Positron probing of point V-group impurity-vacancy complexes in γ-irradiated germanium

It was found that (i) the trapping cross section of positrons by the radiation complexes is over the range of (0.7-4.3)×10−15 cm2, and (ii) the size of V-group-atom situated in nearest environment of the positron plays crucial role in generating elementally specific emission of the annihilation γ-quanta. The positron-sensitive vacancy-V-group-atom impurity complexes, or E centres, are formed under γ-irradiation at room temperature in oxygen-lean n-Ge〈V〉 (V=As, Sb, or Bi); this process is accompanied by removing free electrons and at higher doses of irradiation the n-p-conversion occurs. Deeply converted material of p-type contains acceptor centres whose energy levels depending on V-group-atom size are over the range of Ev+(0.1-0.16) eV. The positron annihilation data are interpreted in terms of successive trapping of vacancies by the E centres to be formed, in particular, before n-p-conversion of γ-irradiated material.