Calculation of hopping-conduction energy of holes in SiO 2 based on molecular orbital theory

Abstract

We have developed a new molecular-orbital (MO)-theory-based procedure for calculating activation energies for hole-hopping in dielectrics. The hole-hopping is assumed to consist of two steps. First, the hole hops directly from one trap site to another by electronic excitation without changing atomic structure. Then, the atomic structure gradually relaxes as the hole remains at the newly trapped site. We calculated the excitation energy for hopping to both the nearest-neighbor site and second-nearest-neighbor site in SiO 2. This calculation covered two types of trap sites: O atom (2p lone-pair MO) and O-vacancy (Si–Si bonding MO). The calculation showed that (1) the energy for O-to-O-vacancy nearest-neighbor site hopping was 1.55 eV, which was 1.29 eV lower than that for O-to-O hopping; and (2) the energies for O-to-O-vacancy and O-to-O second-nearest-neighbor hopping were higher than those for nearest-neighbor hopping. This technique will be a useful tool for understanding atomistic-scale hole conduction in oxides and is applicable to other dielectrics such as nitrides and oxynitrides.