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

Abstract

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 E c, respectively. The acceptor transition involves a structural change between AB and BC forms. Considering the 0.1 eV difference between these configurations, the AB 0→AB –+h + vertical transition is placed below E v+0.1 eV, which may explain the failure of DLTS in detecting such a shallow level.