Angle-resolved photoemission studies of surface states on (110) GaAs

Abstract

Synchrotron radiation was used to study the angle-resolved uv photoemission spectra (UPS) of the (110) surface of GaAs. The wide photon energy continuum (hν<30 eV) coupled with 40 angular resolution permitted the identification of two occupied surface states, centered at ∠−1 and ∠−7 eV measured from the valence band (VB) maximum. These states have not previously been observed in photoemission experiments due to their degeneracy with the bulk VB emission. The relatively new technique of angle-resolved UPS enables one to obtain dispersion information about occupied states and thus lends itself to discriminating between surface and bulk transitions. Since the parallel component of the electron’s momentum is conserved upon leaving the sample, portions of the occupied surface band structure could be identified and mapped out. These were found to be in qualitative agreement with the dispersions predicted by Joannopoulos and Cohen. Sensitivity of the emission to surface contamination served as a test of their surface character.