Theory of Hydrogen in Diluted Nitrides

At variance with the mechanisms responsible for the passivation of typical shallow dopants in GaAs, where H bonding with the impurity or to its neighbors permits a recovery of the "natural" chemical valence of the impurity itself, in the case of the N isoelectronic impurity in GaAs, H induces no changes in the N chemical valence. It breaks, instead, two Ga-N bonds to form complexes sharing a common, quite stable NH2 core characterized by a local C2v-like symmetry, thus strongly perturbing the interactions of N with its four Ga neighbors. A theoretical picture is presented here, where the N effects on the GaAs electronic properties, as well as their passivation upon hydrogenation, are closely related to the local N-Ga interactions and to the perturbations induced by H bonding on the N environment. The formation of multi-H complexes with N, predicted by theory, is also discussed togegher with the support given to their existence by recent experimental findings.