Electronic structure of GaF₃ films grown on GaAs via exposure to XeF₂

GaAs(110) and (100) wafers are reacted with XeF₂ at room temperature and studied with soft-x-ray photoelectron spectroscopy (SXPS), photon-stimulated desorption (PSD) and electron-energy-loss spectroscopy (EELS). The reaction between GaAs and XeF₂ results in the homogeneous growth of a GaF₃ film and an interface region consisting of intermediate products. The band gap of GaF₃ and its band lineup with the GaAs substrate are determined via EELS and SXPS. F⁺ PSD spectra collected after the initial XeF₂ exposures indicate a single desorption onset at ∼28 eV, due to the excitation of a F 2s electron to the GaAs conduction-band minimum. PSD spectra collected after larger exposures contain a number of features due to transitions within the GaF₃ band structure. These features appear when the film thickness exceeds ∼10 Å, indicating that the bulk electronic structure has developed. Annealing the film to ∼250 °C results in the inhomogeneous removal of GaF₃.