Characterization of molecular beam epitaxy grown GaS film for GaAs surface passivation

Abstract

GaAs surface passivation with molecular beam epitaxy (MBE) grown GaS film employing the single precursor, tertiarybutyl-galliumsulfide-cubane ([(t-Bu)GaS] 4), can be used to improve upon previous devices and processing due to Fermi level pinning, for example, nonalloyed ohmic contact to n-GaAs, etc. This report deals with the characterization of MBE-grown GaS film by a transmission electron microscope (TEM), ellipsometry, laser scattering and secondary ion mass spectroscopy (SIMS). The crystalline structure of GaS film changed from amorphous to polycrystalline by increasing the substrate temperature from 350 to 500°C. From a TEM diffraction pattern, the crystalline structure of polycrystalline GaS is identified to be in the zincblende phase. The lattice constant of GaS film was evaluated to be 5.33 Å (5.7% mismatch to GaAs). The refractive index and surface morphology of GaS film changed at the transition region from amorphous to polycrystalline. The amorphization of the GaS film led to excellent surface morphology, which resulted in the suppression of current leakage in a metal–insulator–semiconductor structure. With the insertion of a very thin GaS, we showed the possibility of nonalloyed ohmic contact to n-GaAs. Furthermore, by SIMS analysis measured on the substrate side, we determined that sulfur diffusion from GaS to GaAs is negligible.