Regensburg 2002 – wissenschaftliches Programm

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HL: Halbleiterphysik

HL 14: III-V Halbleiter I

HL 14.5: Vortrag

Dienstag, 12. März 2002, 12:00–12:15, H13

Negative step formation energies on GaN surfaces: Implications on surface roughening — •Liverios Lymperakis and Jörg Neugebauer — Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6 , D-14195 Berlin (Dahlem), Germany

Recent experiments show that steps on GaN surfaces exhibit a rather complex behavior: they have different growth rates and some of them are unstable. In order to get a microscopic understanding of these effects we have studied the formation energies and atomic geometry of steps on (0001) and (0001) wurtzite GaN surfaces, employing density functional theory, a plane wave basis set and pseudopotentials. Based on these results we have derived a phase diagram, which gives the energetically favored step structures as a function of the nitrogen chemical potential (partial pressure). We find that under Ga-rich conditions the Ga-terminated surfaces are thermodynamically stable and step formation is endothermic. For extreme N-rich conditions however, step formation becomes exothermic implying that surfaces become unstable against step formation. Based on these results we discuss recent experiments and explain why surface roughening occurs under more N-rich conditions.