CaF2 overlayers to preserve the ideal termination of Sb/GaAs(110)

Abstract

Photoemission spectroscopy has been performed on CaF2 overlayers on as cleaved (‘‘bare’’) GaAs(110) and GaAs(110) terminated with 1 monolayer of Sb. We observe Fermi-level positions of 0.7 and 0.9 eV above the valence-band maximum on n type for the bare and Sb terminated surfaces, respectively. On p type, we observe close to flatbands for both surfaces. These Fermi-level positions are 0.45 eV on n type and 0.8 eV on p type, below previous reports for CaF2 on the bare surface. We obtain positions close to the previous results by exposing the sample to a flux of UV photons. Upward Fermi-level movement is observed on n and p type for both surfaces. Several complimentary experiments will be discussed which indicate that the observed Fermi-level movement is not due to surface charging. We present a possible interpretation of the data which involves a low density of interface states created by the CaF2deposition and the formation of F centers when the sample is exposed to UV radiation. Analysis of core-level line shapes suggests the presence of Ga–F bonding for CaF2 on the bare surface. We present results which indicate that the ideal Sb termination is preserved for CaF2 on Sb terminated GaAs and evidence of CaF2–Sb bonding will be discussed.