PHOTOEMISSION-STUDY OF THE FORMATION OF SRF2/GAAS(100) AND BAF2/GAAS(1OO) INTERFACES

Thin films of SrF2 and BaF2 grown on clean GaAs(100) surfaces have been studied by high-resolution photoemisison spectroscopy. Similar to the previously studied CaF2/GaAs(100) interface, there is evidence of cation-substrate bonding after annealing at temperatures near 600 degrees C. For BaF2, Ba was found to react with As at the interface with an associated loss of Ga and F. For SrF2, the Sr 3d core-level shift also suggests cation-substrate bonding. The valence-band maxima for GaAs and the respective alkaline-earth fluorides (CaF2, SrF2, BaF2) were measured directly by linear extrapolation of the high-kinetic-energy edge of the respective valence bands. The resulting valence-band offsets were found to follow the same trend for coverages up to 2-4 monolayers.