CAF2 OVERLAYERS TO PRESERVE THE IDEAL TERMINATION OF SB GAAS(110)/

Photoemission spectroscopy has been performed on CaF2 overlayers on as cleaved (''bare'') GaAs(110) and GaAs(110) terminated with 1 monolaye r 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 surf aces. 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 f lux of UV photons. Upward Fermi-level movement is observed on n and p type for both surfaces. Several complimentary experiments will be disc ussed which indicate that die 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 CaF2 deposition and the formation of F centers when the sample is exposed t o UV radiation. Analysis of core-level line shapes suggests the presen ce of Ga-F bonding for CaF2 on the bare surface. We present results wh ich indicate that the ideal Sb termination is preserved for CaF2 on Sb terminated GaAs and evidence of CaF2-Sb bonding will be discussed.