Electronic structure of Zn, Cu and Ni impurities in germanium

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We present a density functional modelling study of Zn, Cu and Ni impurities inhydrogen-terminated germanium clusters. Their electronic structure is investigated indetail, especially their Jahn–Teller instabilities and electrical levels. Interstitial andsubstitutional defects were considered and the latter were found to be the most stabledefect form for nearly all Fermi level positions. Relative formation energies are estimatedsemi-empirically with the help of the measured formation energy of the single Ge vacancy.We find that while Zn is a double shallow acceptor, Cu and Ni are deep acceptors withlevels close to the available experimental data. Donor levels were only found for interstitialCu and Zn.