Negative-U properties of the lattice vacancy in silicon

Abstract

We present direct and unambiguous evidence that the donor levels of the silicon lattice vacancy are inverted in negative-U ordering, as originally suggested by Baraff et al. The second donor level, at Ev + 0.13 eV, lies above the first donor level, at Ev + 0.05 eV. First, we demonstrate that the Ev + 0.13 eV level is a donor state by the absence of the Poole-Frenkel effect in DLTS studies. Second, we describe a detailed EPR study of the reactions involving hole transfer via the valence band between the vacancy and the shallow aluminum acceptor. By monitoring the intensity of the V+ and Alos EPR signals, all aspects of the negative-U ordering appear to be confirmed.