1ST-PRINCIPLES STUDY OF FULLY RELAXED VACANCIES IN GAAS

The structural and electronic properties of vacancies in GaAs have been studied using ab initio molecular dynamics. The atomic structures of vacancies in different charge states have been optimized by using a simulated-annealing procedure. The neighbor-atom relaxations are modest for neutral, singly negative, and doubly negative Ga vacancies as well as for the neutral As vacancy. In the case of singly and doubly negative As vacancies, very strong inward relaxations are found. These inward relaxations almost recover the fourfold coordination of the neighboring Ga atoms of the vacancy. The analysis of recent positron-annihilation experimental data is discussed in the light of these results.