Energy levels of atomic hydrogen in germanium from ab-initio calculations

Donor and acceptor levels of atomic hydrogen centers in germanium are calculated by density functional-pseudopotential modeling, using large hydrogen-terminated Ge clusters. We found that the neutral bond centered (BC) and anti-bonding configurations (AB) are energetically very close, with a slight (0.1 eV) preference for the BC structure, which agrees with recent muonium spin resonance (μSR) data and previous supercell ab-initio calculations. The interstitial H defect shows a negative-U level ordering, possessing donor and acceptor levels at 0.28 eV below the conduction band and at about 0.1-0.2 eV above the valence band, respectively. The calculated donor level accounts well for deep level transient spectroscopy (DLTS) and μSR data, which give a (0/+) transition at 0.11 and 0.23 eV below Ec, respectively. The acceptor transition involves a structural change between AB and BC forms. Considering the 0.1 eV difference between these configurations, the AB0→AB-+h+ vertical transition is placed below Ev+0.1 eV, which may explain the failure of DLTS in detecting such a shallow level.