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HL: Fachverband Halbleiterphysik

HL 33: Quantum wires: preparation and characterization

HL 33.2: Vortrag

Mittwoch, 25. März 2009, 14:15–14:30, BEY 81

Nucleation of Au-induced GaAs Nanowires on Si(111) and GaAs(111)B — •Steffen Breuer, Maria Wagler, Lutz Geelhaar, Achim Trampert, and Henning Riechert — Paul-Drude-Institut für Festkörperelektronik, Hausvogteiplatz 5-7, 10117 Berlin

Vertical nanowires (NWs) offer a novel path towards monolithic integration of III-V semiconductors such as GaAs on Si. We studied nucleation and growth of GaAs NWs by the Au-induced vapor-liquid-solid (VLS) mechanism in a molecular beam epitaxy (MBE) chamber on Si(111) and compared it to the homoepitaxial case on GaAs(111)B. NWs grown for 30 min on each substrate are straight and have very similar shapes, lengths and densities, as found by scanning electron microscopy (SEM). We conclude from reflection high-energy electron diffraction (RHEED) patterns that on both substrates the NWs have Wurtzite (WZ) crystal structure and are epitaxially aligned to the respective substrate. A series of experiments with growth times between 5 s and 300 s was performed on each substrate. At this early stage, there are significantly more NWs on GaAs(111)B than on Si(111). Apparently, on Si(111) NW formation is delayed. Instead, the early surface is predominantly covered by three-dimensional GaAs islands that have Zincblende (ZB) crystal structure and a high density of twinning defects, as found by RHEED. We conclude that on Si(111) most Au droplets are inactive initially until the whole surface is covered by coalesced GaAs islands. We speculatively explain this by a model that assumes different interface energies for liquid Au on the two types of substrate.