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

Abstract

For the first time the positron probing of the vacancy—V-group-atom impurity complexes, which were created by γ-irradiating 60Co ( T irr.≈280 K) in the oxygen-lean n-Ge〈V〉 (V=As, Sb, or Bi), has been conducted systematically both before and after n-p-conversion of material. The one-dimensional angular correlation of the annihilation radiation (ACAR) has been registered for crystallographic directions [1 1 1], [1 1 0], and [1 0 0]. The concentration of defects in the same samples was determined from the temperature dependencies of the carrier density and mobility obtained over the range of 4.2–300 K. 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 cm 2, 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 E v+(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.