Si-Si bond as a deep trap for electrons and holes in silicon nitride

A two-stage model of the capture of electrons and holes in traps in amorphous silicon nitride Si$_3$N$_4$ has been proposed. The electronic structure of a “Si-Si bond” intrinsic defect in Si$_3$N$_4$ has been calculated in the tight-binding approximation without fitting parameters. The properties of the Si-Si bond such as a giant cross section for capture of electrons and holes and a giant lifetime of trapped carriers have been explained. It has been shown that the Si-Si bond in the neutral state gives shallow levels near the bottom of the conduction band and the top of the valence band, which have a large cross section for capture. The capture of an electron or a hole on this bond is accompanied by the shift of shallow levels by $1.4$–$1.5$ eV to the band gap owing to the polaron effect and a change in the localization region of valence electrons of atoms of the Si-Si bond. The calculations have been proposed with a new method for parameterizing the matrix elements of the tightbinding Hamiltonian taking into account a change in the localization region of valence electrons of an isolated atom incorporated into a solid.