Control of electronic properties of high-k gate oxides with doping from first-principles calculation

We investigate the microscopic mechanisms not only of crystallization inhibition but also of band gap narrowing (BGN), focusing on an experimental range of nitrogen (N) concentrations, in order to estimate the real potentiality of N doping, and to select much more efficient dopants than N. Oxygen vacancy, Vo, appearance mechanism with N doping is the exothermic reaction. The binding energy of NsVoNs is too small to fix the Vo near the doped Ns site. Because Vo can move easily, total energy is lowered by crystallization around Vo. A large amount of N is needed to be in amorphous phase. However, a large amount of N induces the conduction band (CB) lowering owing to Vo-Vo interaction. The most important point is that Vo should be strongly fixed around the dopants to be in amorphous phase without the CB lowering. Binding energy of BaVo is estimated to be more than six times as large as that of NsVoNs. Moreover, Ba-doping exhibts no BGN. We propose that Ba should be one of the most efficient dopants.