Band structures and native defects of ammonia borane

Abstract

Band structures and native defects in molecular solid ammonia borane (AB) are investigated by using first-principles calculations based on the density-functional theory (DFT). The native defects include ${\text{NH}}_{3}$ and ${\text{BH}}_{3}$ antisites, interstitials, and vacancies in the various charge states. Despite that the AB crystal is an insulator with a DFT band gap larger than 6 eV, some of the charge-neutral native defects can be abundant, especially at the ${\text{NH}}_{3}$-rich growth conditions, due to their exceptionally low formation energies. This is in sharp contrast to defects in semiconductors for which the formation energies of charge-neutral defects are usually high and correspondingly the concentrations of those defects are low.