Photoemission study of surface states of the (110) GaAs surface

Abstract

A detailed photoemission study of the cleavage face of GaAs shows that there are no empty surface states in the lower half of the energy gap, but empty surface states extend down to about the middle of the energy gap. The empty surface states cause Fermi-level pinning and band bending on $n$-type GaAs, but the bands are approximately flat for $p$-type GaAs. No evidence for filled surface states is found below the valence-band maximum, indicating that any filled surface states below the valence-band maximum have no strong structure and may be strongly mixed with bulk valence-band states. Several theoretical calculations of the surface states for GaAs (110) have been reported which find an empty surface state in good agreement with the results reported here, but the calculations also find a high density of surface states located approximately 0.5 eV below the valence-band maximum, in poor agreement with our results.