Surface kinetics of GaN evaporation and growth by molecular-beam epitaxy

The kinetics of surface processes during the growth of GaN by molecular-bea m epitaxy (MBE) with ammonia as the source of reactive nitrogen is studied theoretically and experimentally. A model of surface processes is developed taking into account specific effects of the blocking of NH3 adsorption sit es by Group III and Group V surface species. Parameters of the model (respe ctive kinetic rate constants) are determined from comparison with experimen tal data. It is shown that the evaporation rate of GaN in ammonia atmospher e is much lower than that in vacuum. Kinetics of GaN growth under gallium-r ich and nitrogen-rich conditions are compared. Under nitrogen-rich conditio ns the GaN surface is predicted to be enriched by NH, surface radicals, in contrast to the case of growth under gallium-rich conditions or of free eva poration in vacuum. It is shown that use of the nitrogen-rich conditions al lows one to increase the growth temperature by similar to 80-90 degrees C c ompared with the case of gallium-rich conditions or plasma-activated MBE. T he increased growth temperature is favorable in improving the optical and e lectrical properties of the material grown. (C) 2000 Elsevier Science B.V. All rights reserved.