Ga kinetics in plasma-assisted molecular-beam epitaxy of GaN"112 ¯ 2…: 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﴾112¯2﴿ and GaN{101¯3}. The dominant phase is GaN﴾112¯2﴿ with GaN║ sapphire and GaN║ sapphire in-plane epitaxial relationships. Deposition of GaN on top of an AlN﴾112¯2﴿ buffer layer and growth under slightly Ga-rich conditions reduce GaN{101¯3} precipitates below the detection limits. Studies of Ga adsorption demonstrate that it is possible to stabilize up to one Ga monolayer on the GaN﴾112¯2﴿ surface. The presence of this monolayer of Ga excess on the growth front reduces the ﴾112¯2﴿ surface energy and hence minimizes the surface roughness. Photoluminescence from two-dimensional GaN﴾112¯2﴿ layers is dominated by a near-band-edge emission, which is assigned to excitons bound to stacking faults, present with a density around 3x105 cm−1.

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