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 pressures up to 20 kbar are considered. It is shown that significant differences in the thermodynamical properties of AlN, GaN and InN are caused mainly by different bonding energy in the solid phase. These differences lead to different results in the crystal growth of AlN, GaN and InN from the solutions in liquid Al, Ga and In, at high nitrogen pressure. 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 relatively low solubility of AlN in liquid Al, in the experimentally accessible 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 experimental results. The quality of the 1-mm and 1-cm GaN single crystals is compared and discussed in terms of growth stability, which is the necessary condition for obtaining high quality, large single crystals of GaN. The physical properties of pressure grown crystals are reviewed briefly.