Ga kinetics in plasma-assisted molecular-beam epitaxy of GaN(11(2)over-bar2): Effect on the structural and optical properties

GaN directly deposited on m-sapphire by plasma-assisted molecular-beam epitaxy settles into two main crystalline orientation domains: GaN(11 (2) over bar2) and GaN{10 (1) over bar3}. The dominant phase is GaN(11 (2) over bar2) with < 11 (2) over bar(3) over bar >(GaN)parallel to < 0001 >(sapphire) and < 1 (1) over bar 00 >(GaN)parallel to < 11 (2) over bar0 >(sapphire) in-plane epitaxial relationships. Deposition of GaN on top of an AlN(11 (2) over bar2) buffer layer and growth under slightly Ga-rich conditions reduce GaN{10 (1) over bar3} precipitates below the detection limits. Studies of Ga adsorption demonstrate that it is possible to stabilize up to one Ga monolayer on the GaN(11 (2) over bar2) surface. The presence of this monolayer of Ga excess on the growth front reduces the (11 (2) over bar2) surface energy and hence minimizes the surface roughness. Photoluminescence from two-dimensional GaN(11 (2) over bar2) layers is dominated by a near-band-edge emission, which is assigned to excitons bound to stacking faults, present with a density around 3x10(5) cm(-1). (C) 2008 American Institute of Physics.