Effect of an Al interlayer on the GaAs/Ge(100) heterojunction formation

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Abstract
The chemistry, structure, and growth kinetics of epitaxial GaAs/Ge heterojunctions are controllably modified using an Al interlayer of one to two monolayers in thickness. Photoemission spectroscopy is used to investigate the interface formation with and without the Al interlayer. Although the valence-band and core-level spectra indicate dramatic changes of the chemistry and structure caused by the Al (deposited on the substrates both at room temperature and at 340 °C) at the interface, the band-structure lineup is not affected. The Fermi level in the gaps is influenced by both the presence of the Al interlayer and the deposition temperature. The Fermi level moves toward the valence band by 0.15 and 0.3 eV (relative to the GaAs c(4×4)/Ge degenerate n-type interface) for room-temperature and 340 °C deposition, respectively. The Fermi-level position is simply related to the amount of As diffusion into the Ge layer and its role as an n-type dopant. The results support the conclusion that the band offset is primarily an intrinsic (bulk) property which is insensitive to interfacial charge distribution or chemistry to within ±0.05 eV.