III-V NITRIDES - THERMODYNAMICS AND CRYSTAL-GROWTH AT HIGH N-2 PRESSURE

In this paper, thermodynamical properties of AIN, GaN and InN, melting , thermal stability and solubility in liquid Al, Ga and In at N-2 pres sures up to 20 kbar are considered. It is shown that significant diffe rences in the thermodynamical properties of AlN, GaN and InN are cause d mainly by different bonding energy in the solid phase. These differe nces lead to different results in the crystal growth of AlN, GaN and I nN from the solutions in liquid Al, Ga and In, at high nitrogen pressu re. High quality, 1-mm single crystals of GaN can be grown in a 5-24 h processes. The crystallization of AlN is less efficient due to the re latively low solubility of AlN in liquid Al, in the experimentally acc essible temperature range. Possibility for the growth of InN crystals is strongly limited since this compound loses its stability at T > 600 degrees C, even at 20 kbar N-2 pressure. The mechanisms of nucleation and growth of GaN crystals is discussed on the basis of the experimen tal results. The quality of the 1-mm and 1-cm GaN single crystals is c ompared and discussed in terms of growth stability, which is the neces sary condition for obtaining high quality, large single crystals of Ga N. The physical properties of pressure grown crystals are reviewed bri efly.