Method of manufacturing GaN ingots

Details Method of manufacturing GaN ingots Method of manufacturing GaN ingots

2000-06-02

2003-05-13

Kunemund, Robert (Department: 1765)

Single-crystal, oriented-crystal, and epitaxy growth processes;

Processes of growth from liquid or supercritical state

Having pulling during growth

C117S013000, C117S062000, C117S103000, C117S108000, C117S952000

Reexamination Certificate

active

06562124

ABSTRACT:

FELD OF THE INVENTION
The present invention relates to the growth of bulk semiconductor materials in a manner which provides a possibility to manufacture bulk crystals in the form of ingots, fabricate substrates from these ingots and thus enhancing the resulting performance of devices made from those semiconductors. In particular, the invention relates to the method of growing gallium nitride (GaN) ingots and epitaxial layers from the melt-solutions.
BACKGROUND OF THE INVENTION
Resent results in fabrication of GaN-based light-emitting diodes (LEDs) and laser diodes (LDs) operating in green, blue, and ultra violet spectrum region have demonstrated tremendous commercial potential of nitride semiconductors. Because of lack of GaN substrates, these devices have been developed on the sapphire or silicon carbide substrates and are suffering from high defect density in the device structures including high density of threading dislocations, up to 10
10
cm
−2
, domains and grain boundaries. Destructive influence of these imperfections on the device performance has been demonstrated in a number of publications. Recently, in S. Nakamura, M. Senoh, S. Nagahama, N. Iwasa, T. Yamada, T. Matsushita, H. Kiyouku, Y. Sugimoto, T. Kozaki, H. Umemoto, M. Sano, and K. Chocho,
Applied Physics Letters, Vol
. 72, p. 2014 (1998), the fabrication of LDs on free-standing reduced-defect-density 80 &mgr;m thick GaN substrate grown by hydride vapor phase epitaxy with lifetime longer than 780 hr. and threshold current density of 7 kA/cm
2
was reported. In contrast, the LDs fabricated under similar conditions but on a sapphire substrate exhibited shorter lifetime of 200 hr at lower operating current density.
The fact that misfit dislocations, grain boundaries, domains and residual stresses greatly reduce performance of GaN-based devices and cut their applications was experimentally proven. The main issue in GaN-based technology is lack of GaN and AlN substrates.
Foreign substrates including Al
2
O
3
, SiC, ZnO, LiGaO
2
, LiAlO
2
, and ScMgAlO
4
have been tested for GaN heteroepitaxial growth. Lattice and thermal mismatch between foreign substrate and grown GaN-based device structure originate most of the defects. It is clear that only GaN substrates will allow one to reduce defect density in GaN devices and improve device characteristics.
The main challenge in growing GaN substrates is incongruent decomposition of GaN material by sublimation that becomes noticeable at temperatures from 800-1100° C. A number of attempts to realize growth of bulk and quasi-bulk GaN crystals from vapor phase have been done. Natural ways to overcome the decomposition problem are (1) to use the chemical transport technique or (2) sublimation growth at high pressure. Both methods have been applied to grow GaN layers but due to technological difficulties no GaN ingots were grown. In these methods, thick GaN layers were grown on foreign substrates and had high defect density.
Another method to grow GaN crystals is the growth from liquid phase. The main problem in liquid phase growth of GaN from liquid phase is extremely low solubility of nitrogen in melts, particularly in Ga melt. GaN crystals having area up to 200 mm
2
and thickness up to 0.2 mm were grown by melt-solution technique (S. Porowski,
Proceedings of the Second International Conference on Nitride Semiconductors ICNS
'97, Tokushima, Japan, Oct. 27-31, 1997, p. 430). These GaN crystals were spontaneously nucleated and grown from nitrogen-gallium melt-solution. In order to overcome low nitrogen solubility problem, growth temperatures from 1500-1600° C. and nitrogen gas pressure from 10-20 kbar are required to grow GaN crystals. Even at these high pressures and temperatures nitrogen solubility in gallium melt is very low. As a result, at 20,000 bar and 1500° C. growth rate of about 0.01-0.05 mm/hr can be obtained. Lateral growth rate (growth rate perpendicular to [0001] crystallographic direction) was about 1 mm/day. Undoped GaN crystals grown by this method have high background electron concentration and did not exhibit edge luminescence under optical excitation. GaN ingots were not grown by this technique.
Another attempt to grow GaN crystal from Ga—N melt-solution was undertaken by Takayuki Inoue, Yoji Seki, Osamu Oda, Satoshi Kurai, Yoichi Yamada and Tsunemasa Taguchi,
Jpn. J. Appl. Phys. Vol
. 39 (2000) pp. 2394-2398. GaN crystals up to 10 mm in diameter were grown at 1475° C. under a nitrogen pressure of 0.98 GPa. High pressure in combination with high temperature required for both above methods make it difficult to perform controllable GaN crystal growth using GaN seed and develop these methods as production techniques.
One way to increase nitrogen solubility is to use not pure Ga melt but Ga with some additives. Alternative melts were used in D. Elwell, R. S. Feigelson, M. M. Simkins, and W. A. Tiller,
Journal of Crystal Growth, Vol
. 66, p. 45 (1984). Growth was carried out in the temperature range from 900 and 1000° C. A sapphire wafer used as substrate was placed in either end of the furnace and the boat was charged with 50 g of 99.9999% pure gallium, Ga/Bi and Ga/Sn alloys. Ammonia gas served as nitrogen source. Ammonia partial pressure was (1.5-2)×10
−3
bar. As carrier gas hydrogen or argon were used. In some experiments, GaN seeds were employed. The growth reaction proceeded for 10 days. The GaN deposition was in the form of small crystallites randomly oriented with respect to the seed crystals. The largest crystal grown, of 2.5 mm in length, was part of a cluster of three crystals grown at 930° C. on SiC plate with ammonia partial pressure of 1.08×10
−3
bar. The use of seed crystals appeared to have no beneficial effect on crystal size. The addition of Bi to the solution was found to increase the number of crystallites nucleated. Tin was tried as an alternative solvent component. The major advantage of tin is that it reacts with nitrogen giving atomic nitrogen in solution. It was therefore considered possible that the solubility of atomic nitrogen in molten Ga/Sn alloy would be higher than that in Ga melt. Alloys with 10-80 at. % content of Sn were tested. Nitrogen gas was used in place of the NH
3
+H
2
mixture with a slow growth rate of about 150 cm
3
/day. Some GaN growth was observed, together with oxide impurities. But, in all these experiments the crystallites were smaller than pure gallium was used. GaN ingots were not grown by this technique.
Alternative way to introduce nitrogen in Ga melt to grow polycrystalline GaN was described in A. Argoitia, C. C. Hayman, J. C. Angus, L. Wang, J. S. Dyck, and K. Kash,
Applied Physics Letters, Vol
. 70, p. 179 (1997). Plasma gun was used to increase the thermodynamic activity of the nitrogen in order to raise the nitrogen concentration in the gallium. The active species in the plasma include N, N
+
, N
2
+
, and excited states of N
2
. Recombination of N to form N
2
is strongly favored thermodynamically, however, this recombination is sufficiently slow within the gallium melt to permit the parallel formation of GaN. Synthesis of GaN was achieved by directing plasma from electron cyclotron resonance microwave source (ECR-source) onto a liquid Ga pool heated of up to 1000° C. in BN crucible. The ECR source was mounted directly above the crucible and gave an ion flux density of 10
16
cm
−2
sec
−1
. The partial pressure of atomic nitrogen in the beam is approximately 0.05 mTorr. An argon plasma was employed for 10 min followed by a hydrogen plasma for 30 min to clean melt surface. The hydrogen flow was replaced by 10 sccm of nitrogen and the temperature raised slowly to 1000° C. During this step, the pressure was fixed at 0.5 mTorr. After 15 min., at a temperature of 700° C., the growth of a crust of polycrystalline GaN began on the melt surface. The nitrogen plasma was maintained for 12 hr at the final temperature of 1000° C. At the end of a run, a polycrystalline GaN “dome” completely covered the Ga melt. A typical “dome” was 0.1 m

Affiliated with

Also associated with

Rating

Method of manufacturing GaN ingots does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of manufacturing GaN ingots, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of manufacturing GaN ingots will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3016121