Divacancy defects in germanium studied using deep-level transient spectroscopy

The divacancy defect in germanium is surrounded with substantial controversy. In this work past speculations about the presence and nature of this defect are critically reviewed. A detailed deep-level transient spectroscopy (DLTS) investigation of radiation damage introduced in p-type germanium diodes by high-energy electrons, protons, and alpha particles has been carried out. As a result it is concluded that the divacancy defect introduces only a single energy level at E-v + 0.19 eV in the band gap as seen by DLTS. The annealing temperature of the corresponding DLTS peak is found to be 415 K. It is further argued that the observed transition involves two holes due to the presence of a single acceptor and a double acceptor with an Anderson negative-U ordering. We observe that the divacancy is not present after low-temperature electron irradiation. This is ascribed to vacancy capture, transforming the divacancy into a trivacancy.