Berlin 2005 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 22: GaN: Pr
äparation und Charakterisierung I

HL 22.2: Vortrag

Samstag, 5. März 2005, 11:00–11:15, TU P-N201

Formation of steps and vicinal surfaces on GaN (0001) surfaces: Implications on surface morphologies and surface roughening. — •Liverios Lymperakis and Jörg Neugebauer — Fakultät für Naturwissenschaften, Universität Paderborn, Fachbereich 6-Physik, D-33095 Paderborn

The most common and technologically most relevant growth direction of wurtzite GaN is normal to the {0001} basal plane. The morphology of these surfaces is known to be extremely sensitive to the growth conditions: Going from N-rich to more Ga-rich conditions a transformation of the morphology occurs accompanied by smoother surfaces and better film quality. Surface steps may act as nucleation and compensation centers and thus play a crucial role in these transformations. In order to get a microscopic understanding of these effects the energetics and geometry of possible step/vicinal surface configurations on (0001) wurtzite GaN surfaces have been studied employing density functional theory, a plane wave basis set, and pseudopotentials. We find that for growth under N-rich conditions steps/vicinal surfaces may spontaneously form on the surface. However, going to more metal-rich conditions we find the steps to be thermodynamically unstable against the formation of the laterally contracted bilayer structure. Based on our calculations we discuss and explain recent experimental observations on surface roughening and growth anisotropy of GaN surfaces.