IR-spectroscopy of impurity complexes in germanium

Abstract

A large number of impurity complexes which create shallow levels, have been discovered in pure and doped germanium single crystals. The structure and the composition of several of these complexes have been determined using far-infrared spectroscopy and information about crystal growth related residual impurities. In general, the complexes consist of a heavy substitutional impurity binding one or more light. interstitial impurities such as hydrogen or lithium. The coupling between the tunneling motion of the interstitial component and the electronic structure of the complexes can create complicated ground state manifolds which contain stress insensitive components. Spectroscopy further shows that multivariate centers, such as double or triple acceptors, become hydrogenic complexes upon binding one or two hydrogen atoms, respectively. Neutralization of shallow acceptors in silicon, which has recently attracted attention, appears to be the same phenomenon as the valency reduction of multiple acceptors in germanium.