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Technique for the growth of planar semi-polar gallium nitride 実績あり

外国特許コード F110003762
整理番号 E06712US1
掲載日 2011年7月4日
出願国 アメリカ合衆国
出願番号 37291406
公報番号 20060205199
公報番号 7220324
出願日 平成18年3月10日(2006.3.10)
公報発行日 平成18年9月14日(2006.9.14)
公報発行日 平成19年5月22日(2007.5.22)
優先権データ
  • 60/660,283P (2005.3.10) US
発明の名称 (英語) Technique for the growth of planar semi-polar gallium nitride 実績あり
発明の概要(英語) A method for growing planar, semi-polar nitride film on a miscut spinel substrate, in which a large area of the planar, semi-polar nitride film is parallel to the substrate's surface.
The planar films and substrates are: (1) {10 <O OSTYLE="SINGLE">11} gallium nitride (GaN) grown on a {100} spinel substrate miscut in specific directions, (2) {10 <O OSTYLE="SINGLE">13} gallium nitride (GaN) grown on a {110} spinel substrate, (3) {11 <O OSTYLE="SINGLE">22} gallium nitride (GaN) grown on a {1 <O OSTYLE="SINGLE">100} sapphire substrate, and (4) {10 <O OSTYLE="SINGLE">13} gallium nitride (GaN) grown on a {1 <O OSTYLE="SINGLE">100} sapphire substrate.
従来技術、競合技術の概要(英語) BACKGROUND OF THE INVENTION
1.
Field of the Invention.
The present invention relates to a technique for the growth of planar semi-polar gallium nitride.
2. Description of the Related Art.
The usefulness of gallium nitride (GaN), and its ternary and quaternary compounds 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 using growth techniques including molecular beam epitaxy (MBE), metalorganic chemical vapor deposition (MOCVD), and hydride vapor phase epitaxy (HVPE).
GaN and its alloys are most stable in the hexagonal würtzite crystal structure, in which the structure is described by two (or three) equivalent basal plane axes that are rotated 1200 with respect to each other (the a-axes), all of which are perpendicular to a unique c-axis.
Group III and nitrogen atoms occupy alternating c-planes along the crystal's c-axis.
The symmetry elements included in the wurtzite structure dictate that III-nitrides possess a bulk spontaneous polarization along this c-axis, and the würtzite structure exhibits piezoelectric polarization.
Current nitride technology for electronic and optoelectronic devices employs nitride films grown along the polar c-direction.
However, conventional c-plane quantum well structures in III-nitride based optoelectronic and electronic devices suffer from the undesirable quantum-confined Stark effect (QCSE), due to the existence of strong piezoelectric and spontaneous polarizations.
The strong built-in electric fields along the c-direction cause spatial separation of electrons and holes that in turn give rise to restricted carrier recombination efficiency, reduced oscillator strength, and red-shifted emission.
One approach to eliminating the spontaneous and piezoelectricpolarization effects in GaN optoelectronic devices is to grow the devices on non-polar planes of the crystal.
Such planes contain equal numbers of Ga and N atoms and are charge-neutral.
Furthermore, subsequent non-polar layers are equivalent to one another so the bulk crystal will not be polarized along the growth direction.
Two such families of symmetry-equivalent non-polar planes in GaN are the {11 20} family, known collectively as a-planes, and the {1 100} family, known collectively as m-planes.
Unfortunately, despite advances made by researchers at the University of California, for example, as described in the applications cross-referenced above, growth of non-polar GaN remains challenging and has not yet been widely adopted in the III-nitride industry.
Another approach to reducing or possibly eliminating the polarization effects in GaN optoelectronic devices is to grow the devices on semi-polar planes of the crystal.
The term "semi-polar planes" can be used to refer to a wide variety of planes that possess both two nonzero h, i, or k Miller indices and a nonzero 1 Miller index.
Some commonly observed examples of semi-polar planes in c-plane GaN heteroepitaxy include the {11 22}, {10 11}, and {10 13} planes, which are found in the facets of pits.
These planes also happen to be the same planes that the inventors have grown in the form of planar films.
Other examples of semi-polar planes in the würtzite crystal structure include, but are not limited to, {10 12}, {20 21}, and {10 14}. The nitride crystal's polarization vector lies neither within such planes or normal to such planes, but rather lies at some angle inclined relative to the plane's surface normal.
For example, the {10 11} and {10 13} planes are at 62.98 deg. and 32.06 deg. to the c-plane, respectively.
The other cause of polarization is piezoelectric polarization.
This occurs when the material experiences a compressive or tensile strain, as can occur when (Al, In, Ga, B)N layers of dissimilar composition (and therefore different lattice constants) are grown in a nitride heterostructure.
For example, a thin AlGaN layer on a GaN template will have in-plane tensile strain, and a thin InGaN layer on a GaN template will have in-plane compressive strain, both due to lattice matching to the GaN.
Therefore, for an InGaN quantum well on GaN, the piezoelectric polarization will point in the opposite direction than that of the spontaneous polarization of the InGaN and GaN.
For an AlGaN layer latticed matched to GaN, the piezoelectric polarization will point in the same direction as that of the spontaneous polarization of the AlGaN and GaN.
The advantage of using semi-polar planes over c-plane nitrides is that the total polarization will be reduced.
There may even be zero polarization for specific alloy compositions on specific planes.
Such scenarios will be discussed in detail in future scientific papers.
The important point is that the polarization will be reduced compared to that of c-plane nitride structures.
Bulk crystals of GaN are not available, so it is not possible to simply cut a crystal to present a surface for subsequent device regrowth.
Commonly, GaN films are initially grown heteroepitaxially, i.e. on foreign substrates that provide a reasonable lattice match to GaN.
Semi-polar GaN planes have been demonstrated on the sidewalls of patterned c-plane oriented stripes.
Nishizuka et al. have grown {11 22} InGaN quantum wells by this technique. (See Nishizuka, K., Applied Physics Letters, Vol. 85, No. 15, 11 Oct. 2004.) They have also demonstrated that the internal quantum efficiency of the semi-polar plane {11 22} is higher than that of the c-plane, which results from the reduced polarization.
However, this method of producing semi-polar planes is drastically different than that of the present invention; it is an artifact from epitaxial lateral overgrowth (ELO).
ELO is used to reduce defects in GaN and other semiconductors.
It involves patterning stripes of a mask material, often SiO2 for GaN.
The GaN is grown from open windows between the mask and then grown over the mask.
To form a continuous film, the GaN is then coalesced by lateral growth.
The facets of these stripes can be controlled by the growth parameters.
If the growth is stopped before the stripes coalesce, then a small area of semi-polar plane can be exposed.
The surface area may be 10 mu m wide at best.
Moreover, the semi-polar plane will be not parallel to the substrate surface.
In addition, the surface area is too small to process into a semi-polar LED.
Furthermore, forming device structures on inclined facets is significantly more difficult than forming those structures on normal planes.
The present invention describes a technique for the growth of planar films of semi-polar nitrides, in which a large area of (Al, In, Ga)N is parallel to the substrate surface.
For example, samples are often grown on 10 mm * 10 mm or 2 inch diameter substrates compared to the few micrometer wide areas previously demonstrated for the growth of semi-polar nitrides.

特許請求の範囲(英語) [claim1]
1. A method for growing a nitride film, comprising: growing a planar, semi-polar nitride film on a substrate, wherein the planar, semi-polar nitride film is grown parallel to the substrate's surface.
[claim2]
2. The method of claim 1, wherein a surface area of the planar, semi-polar nitride film of at least 10 mm * 10 mm is parallel to the substrate's surface.
[claim3]
3. The method of claim 1, wherein a surface area of the planar, semi-polar nitride film having at least a 2 inch diameter is parallel to the substrate's surface.
[claim4]
4. The method of claim 1, wherein the planar, semi-polar nitride film is {10 11} gallium nitride (GaN) grown on a {100} spinel substrate miscut in specific directions.
[claim5]
5. The method of claim 4, wherein the specific directions comprise <001>, <010> and <011>.
[claim6]
6. The method of claim 1, wherein the planar, semi-polar nitride film is {10 11} AlN, InN, AlGaN, InGaN, or AlInN grown on a (100) spinel substrate miscut in specific directions.
[claim7]
7. The method of claim 6, wherein the specific directions comprise <001>, <010> and <011>.
[claim8]
8. The method of claim 1, wherein the planar, semi-polar nitride film is {10 13} gallium nitride (GaN) grown on a {110} spinel substrate.
[claim9]
9. The method of claim 1, wherein the planar, semi-polar nitride film is {11 22} gallium nitride (GaN) grown on a {1 100} sapphire substrate.
[claim10]
10. The method of claim 1, wherein the planar, semi-polar nitride film is {10 13} gallium nitride (GaN) grown on a {1 100} sapphire substrate.
[claim11]
11. The method of claim 1, further comprising the steps of: loading the substrate into a reactor, wherein the reactor is evacuated to remove oxygen, and then backfilled with nitrogen;
turning on a furnace and ramping a temperature of the reactor under conditions that encourage nitridization of the substrate's surface;performing a gas flow of nitrogen, hydrogen, or ammonia over the substrate at atmospheric pressure;reducing the reactor's pressure when the furnace reaches a setpoint temperature;performing a gallium nitride (GaN) growth on the substrate, after the reactor's pressure is reduced, by flowing ammonia, and initiating a flow of hydrogen chloride (HCl) over gallium (Ga) to start the growth of the GaN;
and
cooling down the reactor after the growth of the GaN, wherein the HCl flow is stopped, and the reactor is cooled down while flowing ammonia to preserve the GaN.
[claim12]
12. The method of claim 11, wherein the substrate is miscut before being loaded into the reactor.
[claim13]
13. The method of claim 11, wherein, for growth of {11 22} GaN, ammonia is flowed while the furnace is ramping to the growth temperature, so that nitridation occurs at low temperature.
[claim14]
14. The method of claim 11, wherein, for growth of {10 13} GaN, only hydrogen and nitrogen are flowed during the temperature ramping step, and the substrate is then subjected to a high temperature nitridation with ammonia flow at the growth temperature.
[claim15]
15. The method of claim 1, further comprising, after the planar, semi-polar nitride film has been grown, growing one or more device layers on the on the planar, semi-polar nitride film.
[claim16]
16. The method of claim 15, wherein the step of growing the device layers on the planar, semi-polar nitride film includes doping the device layers with n-type and p-type dopants, and growing one or more quantum wells in a regrowth layer.
[claim17]
17. The method of claim 16, further comprising fabricating a light emitting diode from the device layers.
[claim18]
18. A planar, semi-polar nitride film grown using the method of claim 1.
  • 発明者/出願人(英語)
  • BAKER TROY J
  • HASKELL BENJAMIN A
  • FINI PAUL T
  • DENBAARS STEVEN P
  • SPECK JAMES S
  • NAKAMURA SHUJI
  • JAPAN SCIENCE AND TECHNOLOGY AGENCY
国際特許分類(IPC)
米国特許分類/主・副
  • 148/33
  • 257/E21.113
  • 257/E21.121
  • 257/E21.463
  • 438/46
  • 438/47
  • 438/479
参考情報 (研究プロジェクト等) ERATO NAKAMURA Inhomogeneous Crystal AREA
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