Electronic properties of sulfur-treated GaAs(001) surfaces

We have studied the atomic geometries of the GaAs(001) As-terminated surfaces covered with sulfur overlayers by performing total-energy calculations within an empirical tight-binding model. A number of possible geometries are examined, and several geometries with low total energy are found to be free of surface states in the midgap. The surface band structures and local density of states for some of these geometries are calculated and the surface states are identified. Our results show that by forming a 2×{}1 reconstruction of sulfur overlayers in several different ways, good electronic properties of the GaAs surfaces can be obtained. This lends theoretical support to recent experimental studies in which the GaAs surface was treated with sulfur-related solutions.