The mystery of the "invisible" Ga vacancy in GaAs

Irradiation of semiconductors with energetic particles results in displacement damage causing device and material degradation. Characterizing the formation and reactivity of atomic defects is imperative in developing an understanding necessary to mitigate detrimental effects in device performance. Primitive displacement damage in GaAs produces vacancies, divacancies, and interstitials. Interstitials are predicted to be mobile. The immobile As vacancy and divacancy defects are predicted to have defect levels as observed in experiments. However, despite also being predicted to be immobile and have defect levels, the Ga vacancy has yet to be observed in any experiment—raising the question: Where is the Ga vacancy? Using an atomistic-aware device modeling approach to explore the chemical evolution of defects in irradiated GaAs, we discover that a strong Coulomb attraction, stemming from a Fermi level shift, drives fast As interstitials to preferentially annihilate Ga vacancies. This dynamical process causes the Ga vacancy defect population to plummet below detectable limit—to disappear. This novel approach solves the mystery of the “invisible” Ga vacancy and reveals the importance of a multiscale approach to probe this experimentally inaccessible short-time regime.