ABSTRACT
GaN based nitride semiconductors can be grown epitaxially over a number of substrates including 3" diameter sapphire, thus monocrystalline layers can be obtained over large areas. Alloys of GaN with InN and AIN can be prepared covering the spectral range from red to vacuum UV (1.9 to 6.2 eV). The quaternary system InGaAIN has the potential for achieving lattice-matched double heterojunctions throughout the entire layered structure. The most studied compound of this system is GaN. Despite their use in GaN to form ternary alloys in many device structures, AIN and InN are still much less understood compared to GaN, and their technology is much less advanced. Remarkable progress in the growth of high quality epitaxial Ill-nitride films by a variety of methods such as Vapor Phase Epitaxy (VPE) [1], Reactive Molecular Beam Epitaxy (MBE) [2-4] and bulk crystal growth from Ga solution have recently been achieved. By far the most frequently
used methods are the VPE methods. The most successful among the VPE methods is the metalorganic chemical vapor deposition (MOCVD). MOCVD growth produces the best quality layers suitable for GaN based optoelectronic devices, LED’s and lasers, albeit the quality of MBE films comes close to that grown by MOCVD. The inorganic VPE was the first method used to grow epitaxial III-N semiconductors, but it was nearly abandoned later. Much better layers were grown by MOCVD because it is well suited to grown the pivotal low temperature buffer layers and ternaries, and to some extent RMBE. Now there is a revival of the inorganic VPE for its large growth rates, touted for use as native substrates for MOCVD or MBE device growth [5]. In spite of the rapid development of ID-N technology, many problems remain to be overcome. The main technological issue has been and remains to be the lack of native substrates and resultant lack of high crystalline quality of films.
