Variation of n-GaAs (100) interface Fermi level by Ge and Si overlayers

Abstract

The interface Fermi level (EiF) for interfaces that were formed by depositing thin (∼10 Å) layers of Ge and Si onto heated GaAs (100) substrates was studied by x-ray photoelectron spectroscopy. The value of EiF for Ge overlayers (relative to the GaAs valence band maximum) could be varied from ∼0.5 eV to ∼1.2 eV by depositing the Ge in vacuum or by depositing it in an As4 or P2 background pressure (∼10−7 Torr). These EiF values roughly correspond to the band edges of Ge at the Ge/GaAs heterojunction interface, which suggests that the dopant type in the Ge overlayer and band alignment play a significant role in determining EiF. A thin Si overlayer with incorporated As also exhibited an EiF of ∼1.2 eV. The results suggest that heterojunction band alignment characteristics for Ge/GaAs and Si/GaAs based electrical contacts are important in determining the range over which EiF can be varied. The large EiF variation could have an application in the design of nonalloyed GaAs ohmic contacts.