Electronic surface states on cleaved GaP(110): Initial steps of the oxygen chemisorption

Abstract

Using contact potential difference measurements and photoemission yield spectroscopy, the surface state distribution in the band gap has been obtained for n- and p-type GaP(110) surfaces. All cleavages of n-type samples exhibit a band bending of approximately 0.5 eV. Correlatively, a small density of occupied surface states is found in the vicinity of the Fermi level. From comparison with calculations involving different kinds of surface reconstructions, it is thought to correspond to the tail of an intrinsic surface state band, mainly empty. Another surface state band, the shape and magnitude of which depend on the cleavage, is detected near the valence band maximum. Upon low oxygen exposure, while the band bending increases for n-type samples, the surface state distribution in the gap is modified, new states appearing close to the valence band top. Possible explanations involving surface relaxation or missing surface atoms are suggested.