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Gallium nitride bulk crystals and their growth method 実績あり

外国特許コード F110003790
整理番号 E06742US1
掲載日 2011年7月5日
出願国 アメリカ合衆国
出願番号 23424408
公報番号 20090072352
公報番号 8253221
出願日 平成20年9月19日(2008.9.19)
公報発行日 平成21年3月19日(2009.3.19)
公報発行日 平成24年8月28日(2012.8.28)
優先権データ
  • 60/973,662P (2007.9.19) US
発明の名称 (英語) Gallium nitride bulk crystals and their growth method 実績あり
発明の概要(英語) A gallium nitride crystal with a polyhedron shape having exposed {10-10} m-planes and an exposed (000-1) N-polar c-plane, wherein a surface area of the exposed (000-1) N-polar c-plane is more than 10 mm2 and a total surface area of the exposed {10-10} m-planes is larger than half of the surface area of (000-1) N-polar c-plane.
The GaN bulk crystals were grown by an ammonothermal method with a higher temperature and temperature difference than is used conventionally, and using an autoclave having a high-pressure vessel with an upper region and a lower region.
The temperature of the lower region of the high-pressure vessel is at or above 550° C., the temperature of the upper region of the high-pressure vessel is set at or above 500° C., and the temperature difference between the lower and upper regions is maintained at or above 30° C.
GaN seed crystals having a longest dimension along the c-axis and exposed large area m-planes are used.
従来技術、競合技術の概要(英語) BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to gallium nitride bulk crystals and methods for making the same.
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., [Ref. 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.)
The usefulness of gallium nitride (GaN), and its ternary and quaternary alloys incorporating aluminum and indium (AlGaN, InGaN, AlInGaN), has been well established for fabrication of visible and ultraviolet optoelectronic devices and high-power electronic devices.
These devices are typically grown epitaxially on heterogeneous substrates, such as sapphire and silicon carbide, since GaN wafers are very expensive.
The heteroepitaxial growth of group III-nitride causes highly defected or even cracked films, which deteriorate the performance and reliability of these devices.
In order to eliminate the problems arising from the heteroepitaxial growth, GaN wafers sliced from bulk GaN crystals must be used.
However, it is very difficult to grow a bulk crystal of GaN, since GaN has a high melting point and high nitrogen vapor pressure at high temperature.
Up to now, a few methods such as high-pressure high-temperature synthesis [Ref. 1, 2] and a sodium flux method [Ref. 3, 4] have been used to obtain bulk group III-nitride crystals.
However, the crystal shape obtained by these methods is a thin platelet because these methods are based on a Ga melt, in which nitrogen has very low solubility and a low diffusion coefficient.
A new technique is based on supercritical ammonia, which has high solubility of source materials, such as polycrystalline GaN or Ga metal, and which has high transport speed of dissolved precursors.
This ammonothermal method [Ref. 5-9] has a potential for growing large GaN crystals.
However, existing technology is limited by the crystal size, because the growth rate is not fast enough to obtain large crystals.

特許請求の範囲(英語) [claim1]
1. A gallium nitride crystal having a polyhedron shape with exposed {10-10} m-planes and an exposed (000-1) N-polar c-plane, wherein a surface area of the exposed (000-1) N-polar c-plane is more than 10 mm2 and a total surface area of the exposed {10-10} m-planes is larger than half of the surface area of the exposed (000-1) N-polar c-plane.
[claim2]
2. The gallium nitride crystal of claim 1, wherein the crystal is grown in supercritical ammonia.
[claim3]
3. The gallium nitride crystal of claim 2, wherein the crystal is grown on a seed crystal and the seed crystal is an a-plane oriented gallium nitride wafer.
[claim4]
4. The gallium nitride crystal of claim 3, wherein the a-plane oriented seed crystal is obtained by slicing a GaN boule grown by an ammonothermal method.
[claim5]
5. The gallium nitride crystal of claim 2, wherein the crystal is grown on a seed crystal and the seed crystal is an m-plane oriented gallium nitride wafer.
[claim6]
6. The gallium nitride crystal of claim 2, wherein the crystal is grown on a seed crystal and the seed crystal is a c-plane oriented gallium nitride wafer.
[claim7]
7. The gallium nitride crystal of claim 2, wherein the crystal is grown on a rod-shaped gallium nitride crystal having its longest dimension along a c-axis.
[claim8]
8. A gallium nitride wafer sliced from the crystal of claim 1.
[claim9]
9. A method for growing gallium nitride (GaN) crystals in a high-pressure vessel, comprising: heating a lower region of an inner room in the high-pressure vessel at or above 550 deg. C., and heating an upper region of the inner room at or above 500 deg. C., while maintaining a temperature difference between the lower region and upper region at or above 30 deg. C.,
wherein the gallium nitride (GaN) crystals have exposed {10-10} m-planes and an exposed (000-1) N-polar c-plane, and a surface area of the exposed (000-1) N-polar c-plane is more than 10 mm2, and a total surface area of the exposed {10--10} m-planes is larger than half of the surface area of the exposed (000-1) N-polar c-plane.
[claim10]
10. The method of claim 9, further comprising: (a) loading alkali-based mineralizers at a bottom of a high-pressure vessel, GaN single crystalline seeds in the lower region of the high-pressure vessel, and Ga-containing materials in the upper region of the high pressure vessel;
(b) filling the high-pressure vessel with ammonia;
(c) sealing the high-pressure vessel;
(d) heating the lower region of the high-pressure vessel with an external heater at or above 550 deg. C., heating the upper region of the high-pressure vessel with external heat at or above 500 deg. C., while maintaining the temperature difference between the lower region and upper region at or above 30 deg. C.;
(e) holding the lower region at or above at or above 550 deg. C., holding the upper region at or above 500 deg. C., and maintaining the temperature difference, for more than 30 days;
(f) releasing high-pressure ammonia at a temperature higher than 300 deg. C.;
(g) unsealing the high-pressure vessel at a temperature higher than 300 deg. C.; and
(h) cooling down the high-pressure vessel; and
(i) wherein the high-pressure vessel is made of a Ni -- Cr based alloy, has a longest dimension along a vertical direction, and has flow-restricting plates to divide an inner room of the high-pressure vessel into the upper region and the lower region.
[claim11]
11. The method of claim 10, wherein the GaN single crystalline seeds have a-plane orientation and are sliced from a GaN crystal grown by an ammonothermal method.
[claim12]
12. A gallium nitride (GaN) crystal having a polyhedron shape with exposed {10--10} m-planes and an exposed (000-1) N-polar c-plane grown by a method comprising: (a) loading alkali-based mineralizers at a bottom of a high-pressure vessel, GaN single crystalline seeds in the lower region of the high-pressure vessel, and Ga-containing materials in the upper region of the high pressure vessel;
(b) filling the high-pressure vessel with ammonia;
(c) sealing the high-pressure vessel;
(d) heating the lower region of the high-pressure vessel with an external heater at or above 550 deg. C., heating the upper region of the high-pressure vessel with external heat at or above 500 deg. C., while maintaining the temperature difference between the lower region and upper region at or above 30 deg. C.;
(e) holding the lower region at or above at or above 550 deg. C., holding the upper region at or above 500 deg. C., and maintaining the temperature difference, for more than 30 days;
(f) releasing high-pressure ammonia at a temperature higher than 300 deg. C.;
(g) unsealing the high-pressure vessel at a temperature higher than 300 deg. C.; and
(h) cooling down the high-pressure vessel; and
(i) wherein the high-pressure vessel is made of a Ni -- Cr based alloy, has a longest dimension along a vertical direction, and has flow-restricting plates to divide an inner room of the high-pressure vessel into the upper region and the lower region,
(j) wherein a surface area of the exposed (000-1) N-polar c-plane is more than 10 mm2, and a total surface area of the exposed {10--10} m-planes is larger than half of the surface area of the exposed (000-1) N-polar c-plane.
[claim13]
13. The GaN crystal of claim 12, wherein the GaN single crystalline seeds have a-plane orientation and are sliced from a GaN crystal grown by an ammonothermal method.
  • 発明者/出願人(英語)
  • HASHIMOTO TADAO
  • NAKAMURA SHUJI
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
国際特許分類(IPC)
米国特許分類/主・副
  • 257/615
  • 257/E21.697
  • 423/409
  • 438/604
参考情報 (研究プロジェクト等) ERATO NAKAMURA Inhomogeneous Crystal AREA
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