Sulfur passivation of GaAs surfaces: A model for reduced surface recombination without band flattening

Abstract

It has been shown by several workers that the passivation of GaAs surfaces using sulfides results in a large reduction in the surface recombination velocity accompanied by an increase in the band bending on n-type samples. This apparently contradictory pair of results leads to the suggestion that the responsible electronic states are a midgap donor compensated by an acceptor near the valence-band maximum. We explore the consequences of such a model, particularly when the midgap state is assumed to be a double donor. In the double donor case, simple qualitative arguments indicate that the surface recombination velocity can be reduced by a factor much greater than the reduction in surface-state density. The model is consistent with observations made using a variety of experimental techniques. A correlation between the electronic states and surface chemistry is made, and the As and Ga antisite defects are discussed as candidates for the donor and acceptor states.