Vacancy-impurity complexes that were believed to be implicated in the de-activation of As in highly n-doped Si were investigated by using density functional theory. The electronic structures and defect levels of the impurities were determined, and it was found that the As1V complex could trap up to 2 conduction electrons at high n-doping. Both As2V and As3V bound a single extra electron at high Fermi levels, and this made these complexes very efficient in de-activating As. The impurity levels were related to the ones found in the isolated vacancy and, in general, all of the As dopants tended to bind their fifth valence electron much more strongly than in the 4-fold coordination, when placed next to a lattice vacancy. The donor level of As in such configurations was thus shifted deeply into the band gap or even below. In the case of the isolated Si lattice vacancy, the calculations predicted that, at very high n doping, it could adopt a charge state of -4 and thus itself act as an effective electron trap center. It was also observed that AsnV2 clusters (n = 2, 3) containing a divacancy could also play an important role in the de-activation of As at lower annealing temperatures.

Arsenic Deactivation in Si - Electronic Structure and Charge States of Vacancy-Impurity Clusters. D.C.Mueller, E.Alonso, W.Fichtner: Physical Review B, 2003, 68[4], 045208 (8pp)