GROWTH-KINETICS OF GAN GROWN BY GAS-SOURCE MOLECULAR-BEAM EPITAXY

We report on the incorporation kinetics of gallium during gas-source m olecular beam epitaxy (GSMBE) of GaN using elemental Ga and NH3 gas as source materials. Desorption mass spectrometry (DMS) is used to perfo rm in situ quantitative measurements of GaN formation, Ga desorption a nd Ga surface accumulation during growth. The fate of formation of GaN is reported as a function of incident Ga flux (0.1-0.75 ML/s) and inc ident NH3 flux (1-300 x 10(-7) Torr beam-equivalent pressure) at a con stant growth temperature of 725 degrees C. Three distinct growth regim es are observed: (1) GaN is formed where all of the incident Ga flux i s consumed, (2) part of the incident Ga is consumed to form GaN while the excess is desorbed from the surface, and (3) GaN formation coexist s with desorption and surface accumulation of Ga. It is generally obse rved that the Ga surface accumulation is inhibited by increasing the r ate of incidence of NH3 and/or by decreasing the rate of incidence of Ga at this temperature. In addition, the order of the reaction between Ga and NH3 is determined to be unity, supporting the validity of the Ga + NH3 --> GaN + 3/2 H-2 reaction.