A rate equation model for the growth of GaN on GaN(000(1)over-bar) by molecular beam epitaxy

GaN(<000(1)over bar>) films were grown by molecular beam epitaxy using ammo nia and elemental Ga. The surface reactivity and growth kinetics of GaN(<00 0(1)over bar>) were investigated as a function of growth parameters using d esorption mass spectroscopy. Growth proceeds either by island nucleation or by step flow, depending on the steady state surface coverage of Ga. Three Ga adsorption states were found on the surface, one chemisorption and two w eak states. One of the weak states corresponds to Ga adsorbed on a gallided surface, while the other corresponded to an intrinsic physisorption state on a hydrogen-passivated, nitrided surface. An abrupt growth mode transitio n between excess Ga and excess nitrogen was found as a function of growth p arameters. The transition was modeled by rate equations based on growth at step edges and the three types of adsorption states. (C) 2000 American Inst itute of Physics. [S0021-8979(00)03802-0].