Photoemission studies of heterojunction interface formation: Ge–GaAs(110) and Ge–Si(111)

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Abstract
A comparison between the formation mechanisms of Ge–GaAs(110) and Ge–Si(111) interfaces is presented. The localized valence band states and core-level states were detected by photoemission spectroscopy with synchrotron radiation. Evidence was found that both kinds of interfaces are sharp and that Ge forms smooth overlayers at room temperature. The shifts in energy of the localized electronic states saturates at a much earlier stage of the interface formation for Ge–GaAs than for Ge–Si. The measured band discontinuities sharply disagree with the predictions of ’’linear’’ interface models. More sophisticated interface models give band discontinuities in excellent agreement with our experimental results for Ge–GaAs—while no satisfactory theoretical explanation is currently available for our Ge–Si results.