Dissociative surface reactions at Schottky and heterojunction interfaces with AlAs and GaAs

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Abstract
We have conducted synchrotron radiation excited photoemission measurements of the initial stages of Au, Ge, and Ga deposition on AlAs(110) and (100) surfaces grown in situ by molecular beam epitaxy (MBE). Au evaporated onto room temperature AlAs produces a larger dissociation of the substrate surface then reported for Au on GaAs. However, the net Au–AlAs interdiffusion is smaller than for GaAs as seen by the more rapid approach of the Au(5d) and (4f) spin‐orbit splittings to the bulk metallic values. Ge depositied onto AlAs(110) produces a dissociative outdiffusion of As at growth temperatures where abrupt, epitaxial Ge–GaAs(110) interfaces are produced. Since the bulk heat of formation of AlAs is over 50% greater than that of GaAs, the bulk compound heat of reaction incorrectly predicts the behavior of both Schottky and heterojunction interfaces. We conclude that it is the surface adatom bonding to the individual substrate constituents which determines the ultimate interface composition and extent. When the AlAs surface dissociates during interface formation, the Al does not substantially diffuse through the growing Au or Ge overlayers, in marked contrast to Ga from GaAs. Therefore, if metal adlayers are evaporated onto surfaces to influence the subsequent formation of Schottky interfaces, their mobility at the nominal interface is controlled by the bonding of the individual atomic species.

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