Photoemission study of the formation of theCaF2/GaAs(100) interface

The formation of the interface between ${\mathrm{CaF}}_2$ and GaAs(100) has been studied by high-resolution photoemission spectroscopy. ${\mathrm{CaF}}_2$ thin films were deposited in ultrahigh vacuum by evaporation on clean GaAs(100), and subsequently annealed in steps up to 590°C. By 550 °C, a monolayer of Ca was found to react with As at the interface with an associated loss of approximately one Ga and one F by evaporation per formula unit of ${\mathrm{CaF}}_2$. The thickness of the interfacial layer terminates at one monolayer for the range of annealing conditions studied. The interfacial valence-band offset was found to be 8.5 eV and the Fermi level approaches the GaAs valence-band edge with increasing ${\mathrm{CaF}}_2$ overlayer thickness.