Temperature effects for Ti/GaAs(110) interface formation involving cluster and atom deposition

Abstract

Ti/GaAs(110) interfaces formed at 60 and 300 K by atom-by-atom deposition and by the deposition of preformed metallic clusters exhibit very different Schottky-barrier behavior and morphologies. For atom deposition, temperature-dependent Fermi-level pinning is similar to that observed for nonreactive metals, despite the fact that the deposition process leads to the disruption of ∼3 monolayers of GaAs at all temperatures. Although disruption is apparent even at 0.02 Å, atom deposition at 60 K on n-type GaAs shows almost no Fermi-level movement until ∼2 Å when $E_F$ moves rapidly toward midgap. Our results show that the adatoms do not act as nonreactive donors at low temperature, that thermal changes do not quench surface chemistry, and that surface reaction alone does not lead to midgap pinning. In contrast, for interfaces formed by preformed Ti cluster deposition, unique pinning positions are observed far from the point expected for known defects or metal-induced gap states. The instability of the Ti(cluster)/GaAs system is demonstrated by warming to 300 K. We postulate that kinetically restricted reactions occur beneath the metallic clusters and the midgap pinning requires disruption in the presence of a metallic overlayer.