THERMODYNAMICS AND HIGH-PRESSURE GROWTH OF (AL, GA, IN)N SINGLE-CRYSTALS

Thermodynamical properties of AlN, GaN and InN are reviewed. It is sho wn that significant differences in melting conditions, thermal stabili ty and solubilities in liquid III group metals lead to different possi bilities of growing crystals from high-temperature solutions at N-2 pr essures up to 20 kbar. It is shown that the best conditions for crysta l growth at available pressure and temperature conditions can be achie ved for GaN. High-quality 6-10 mm GaN single crystals have been grown at high N, pressures in 60-150 hour-long processes. The mechanisms of nucleation and growth of GaN crystals are discussed on the basis of th e experimental results. The crystallization of AIN is less efficient o wing to the relatively low solubility of AlN in liquid Al. The possibi lity for the growth of InN crystals is strongly limited since this com pound loses its stability at T>600 degrees C, even at 2 GPa N-2 pressu re. The crystals of GaN grown at high pressure are the first to be use d for homoepitaxial layer deposition. Both MOCVD and MBE methods have been successfully applied. Structural, electrical and optical properti es of both GaN single crystals and homoepitaxial layers are reviewed. (C) 1997 Elsevier Science S.A.