Electronic structure of hydrogen-vacancy complexes in crystalline silicon: A theoretical study.

Abstract

We report self-consistent calculations for the electronic structure of four complex defects, namely the monohydrogen-vacancy (VH), dihydrogen-vacancy (V${\mathrm{H}}_{2}$), trihydrogen-vacancy (V${\mathrm{H}}_{3}$), and quadrihydrogen-vacancy (V${\mathrm{H}}_{4}$) complexes, in crystalline silicon. The calculations are based on a semiempirical tight-binding theory. Each of the defects is described by a large repeated supercell. To overcome the difficulties in the treatment of large Hamiltonian matrices, we use the recursion method for computing the local densities of states and the localization of the defect states. We have also calculated numerically the wave functions of the fundamental gap states, which are, in turn, used to derive the hyperfine interaction parameters arising from the paramagnetic spin of the wave functions of the gap states for the complex defects. We have found that, in the V${\mathrm{H}}_{4}$ defect, the electrical activity is passivated by four hydrogen atoms, in agreement with early theoretical studies. For the defects VH, V${\mathrm{H}}_{2}$, and V${\mathrm{H}}_{3}$, we have found that the electrical activity is only partially passivated. We show that the nonhydrogenated silicon dangling orbitals are responsible for the remaining electrical activity. We also demonstrate that the Si-H bonding and antibonding states interact very weakly with the silicon dangling-bond states. Models accounting for the electronic structure of the four defects are presented. The effects of the symmetry-conserved distortions and the Jahn-Teller distortions on the electronic structure of the defects are examined. The calculations have been done in detail for the experimentally well-studied V${\mathrm{H}}_{2}$ defect. The results of these calculations agree well with recent experimental studies on this defect.