical system
Light receiving optical system / Ge220-2 crystal analyzer As a result, it was found that the (0004) peak half-value width of the substrate (A) was as sharp as 15 seconds and excellent in single crystallinity. On the other hand, the substrate (B) shown in Comparative Example 1 below was inferior in single-crystal property to the substrate (A) for 26 seconds.
Further, impurity analysis was performed by ICP measurement of the substrate (A) (apparatus: SPS1200A Plasma Spectrometer, manufactured by Seiko Instruments Inc.).
As a result, Li and K derived from the alkali metal hydroxide used as the single crystal solvent were less than 1 ppm in total, and Au and Pt derived from the single crystal growth vessel were not detected and were less than 1 ppm.
(Comparative Example 1)
In the operation of Example 1, a zinc oxide single crystal (B) was obtained by the same operation except that barium peroxide as an oxygen generating agent was not added. A substrate (B) cut out to 1 mm was prepared.

And about the board | substrate (B), when electrical resistance was measured similarly to Example 1 and the electrical specific resistance was calculated | required, it was 2 * 10 < ⁵ > ohm * cm, and it is with the board | substrate (A) by said Example 1 above. The difference was clear.

  Further, when X-ray diffraction / X-ray rocking curve measurement was performed under the same conditions as in Example 1, the (0004) peak half-value width of the substrate (B) was 26 seconds, and the substrate (A) according to Example 1 described above was found. The single crystallinity was inferior.

  Further, as a result of ICP measurement of the substrate (B) in the same manner as in Example 1, Li and K were less than 1 ppm in total, and Au and Pt were not detected, and were less than 1 ppm.

  From the results of Example 1 and Comparative Example 1 described above, the specific content of the electrical resistivity is greatly different from the amount of oxygen deficiency even though the impurity content of the zinc oxide substrate is low and similar. The substrate (A) according to Example 1 was considered to be a stoichiometric zinc oxide single crystal having very few oxygen vacancies and excellent in single crystal.

(Example 2)
A zinc oxide single crystal was obtained in the same manner as in Example 1 except that 8 parts of barium peroxide was added as an oxygen generator, and a substrate cut out from the (0001) plane on the zinc termination surface side was obtained. The electrical resistivity of the substrate was 6 × 10 ¹² Ω · cm.

(Example 3)
A zinc oxide single crystal was obtained in the same manner as in Example 1 except that 0.8 part of barium peroxide was added as an oxygen generator, and a substrate cut out from the (0001) plane on the zinc termination surface side was obtained. The electrical resistivity of the substrate was 3 × 10 ⁹ Ω · cm.

Example 4
A zinc oxide single crystal was obtained in the same manner as in Example 1 except that 0.8 part of hydrogen peroxide was added as an oxygen generator, and a substrate cut out from the (0001) plane on the zinc termination surface side was obtained. The electrical resistivity of the substrate was 1 × 10 ⁹ Ω · cm.

(Example 5)
A zinc oxide single crystal was obtained in the same manner as in Example 1 except that 1.2 parts of barium peroxide and 1.2 parts of hydrogen peroxide were added as oxygen generators. A substrate cut out in the (0001) plane was obtained. The electrical resistivity of the substrate was 4 × 10 ¹⁰ Ω · cm.

(Comparative Example 2)
A zinc oxide single crystal was obtained in the same manner as in Example 1 except that a platinum vessel was used as the single crystal growth vessel, and a substrate cut out from the (0001) plane on the zinc termination surface side was obtained. The electrical resistivity of the substrate was 7 × 10 ¹⁰ Ω · cm. However, the Pt container changed color and was severely corroded. Furthermore, the impurity analysis by ICP of the substrate detected Pt of 1 ppm or more, which caused the platinum container to corrode and cause Pt contamination to the zinc oxide single crystal.

(Comparative Example 3)
A zinc oxide single crystal was obtained in the same manner as in Example 1 except that a platinum vessel was used as a single crystal growth vessel and 2.4 parts of hydrogen peroxide was added as an oxygen generator. A substrate cut out in the (0001) plane was obtained. The electrical resistivity of the substrate was 6 × 10 ⁹ Ω · cm. However, the Pt container changed color and was severely corroded. Furthermore, the impurity analysis of the substrate by ICP detected Pt of 1 ppm or more, and the corroded Pt caused contamination of the zinc oxide single crystal.

  The operating conditions and results of Examples 1 to 5 and Comparative Examples 1 to 3 are summarized in Table 1.

（実施例６）
実施例１で得た酸化亜鉛単結晶基板を、管状炉を用いて、８００℃で２時間、酸素気流下で熱処理した。酸化亜鉛基板は鏡面状の（１１１）イットリウム安定化ジルコニア（ＹＳＺ）単結晶で挟んで、周囲には酸化亜鉛粉末を堆積した。熱処理した該基板の電気比抵抗は４×１０^１１Ω・ｃｍであった。また、実施例１記載と同条件で、Ｘ線回折・Ｘ線ロッキングカーブ測定した結果、熱処理した該基板の（０００４）ピーク半値幅は１４．８秒と極めてシャープだった。

(Example 6)
The zinc oxide single crystal substrate obtained in Example 1 was heat-treated at 800 ° C. for 2 hours under an oxygen stream using a tubular furnace. The zinc oxide substrate was sandwiched between mirror-like (111) yttrium-stabilized zirconia (YSZ) single crystals, and zinc oxide powder was deposited around it. The electrical resistivity of the heat-treated substrate was 4 × 10 ¹¹ Ω · cm. Further, as a result of X-ray diffraction / X-ray rocking curve measurement under the same conditions as described in Example 1, the (0004) peak half-value width of the heat-treated substrate was extremely sharp at 14.8 seconds.

(Example 7)
The zinc oxide single crystal substrate was heat-treated in the same manner as in Example 5 except that the heat treatment atmosphere was changed to a nitrogen stream. The electrical specific resistance after the heat treatment was 1 × 10 ¹¹ Ω · cm.

(Example 8)
Except that the heat treatment temperature was 1200 ° C., the zinc oxide single crystal substrate was heat treated in the same manner as in Example 5. The electrical specific resistance after the heat treatment was 8 × 10 ¹¹ Ω · cm.

(Comparative Example 4)
Except that the heat treatment temperature was 600 ° C., the zinc oxide single crystal substrate was heat treated in the same manner as in Example 5. The electrical specific resistance after the heat treatment was 9 × 10 ¹⁰ Ω · cm.

  The operating conditions and results of Examples 6 to 8 and Comparative Example 4 are summarized in Table 2.

Claims (9)

A zinc oxide single crystal having a composition in which oxygen and zinc are substantially stoichiometrically equal and having an electrical resistivity of 1 × 10 ⁹ Ω · cm or more. The zinc oxide single crystal according to claim 1, wherein the zinc oxide powder sintered body used as a raw material for the zinc oxide single crystal is hydrothermally treated in an aqueous hydrogen peroxide solution using an autoclave apparatus. A zinc oxide powder sintered body is charged at the bottom of the single crystal growth container as a raw material, and a small piece of zinc oxide single crystal is suspended as a seed crystal at the top, while an alkali metal hydroxide aqueous solution and barium peroxide, calcium peroxide, One or more oxygen generators selected from the group consisting of hydrogen oxide, sodium percarbonate, potassium percarbonate, lithium percarbonate, and sodium perborate are added, and the autoclave apparatus is used under high temperature and high pressure. The method for producing a zinc oxide single crystal according to claim 1 or 2, wherein the zinc oxide single crystal is grown. The method for producing a zinc oxide single crystal according to claim 3, wherein the oxygen generator is barium peroxide or barium peroxide and hydrogen peroxide. The method for producing a zinc oxide single crystal according to claim 3 or 4, wherein the material for growing the single crystal is gold. The method for producing a zinc oxide single crystal according to any one of claims 3 to 5, wherein the zinc oxide single crystal is heat-treated at a temperature of 800 ° C or higher in oxygen and / or nitrogen gas. An epitaxial growth substrate obtained from the zinc oxide single crystal according to claim 1. The epitaxial growth substrate according to claim 7, wherein the zinc oxide powder sintered body used as a raw material for the zinc oxide single crystal is hydrothermally treated in an aqueous hydrogen peroxide solution using an autoclave apparatus. A method for producing an epitaxial growth substrate, wherein the epitaxial growth substrate according to claim 7 or 8 is further heat-treated in oxygen and / or nitrogen gas at a temperature of 800 ° C or higher.