Preparation of clean GaAs(100) studied by synchrotron radiation photoemission

Abstract

Chemical cleaning of the GaAs(100) surface has been studied with high-resolution photoemission spectroscopy using synchrotron radiation (in the range of 30–1300 eV) at the Stanford Synchrotron Radiation Laboratory. The high surface sensitivity of the technique has allowed us to identify the chemical state of the surface species after both the chemical cleaning and final vacuum processing steps. In order to eliminate contamination from the surroundings, all chemical cleaning steps were performed in an Ar purged glovebox attached to the load lock allowing samples to be transferred into the system without being exposed to air. Samples were etched in H2SO4:H2O2:H2O solution and then heat cleaned in vacuum at 500 °C. After chemical etching in the solution, elemental As (∼2 ML), arsenic oxides (<0.2 ML), gallium oxides (<0.2 ML), and C (0.5∼1 ML) are found on the surface. Subsequent annealing at <500 °C in ultrahigh vacuum produces a stoichiometric, oxide-free surface as determined by valence-band and core-level photoemission. In addition, C has been reduced to less than 0.1 ML. We believe that the C can be removed by heating because the elemental As from the earlier cleaning step tends to protect the GaAs surface. The chemical reactions and species at different cleaning stages are discussed.