Ab initio investigation of point defects in bulk Si and Ge using a cluster method -: art. no. 245206

Atomic and electronic structures of various charge states( 2 +, + 0.- 2 -) of monovacancies V and divacancies V-2 in crystalline Si and Ge are calculated from first principles. The calculations are performed in real space on bulk-terminated spherical and prolate clusters that are passivated by hydrogens at the boundaries. Defect-induced Jahn-Teller distortions. Jahn-Teller and relaxation energies, vacancy wave function characters, and hyperfine parameters are calculated and compared with available experimental data. The magnitudes of Jahn-Teller distortions and energies are found to be smaller in Ge compared to Si for both V and V, Unlike in Si, the pairing type distortions induced by a divacancy in Ge are not large enough to result in a deep level crossing inside the band gap. Furthermore. the relaxed atomic configuration,, of the divacancy in Ge with resonant bond type distortions are found to be slightly lower in energy than those with pairing type distortions. The effect of the lattice constant at which the calculations are performed (experimental versus theoretical) is also examined, and found to be quite important, especially for Ge.