Point Defects in γ-Irradiated Germanium: High- and Low- Momentum Positron Annihilation Study Before and After n-p-Conversion

Abstract

The electron momentum distribution and microstructure of centers incorporating a vacancy (vacancies) and a group-V-impurity atom (P, As, Sb, or Bi) in oxygen-lean n-Ge crystals have been investigated by means of the angular correlation of the annihilation radiation (ACAR). The vacancy-group-V-impurity atom complexes have been induced by irradiation with 60Co γ – rays at Tirr. ≈ 280K. A split between the intensities of the high-momentum emission of the annihilation radiation measured before and after n-p-conversion has been revealed for the complexes containing smaller ion cores (P, As) and the larger ones (Sb, Bi), respectively. After n-p-conversion the electron density decreases slightly (but markedly) around the positron localized at the vacancy complexes incorporating P, Sb, and Bi impurity atom. This decrease is accompanied by a lessening of intensity of the high-momentum emission of the annihilation radiation thus bringing in a direct evidence of a multi-vacancy structure of the vacancy-group-V-impurity atom complexes after n-p-conversion; the electron density was found to be affected by the localized deep acceptor states related to these centers. The relaxation inward open volume is a common feature which is pronounced for As-containing complexes. Subvalent band states are suggested to contribute the high-momentum annihilation most markedly. The electron momentum density around the positron is due to rather by the elemental specificity of the surrounding atoms than by changes of the electron-positron many-body interaction in the vacancy-group-V-impurity atom complexes.