MOCVD Growth of Epitaxial GaN on Lattice-Matched Substrates

The III-V nitride semiconductor family affords many unique properties which make these materials attractive candidates for producing electronic and optoelectronic devices. Much progress has been made in epitaxial thin film growth of nitrides using metalorganic chemical vapor deposition (MOCVD) and molecular beam epitaxy (MBE) during the last decade. These efforts are hindered by the lack of lattice-matched substrates. Most studies have employed sapphire substrates for GaN although there is a large mismatch between these materials. GaN films on sapphire substrates have a great number of threading dislocations which propagate up to the surface. Such highly defective material suffers both from low carrier mobilities and lifetimes. Although low temperature, pulsed laser operation has been achieved, the defects may also act as optical scattering centers, preventing the demonstration of a low threshold CW injection lasers operating at room temperature. Recently, LiAl02 and lithium gallate, substrates with improved lattice matching to GaN, have been developed. In preliminary experiments, GaN grown on LAO by ECR MBE at 800 C, exhibited optically pumped stimulated emission. However, MBE is not suitable for production applications and, in addition, LAO and LGO cannot withstand the high temperatures used in conventional MOCVD. NZ Applied Technologies has achieved promising results for GaN growth at low substrate temperatures using a novel MOCVD-based growth process. This approach can yield high quality GaN on LAO or LGO substrates at substrate temperatures which are compatible with these new materials. This would represent the first successful use of MOCVD with LAO or LGO and would pave the way for their use in a manufacturable process for optoelectronic devices.