The Carrier-Recombination Behavior and Annealing Properties of Radiation-Induced Recombination Centers in Germanium

An investigation has been made of the carrier-recombination behavior and annealing properties of radiation-induced recombination centers in germanium. In order to analyze the recombination behavior, it has been necessary to treat the problem of recombination in the presence of trapping. A model which explains the experimental results in both n- and p-type material for various sorts of irradiation is presented. On the basis of this model, recombination occurs at an energy level 0.36 ev above the valence band in gamma-irradiated, n- type germanium. The position of this level is shifted slightly downward for neutron-irradiated material. An energy level apparently present in unirradiated material acts as a trapping center in p-type germanium. It is difficult to obtain a value for the electron-capture cross sections, but under certain assumptions a value for the electron-capture cross section in n- type material is obtained: 7 x 10^-19 cm². The annealing behavior of antimony-doped germanium is grossly different from that of arsenic-doped material. Although the annealing behavior is rather complicated, the results are consistent with the following model. Irradiation produces three major types of defects: interstitials, vacancies, and vacancy-interstitial pairs. The vacancy-interstitial pair evidently is responsible for a trapping level located 0.25 ev above the valence band. Both the interstitial and vacancy act as acceptors. The recombination level at 0.36 ev belongs to the vacancy. The interstitial becomes mobile above room temperature and either anneals or forms a complex with an impurity atom. It is thought that the trapping level located 0.17 ev above the valence band might be due to an arsenic-interstitial pair. The activation energy of motion for the interstitial is about 0.8 ev. At a somewhat higher temperature the vacancy becomes mobile with an activation energy of motion of approximately 1.1 ev. In antimony-doped material the vacancy disappears by association with an antimony atom. This process does not occur in arsenic-doped material, and higher temperatures are required to produce annealing.