First-principles study of sulfur passivation of GaP(001) surfaces at one-monolayer coverage

Using first-principles total energy method, we have studied the structural and electronic properties of Ga- and P-terminated GaP(001)(1×2) surfaces adsorbed with one monolayer of sulfur. It was found that the sulfur atoms prefer to occupy bridge sites and the periodicity becomes (1×1) on both Ga- and P-terminated surfaces. The S–Ga bond was confirmed to be stronger than the S–P bond. The electronic analysis showed that the surface state within the energy gap on the Ga-terminated GaP surface was noticeably reduced by the sulfur adsorption, while such reduction does not occur on the P-terminated surface due to the S–P antibonding state. The nearly filled S dangling bonds on the Ga-terminated surface make this surface resistant to contamination.