Synchrotron radiation studies of electronic structure and surface chemistry of GaAs, GaSb, and InP

Abstract

The oxidation properties of GaAs(110), GaSb(110), and InP(110) have been studied with the photoemission technique using synchrotron radiation. One part of the work consisted of an investigation of the chemical shifts in the core levels upon adsorption of oxygen in submonolayer quantities. For GaAs and InP, oxygen removed electrons preferentially from the surface column V elements (As and P), leaving the column III elements (Ga and In) unaffected; whereas, for GaSb, both constitutents were involved in the oxidation suggesting a breaking of bonds between the surface atoms and the rest of the crystal. The second part of the study consisted of a careful investigation of the Fermi level (Ef) pinning in the GaAs(110) surface. Three different samples and many cleaves were studied. For one sample, Ef was always at the bulk position. On the other two crystals, both pinned and unpinned cases were found on various cleaves. The unpinned samples had sharp electron distribution curves (EDC’s), while the pinned samples had smeared EDC’s which became sharp for exposures as small as 10 L (1 L=10−6 Torr sec) O2. This, coupled with partial yield spectra showing little change up to 105 L O2, implied that the pinnings on the cleaved surface were due to extrinsic states and that the empty surface states were located in the conduction band. All samples showed pinning at midgap after an exposure of 104 L O2(<1% monolayer). Large changes in the valence band upon oxidation also indicate the possibility of surface resonances in the region 1 to 2 eV below the valence band maximum.