JP3548910B2 - Method for producing ZnO single crystal - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for producing a single crystal by a zinc oxide solution drawing method and a solvent transfer zone melting method, and a method for forming a single crystal film by liquid phase growth.
[0002]
[Prior art]
Zinc oxide is an interesting substance that can be a direct transition semiconductor having a band gap of 3.3 eV while being an oxide, and is a material that can be expected to be applied as a blue-ultraviolet light-emitting material. In addition, it exhibits piezoelectricity, fluorescence, and photoconductivity, has various functions, and is a substance that can be widely applied. For that purpose, a large-sized high-quality single crystal is required, and development of a manufacturing method thereof is desired.
Since ZnO has a high melting point of 1975 ° C. and is a substance that is easily evaporated, a single crystal cannot be manufactured from a raw material having the same composition as a single crystal.
Therefore, the Czochralski method cannot be applied. Therefore, a single crystal is prepared by mixing the target substance (ZnO) with a solvent, lowering the temperature of the mixed solution to bring the mixed solution to a state of supersaturated concentration or higher, and precipitating the target substance as a single crystal from the melt to obtain a single crystal. And a hydrothermal synthesis method have been adopted as production methods.
However, a large single crystal which is long in the desired crystal axis direction cannot be obtained, and there is a disadvantage that the crystal production requires a long time.
[0003]
In the stationary slow cooling method, PbF ₂ is often used as a solvent, and an example in which a large crystal of 30 × 30 mm is grown has been reported (Ref. 1 JW Nielsen and EF Dearborn J. Phys. Chem. 64, (1960) 1762).
While Wanklyn used V ₂ O ₅ or P ₂ O ₅ as a solvent, it also used V ₂ O ₅ alone (Ref. 2 BM Wanklyn J. Cryst. Growth 7, (1970) 107). .
However, the phase diagram of the ZnO-V ₂ O ₅ system referred to by us (Reference 3 VA Akamarov, AA Fotiev and LN. SereBryakova, Zh. Neorg. Kim., 16, 1971) 2849) was reported before it was published, so ZnO was grown from a composition outside the composition range (ZnO: V ₂ O ₅ = 3: 1 and 2.84: 1) in which ZnO single crystals were precipitated as primary crystals. It is strange that a single crystal was grown.
Although a ZnO single crystal is also produced by hydrothermal synthesis, (Reference 4 RA Laudise, ED Kolb and AJ Caporaso, J. Am. Ceram. Soc., 47, (1964) 9, References 5 Sekiguchi, Miyashita, "Ohara, Shishido, Sakagami, Journal of Crystal Growth, 26, (1999) 39) It takes 10 to 20 days to obtain a single crystal about 1 cm in size. You can see that
[0004]
[Problems to be solved by the invention]
As described above, the crystals grown in the stationary slow cooling method are plate-like and not very large. The hydrothermal synthesis method has a disadvantage that it takes a long time of 10 to 20 days to grow crystals.
[0005]
[Means to solve the problem]
The present invention has been made in view of such a point, and a solution in a composition range capable of precipitating ZnO as a primary crystal is composed of zinc oxide, vanadium oxide, and boron oxide, and the melt is cooled. By doing so, ZnO microcrystals precipitated in the melt are crystallized on the seed crystal contacted with the melt and on a substrate, and this is produced as a ZnO single crystal by a solution drawing method and a solvent transfer zone melting method. And a method of manufacturing a ZnO single crystal film by a liquid phase growth method. Unlike the stationary slow cooling method, a high-quality single crystal of any size in a desired direction can be produced on a seed crystal or a substrate in a short time.
[0006]
First, the principle of the present invention will be described. FIG. 1 is a phase diagram of the ZnO—V ₂ O ₅ system (Reference Document 3). A liquidus exists in a composition in which ZnO is 75 to 100 mol% and V ₂ O ₅ is 25 to 0 mol%. Raw materials having a mixed composition during this period are melted at a temperature on the liquidus, and the melt is gradually cooled. Then, ZnO is precipitated as a solid phase, and the composition of the melt shifts toward V ₂ O ₅ along the liquidus line. Furthermore, if ZnO is shifted to the left from the point of 75 mol% and V ₂ O ₅ is shifted to 25 mol%, ZnO does not precipitate, but Zn ₄ V ₂ O ₉ precipitates as a solid phase. Precipitation growth is not possible. In this phase diagram, when a small amount of different elements are mixed, if the phase diagram does not change in characteristics, the same ZnO solid solution is precipitated as a solid phase.
[0007]
The 2 and 3 are phase diagram of _ZnO-B 2 _{O 3} system (ref 6 D.E.Harriso andF.A.Hummel, J.Electorochem.Soc., 103 , (1956) 496, reference 7 Yu.S.Leonov, Zhur.Neorg.Kim., 3, (1958) 1246.). A liquidus exists at a composition of about 75 to 100 mol% of ZnO and about 25 to 0 mol% of B ₂ O ₃ , and similarly, the raw material of the mixed composition during this period melts at a temperature on the liquidus line, and When the temperature is gradually lowered, ZnO becomes a solid phase and precipitates, and the composition of the melt shifts to the B ₂ O ₃ side along the liquidus line. further. If ZnO is shifted to the right from the point of 75 mol% and B ₂ O ₃ is shifted to the right by 25 mol%, ZnO does not precipitate, but another phase precipitates as a solid phase (in these phase diagrams, the precipitated phases coincide with each other). However, ZnO cannot be deposited and grown outside the above composition range. In this phase diagram, when a small amount of different elements are mixed, if the phase diagram does not change in characteristics, the same ZnO solid solution is precipitated as a solid phase.
[0008]
Further, the mixing composition ratio of solute ZnO and the solvents V ₂ O ₅ and B ₂ O _{3 is} the same as the composition of ZnO of 75 to 100 mol% and the solvent of 25 to 0 mol%. If the mixture of the solvents V ₂ O ₅ and B ₂ O ₃ does not exceed 25 mol%, use a solvent in which both V ₂ O ₅ and B ₂ O ₃ are mixed at 0 to 100 mol% with each other. In the same way, ZnO can be precipitated as a solid phase in the same manner, and when a small amount of a different kind of element is mixed, if the phase diagram does not change in characteristics, the same ZnO solid solution precipitates as a solid phase. Come.
It is known that the characteristics of ZnO are remarkably changed by mixing different kinds of elements, and Li, Na, K, Cu, Ag, N, P, As, Cr, Al, Bi, Sb, Co, Mn, and Pr are several%. The following are mixed, and there are applications such as p-type semiconductor conversion, conductivity control, and varistor.
In the present invention, a ZnO single crystal in which these crystals are precipitated on the same ZnO or a seed crystal having a lattice constant and a melting point close to each other is grown, and a ZnO single crystal film is grown on the substrate.
[0009]
Examples Hereinafter, the present invention will be described in detail with reference to examples.
Example 1
An example in which a ZnO single crystal is manufactured by a solution drawing method will be described.
FIG. 4 shows the single crystal pulling apparatus used. In FIG. 4, 1 is a lifting shaft, 2 is a platinum shaft, 3 is a heat insulator, 4 is a high frequency heating coil, 5 is a thermocouple, 6 is a crucible support, 7 is a seed crystal, 8 is a grown single crystal, and 9 is a grown single crystal. The starting material 10 is a platinum crucible.
ZnO and V ₂ O ₅ were mixed at a molar ratio of 78:22, and 100 g of the mixture was placed in a platinum crucible 10 also serving as a heating element having a diameter of 45 mm and a height of 30 mm, and induction heating using a high-frequency heating coil 4. After heating to about 1050 ° C. and melting, the ZnO single crystal 7 as a seed crystal is brought into contact with the surface of the melt.
When the temperature of the melt is gradually lowered, ZnO microcrystals are gradually deposited at the interface of the melt in contact with the seed crystal having the lowest temperature in the melt, and crystallize and grow on the seed crystal 7. The single crystal 8 thus grown is gradually pulled up from the melt.
That is, the grown single crystal is simultaneously pulled while the temperature of the melt is lowered. The production conditions at this time are as follows: the rate at which the ZnO single crystal 8 is pulled up is 0.5 to 1.0 mm / h, the rate of cooling the melt is 2 to 10 ° C./h, the number of crystal rotations is 15 to 30 rpm, and the atmosphere is air. Was. A brown ZnO single crystal having a size of 10 × 10 × 4 mm was obtained with a production time of 6 hours.
[0010]
Example 2
Using the same apparatus as in Example 1, a ZnO single crystal was produced by a solution drawing method.
The ZnO and V2O5 and B2O3 in the molar ratio and mixed in 78:11:11, the _Li 2 CO ₃ was added 2g as an impurity, put the mixture 102g in a platinum crucible 10, pulling rate 0.5 as manufacturing conditions 0.0 mm / h, melt cooling rate 2-10 ° C./h, crystal rotation speed 15-30 rpm, atmosphere is air, and a yellow ZnO single crystal having a size of 8 × 8 × 3 mm can be obtained in a manufacturing time of 6 hours. Was.
[0011]
Example 3
Using the same apparatus as in Example 1, a ZnO single crystal was produced by a solution drawing method.
ZnO and B ₂ O ₃ were mixed at a molar ratio of 78:22, 100 g of the mixture was put into a platinum crucible 10, and the production conditions were a pulling rate of 0.5 to 1.0 mm / h and a melt cooling rate of 2 to 10. A slightly brown ZnO single crystal having a size of 10 × 10 × 5 mm was obtained in a temperature of 10 ° C./h, a crystal rotation number of 15 to 30 rpm, and an atmosphere in the atmosphere in a production time of 10 hours.
Since bubbles were observed to emerge from the melt in the above examples, growth was carried out in an oxygen atmosphere, but single crystal growth was possible. No comparison of crystal properties was made.
[0012]
Example 4
A ZnO single crystal was manufactured by a floating zone method.
FIG. 5 shows a floating zone single crystal manufacturing apparatus used. In the figure, 1 is a raw material rod, 2 is a seed crystal, 3 is a melting zone (solvent), 4 and 5 are rotation axes, 6 is a quartz tube, 7 is a halogen lamp, 8 is a spheroid mirror, 9 is an observation window, 10 Denotes a lens, and 11 denotes an observation screen.
The ZnO powder is formed into a round bar having a diameter of 6 mm and a length of 7 cm using a pressure molding machine and is uniformly fired at 1400 ° C. for 15 hours to obtain a ZnO raw material rod 1.
Similarly, a powder obtained by mixing ZnO, V ₂ O _5, and B ₂ O ₃ in a molar ratio of 78:11:11 is fired at 750 ° C for 15 hours, and the powder is shaped into a round bar having a diameter of 6 mm by a pressure molding machine. And then calcined homogeneously at 800 ° C. for 15 hours to obtain a solvent. Thereafter, the columnar rod-shaped solvent is cut in the radial direction to be disc-shaped and fused to the ZnO raw material rod.
The cylindrical rod-shaped sample obtained by fusing the solvent to the tip of the ZnO raw material rod is fixed to the upper sample rotation shaft 4 of the floating zone method single crystal manufacturing apparatus employing the infrared heating method, and the seed is similarly applied to the lower rotation shaft 5. A ZnO firing rod is fixed as the crystal 2.
In this case, the seed crystal 2 and the ZnO raw material rod 1 with the solvent are set so as not to be eccentric with respect to the rotation axis. Then, after the solvent is heated and melted using infrared rays using a halogen lamp 7, the seed crystal is brought into contact with the solvent, and the molten solvent is held between the raw material rod and the seed crystal by the surface tension of the liquid. Thereafter, the raw material rod and the seed crystal are rotated at a speed of 30 rpm in directions opposite to each other.
Further, the molten solvent is moved at a rate of 0.5 mm / hr in the direction of the raw material rod, that is, upward, to grow a ZnO single crystal as a seed crystal. As a result, a cylindrical rod-shaped ZnO crystal having a diameter of 4 mm and a length of 20 mm was obtained.
Since the firing rod was a seed crystal, it was a crystal composed of several grains. The 100 micron diameter in feed rod 1 of the upper shaft are fabricated ZnO acicular crystals of a few millimeters long, maternal and ZnO sintered raw material rod (seed crystal) ZnO and _V 2 _{O 5} and _B 2 _{O 3} as It was also found that if a solution having the composition range claimed in claim 2 was present, needle-like ZnO crystals were produced.
[0013]
[Effects of the present invention]
It was confirmed that the method for producing a ZnO single crystal of the present invention can produce a high-quality single crystal of any size in a desired direction in a short time.
[Brief description of the drawings]
FIG. 1 is a phase diagram of a ZnO—V ₂ O ₅ system. FIG. 2 is a phase diagram of a ZnO—B ₂ O ₃ system. FIG. 3 is a phase diagram of a ZnO—B ₂ O ₃ system. 4) Single crystal pulling device [Fig. 5] is an infrared concentrated heating type single crystal manufacturing device [Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pulling shaft 2 Platinum shaft 3 Insulating agent 4 High frequency heating coil 5 Thermocouple 6 Crucible support 7 Seed crystal 8 Grown single crystal 9 Starting material 10 Platinum crucible

Claims (4)

After mixing and heating and melting the solute, zinc oxide ZnO, and the solvent, vanadium oxide and / or boron oxide, the seed crystal or the substrate is brought into direct contact with the melt to seed the fine crystals of zinc oxide ZnO. A method for producing a ZnO single crystal, wherein the ZnO single crystal is deposited and grown on a crystal or a substrate. The mixing ratio of the zinc oxide ZnO and the solvent vanadium oxide and / or boron oxide is 99.9 to 75 mol% to 0.1 to 25 mol%, and the mixing ratio of the solvent vanadium oxide and boron oxide is 100 to 0 mol%. 2. The method for producing a ZnO single crystal according to claim 1, wherein the amount is from 0 to 100 mol%. The method for producing a ZnO single crystal according to claim 1, wherein the zinc oxide ZnO contains a small amount of a different element. The method for producing a ZnO single crystal according to any one of claims 1 to 3, wherein the different element is one or more elements selected from those forming a solid solution with ZnO within a solid solution limit.

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