Regensburg 2010 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 43: Electronic Structure and Atomistic Modeling

HL 43.3: Talk

Wednesday, March 24, 2010, 14:30–14:45, H14

Exploring the unusual diffusion of N adatoms on GaAs(001) using first principles calculations — •Hazem Abu-Farsakh and Jörg Neugebauer — Max-Planck-Institut für Eisenforschung GmbH, Max-Planck-Straße 1, 40237 Düsseldorf, Germany

The large band-gap bowing resulting from the incorporation of N in GaAs has attracted a considerable interest recently for various applications including e.g. infrared laser diodes. However, epitaxial growth of dilute nitride alloys is hampered by several challenges. A key issue is the low solubility of N in this material system, which requires growth conditions far away from equilibrium. To optimize such conditions it is crucial to employ accurate simulation techniques. Key input quantities include diffusion paths and barriers on the growing surface. To determine these parameters we first employed ab-initio calculations to map the potential energy surface (PES) of N on GaAs(001) surface. Our results reveal that the energy landscape is highly complex and multivalued in nature. A detailed analysis showed that this is a consequence of the high reactivity of the N adatoms causing large surface relaxations. A consequence of this finding is that the conventional PES mapping approach dramatically fails. We therefore propose an alternative approach that allows us to identify the diffusion coefficients and the activation barriers over the entire relevant temperature range. Our results show a completely unexpected interplay of localization within the reconstructed surface unit cell that prevents equilibration and high mobility inside it guaranteeing the incorporation on the desired substitutional sites.