Studies of the VO centre in Ge using first principles cluster calculations

The small or near-zero band gap of germanium found by supercell local density functional treatments causes difficulties in the study of the properties of charged defects in Ge. Here, we use large H-terminated Ge clusters together with a non-linear core corrected (NLCC) Ge pseudopotential to explore the structure, vibrational and electrical properties of the vacancy–oxygen complex (VO). The cluster possesses a gap sufficiently wide to contain defect related energy levels, thus allowing us to model the three charge states of the defect.The local vibrational modes (LVM) calculated for the neutral (VO0VO0), negatively charged (VO-VO-) and double negative (VO=VO=) defect are 602, 684 and 694cm-1, and can be favourably compared with experimental values of 621, 669 and 716cm-1, respectively [Markevich VP, et al. Physica B 2003; 340–2, 844–8]. Using substitutional gold (AusAus) as a marker defect, electric levels of VO are found at E(-/0)=Ev+0.30eV and E(=/-)=Ec-0.29eV, in excellent agreement with the respective experimental enthalpies for hole and electron emission ΔHh(-/0)≃0.32eV and ΔHe(=/-)=0.26eV, respectively. Finally, the migration, dissociation and reorientation energies of the defect are also reported.