Epitaxial growth of nitride compound semiconductor

Details Epitaxial growth of nitride compound semiconductor Epitaxial growth of nitride compound semiconductor

2000-12-29

2002-10-08

Jackson, Jr., Jerome (Department: 2815)

Active solid-state devices (e.g., transistors, solid-state diode

Incoherent light emitter structure

With heterojunction

C257S103000, C257S190000

Reexamination Certificate

active

06462357

ABSTRACT:

FIELD OF THE INVENTION
The present invention provides a III-nitride compound semiconductor device, which is characterized by having a II-nitride compound crystal-island layer in the structure to reduce dislocation of the III-nitride compound occurred during epitaxial growth.
BACKGROUND OF THE INVENTION
III-nitride compound semiconductors, especially semiconductors with GaN-based material are frequently applied to produce light emitting devices such as blue-green light emitting diodes (LED) and laser diodes. These materials usually grow on aluminum oxide (Al
2
O
3
) substrates or silicon carbide (SiC) substrates.
Take the aluminum oxide substrates for example. Because the difference between the lattice constants of Al
2
O
3
substrates and GaN exceeds 16%, a GaN crystal layer is hard to directly grow on an Al
2
O
3
substrate. In U.S. Pat. No. 4,855,249, therefore, Akasaki et al. first disclosed to grow an amorphous AlN buffer layer on an Al
2
O
3
substrate at a low temperature so as to reduce problem caused by the lattice constant difference between an Al
2
O
3
substrate and a GaN layer. Nakamura et al., in U.S. Pat. No. 5,290,393, disclosed to use materials such as GaN or AlGaN to grow as a buffer layer. An amorphous GaN buffer layer was first growing on an Al
2
O
3
substrate at a temperature between 400° C. and 900° C. A GaN epitaxy layer was then growing on the GaN buffer layer at a temperature between 1000° C. and 1200° C. The quality and performance of the GaN epitaxy layer were better than those of a GaN epitaxy layer produced by adopting AlN as a buffer layer.
However, because of dislocation defects caused by the difference between the lattice contants of Al
2
O
3
substrates and GaN materials, even GaN-based, AlGaN-based or AlN-based materials are provided as buffer layer materials, epitaxy layer with GaN-based material still has a dislocation density of 10
10
cm
−2
to 10
8
cm
−2
. This leads to a bad performance of the semiconductor device and affects illumination and electrical property. Thus, methods on how to reduce dislocation density, such as multiple buffer layer structure, epitaxy lateral overgrowth (ELOG) structure, InGaN/GaN superlattice structure, or AlGaN/GaN suprelattice structure, are brought up one after another to reduce dislocation.
SUMMARY OF THE INVENTION
The present invention provides a II-nitride compound material to grow directly on the substrate. This II-nitride compound material grows evenly on the substrate or on the III-nitride compound material with crystal-island structure. The III-nitride compound semiconductor layer is to grow thereon to reduce dislocation of the III-nitride semiconductor layer and improve the epitaxy quality.
The present invention discloses a light emitting device with a single crystal island structure. The materials of the single crystal-island layer are II-nitride compounds, wherein the II-group elements include beryllium (Be), magnesium (Mg), calcium (Ca), strontium (Sr), barium (Ba), zinc (Zn), cadmium (Cd), and mercury (Hg) etc. The single crystal-island layer grows on the substrate with a certain distance between each two of the single crystal islands. III-nitride compound semiconductor layer then grows on the single crystal-island layer. Because III-nitride compound semiconductor layer grows along II-nitride compound single crystal islands, dislocation occurred during epitaxy is to be confined to where II-nitride compound single crystal island is. Hence, dislocation density is to be reduced effectively.


REFERENCES:
patent: 6261931 (2001-07-01), Keller

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