Acceptor-donor pairs in germanium

The formation of acceptor-donor pairs in germanium was studied by perturbed angular correlation spectroscopy. At the single acceptor In the donors P and As were trapped, resulting in In-P and In-As pairs as well as in In-P2 complexes. At the double acceptor Cd three P and two As correlated configurations were formed, i.e. Cd-P and Cd-As pairs, Cd-P2, Cd-As2 and Cd-P3 complexes. In Ge:Sb and Ge:Se the pairing of Cd acceptors with Sb or Se donors was detected. As predicted by calculations of the Coulomb binding energy the stability of the complexes decreases with increasing number of involved donor atoms, and a configuration formed at the double acceptor Cd reveals a higher stability than the analogous one at the single acceptor In. The weak temperature dependence of the corresponding field gradients indicates either electrical inactivity of Cd-donor complexes or the generation of shallow levels. (orig.)