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Method for growing group III-nitride crystals in a mixture of supercritical ammonia and nitrogen, and group III-nitride crystals grown thereby 実績あり

外国特許コード F110003791
整理番号 E06744US1
掲載日 2011年7月5日
出願国 アメリカ合衆国
出願番号 97766107
公報番号 20080102016
公報番号 7803344
出願日 平成19年10月25日(2007.10.25)
公報発行日 平成20年5月1日(2008.5.1)
公報発行日 平成22年9月28日(2010.9.28)
優先権データ
  • 60/854,567P (2006.10.25) US
発明の名称 (英語) Method for growing group III-nitride crystals in a mixture of supercritical ammonia and nitrogen, and group III-nitride crystals grown thereby 実績あり
発明の概要(英語) A method of growing group III-nitride crystals in a mixture of supercritical ammonia and nitrogen, and the group-III crystals grown by this method.
The group III-nitride crystal is grown in a reaction vessel in supercritical ammonia using a source material or nutrient that is polycrystalline group III-nitride, amorphous group III-nitride, group-III metal or a mixture of the above, and a seed crystal that is a group-III nitride single crystal.
In order to grow high-quality group III-nitride crystals, the crystallization temperature is set at 550° C. or higher.
Theoretical calculations show that dissociation of NH3 at this temperature is significant.
However, the dissociation of NH3 is avoided by adding extra N2 pressure after filling the reaction vessel with NH3.
従来技術、競合技術の概要(英語) BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention is related to a method for growing group III-nitride crystals in a mixture of supercritical ammonia and nitrogen, and group III-nitride crystals grown by the method.
2. Description of the Related Art
(Note: This application references a number of different publications as indicated throughout the specification by one or more reference numbers within brackets, e.g., [x].
A list of these different publications ordered according to these reference numbers can be found below in the section entitled "References." Each of these publications is incorporated by reference herein.)
Gallium nitride (GaN), and its ternary and quaternary alloys containing aluminum and indium (AlGaN, InGaN, AlInGaN), has been used in wide variety of light emitting devices and electronic devices, such as light emitting diodes (LEDs), laser diodes (LDs), microwave power transistors, and solar-blind photo detectors.
Some of these devices are already in the market, and widely used in cell phones, indicators, displays, etc.
However, these devices are typically grown epitaxially on heterogeneous substrates, such as sapphire and silicon carbide since GaN wafers are not yet available.
The heteroepitaxial growth of group III-nitride causes highly defected or even cracked films, which hinders the realization of high-end optical and electronic devices, such as high-brightness LEDs for general lighting and blue LDs for DVD recording.
All the problems related to heteroepitaxial growth of group III-nitride can be ultimately solved by using group III-nitride single crystalline wafers, which are sliced from bulk group III-nitride crystal ingots.
However, it is very difficult to grow a bulk crystal of group III-nitride, such as GaN, AlN, and InN, since group III-nitride has a high melting point and high nitrogen vapor pressure at high temperature.
Up to now, a couple of growth methods using molten Ga, such as high-pressure high-temperature synthesis [1,2] and sodium flux [3,4], have been used to obtain bulk group III-nitride crystals.
However, the crystal shape grown in molten Ga becomes a thin platelet because molten Ga has low solubility of nitrogen and a low diffusion coefficient of nitrogen.
On the other hand, growth of group III-nitride crystals in supercritical ammonia has been proposed and researched by several groups [5-10].
This new technique called ammonothermal growth has the potential for growing large bulk group III-nitride crystals, because supercritical ammonia used as a fluid medium has high solubility of source materials, such as group III-nitride polycrystals or group III metal, and has high transport speed of dissolved precursors.
However, state-of-the-art ammonothermal method is limited by the growth rate of the group III-nitride crystal, which impedes the application of this method to industrial mass production.
The present invention discloses new findings that are derived by theoretical calculations of the equilibrium molar ratio of NH3, N2, and H2 in the ammonothermal reaction.
The new findings from these calculations reveal the weak point of the current ammonothermal method.
Based on these new findings, a new approach to solving the growth rate problem of the ammonothermal method is disclosed.

特許請求の範囲(英語) [claim1]
1. An ammonothermal method for growing group III-nitride crystals, comprising: (a) loading group III-containing source materials, group III-nitride seed crystals, and mineralizers into a reaction vessel;
(b) filling the reaction vessel with ammonia;
(c) adding extra nitrogen (N2) pressure in the reaction vessel to avoid disassociation of the ammonia into N2 and H2;
(d) raising the reaction vessel's temperature to attain a supercritical state for the ammonia; and
(e) ammonothermally growing the group III-nitride crystals, wherein convection of the supercritical ammonia transfers the source materials and deposits the transferred source materials onto the seed crystals.
[claim2]
2. The method of claim 1, wherein the extra nitrogen (N2) pressure in the adding step (c) is more than 100 atm.
[claim3]
3. The method of claim 2, wherein the group III-containing source materials are either metallic Ga, polycrystalline GaN, amorphous GaN or a mixture thereof, and the group III-nitride seed crystals are GaN.
[claim4]
4. The method of claim 3, wherein the reaction vessel is divided into a dissolution region and a crystallization region with a convection-restricting device, the group III-containing source materials are placed in a dissolution region, the group III-nitride seed crystals are placed in the crystallization region, and the crystallization region's temperature is maintained at 550 deg. C. or higher.
[claim5]
5. The method of claim 4, wherein the mineralizers contain at least one substance selected from LiNH2, NaNH2, and KNH2, and the dissolution region's temperature is maintained lower than the crystallization region's temperature.
[claim6]
6. The method of claim 5, wherein an inner surface of the reaction vessel is protected with a liner material containing vanadium.
[claim7]
7. The method of claim 4, wherein the mineralizers contain at least one substance selected from NH4F, NH4Cl, NH4Br, and NH4I, and the dissolution region's temperature is maintained higher than the crystallization region's temperature.
[claim8]
8. The method of claim 7, wherein an inner surface of the reaction vessel is protected with a liner material containing platinum or palladium.
[claim9]
9. The method of claim 4, wherein the group III-containing source materials contain metallic Ga and the method further comprises transforming the metallic Ga into a substance that contains Ga and N.
[claim10]
10. The method of claim 9, wherein the transforming step further comprises holding the reaction vessel's temperature lower than 300 deg. C. for more than 1 hour before raising the reaction vessel's temperature for crystal growth.
[claim11]
11. The method of claim 10, wherein the mineralizers contain at least one substance selected from LiNH2, NaNH2, and KNH2, and the dissolution region's temperature is maintained lower than the crystallization region's temperature.
[claim12]
12. The method of claim 11, wherein an inner surface of the reaction vessel is protected with a liner material containing vanadium.
[claim13]
13. The method of claim 10, wherein the mineralizers contain at least one substance selected from NH4F, NH4Cl, NH4Br, and NH4I, and the dissolution region's temperature is maintained higher than the crystallization region's temperature.
[claim14]
14. The method of claim 13, wherein an inner surface of the reaction vessel is protected with a liner material containing platinum or palladium.
[claim15]
15. A group III-nitride crystal grown by the method of claim 1.
[claim16]
16. The group III-nitride crystal of claim 15, further comprising a single crystalline group III-nitride crystal.
[claim17]
17. The group III-nitride crystal of claim 16, further comprising a single crystalline group III-nitride wafer sliced from the single crystalline group III-nitride crystal.
[claim18]
18. The group III-nitride crystal of claim 15, wherein the group III-nitride crystal is a gallium nitride crystal.
  • 発明者/出願人(英語)
  • HASHIMOTO TADAO
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
国際特許分類(IPC)
米国特許分類/主・副
  • 423/409
  • 423/111
参考情報 (研究プロジェクト等) ERATO NAKAMURA Inhomogeneous Crystal AREA
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