Structure of the P vacancy on the InP(110) surface from first principles

We have performed density functional theory (DFT) calculations to study the geometric structure of the phosphorus vacancy on the InP(110) surface. The stable structure of the P vacancy depends critically on its charge state. For a (+1) charged P vacancy, the nonsymmetric configuration with one rebonded dimer is favored, while the symmetric configuration shows a saddle point behavior. For a (-1) charged P vacancy, both the symmetric and nonsymmetric configurations are local minima, where the symmetric configuration has the lowest energy. Using the nudged elastic band method, we have determined the reaction path and energy barrier between two configurations for both (+1) and (-1) charged vacancies. The simulated scanning tunneling microscopy (STM) images of the P vacancy on p-type and n-type InP(110) surfaces are calculated and compared with the available experimental results. We support the point of view that the observed STM image of the P vacancy is an average result of thermal flipping between two possible configurations.