Role of Chemical Potential in Tuning Equilibrium Crystal Shape and Electronic Properties of Wurtzite GaAs Nanowires

GaAs nanowires (NWs) often exhibit wurtzite crystal structure during the vapor liquid solid (VLS) growth, and their sidewalls are generally composed of {1 (1) over bar 00} and {11 (2) over bar0} facets. Owing to the large surface-to-volume ratio, the sidewall structures of NINs are sensitive to the chemical environment. However, the impact of chemical environment on the sidewall structures and electronic properties of wurtzite GaAs NWs is still not clear. Here we present detailed first-principles calculations to investigate the atomic structure of sidewall facets, equilibrium crystal shape, and electronic properties of wurtzite GaAs NWs under different chemical potential conditions. On the basis of the surface energies of sidewall facets, the equilibrium crystal shape (ECS) of NWs is evaluated using the Wulff construction. The ECS of NWs demonstrates a shape evolution from a dodecagonal prism to a hexagonal prism with increasing As chemical potential, which is in agreement with the experimental observations. Meanwhile, the increasing As chemical potential results in a direct indirect band gap transition in wurtzite GaAs NWs due to the structural change of NW sidewalls. This result can be applied successsfully to explain an existing experimental controversy for the band gap of wurtzite GaAs NWs.