Papers by Keyword: Core Electrons

Abstract: Angular correlation of annihilation radiation technique (ACAR) has been used for studying a microstructure of the vacancy-group-V-impurity complexes (DV) formed by irradiation with 60Co γ – rays at Tirr. ≈ 280K in oxygen-lean n-Ge doped with group-V-impurity atoms As, Sb, and Bi. The probability of annihilation of positrons with the core electrons of DV complexes to be reconstructed from ACAR spectra has been analyzed on the basis of Chapman-Kolmogorov formalism; the Coulomb repulsion is proved to regulate the penetration of a positron into Ge4+ and D5+ ion cores. In passing from AsV to SbV and BiV complexes the ion cores D5+ are found to contribute more effectively to the probability of the positron annihilation in the core region. These data correlate well with the augmentation of the entropy of ionization (4S ~ 2,9 ÷ 4,2K) observed by means of capacitance transient techniques with the use of Au-Ge Schottky barriers in the same row of a similar vacancy-impurity complexes. The results obtained by ACAR spectroscopy suggest the full-vacancy configuration of DV pair with relaxation of atoms inward towards the vacancy.

Abstract: A probing of the atomic environment of positron in Cz-Si single crystal heat-treated at T=600C and T=450C has been performed by one-dimensional angular correlation of annihilation radiation (ACAR). It has been established that positrons get trapped by the oxygen-related complexes. The penetration of positrons into the core region of surrounding atoms results in emission of the elementally specific high-momentum annihilation radiation. The processes of expelling of positron from ion cores and its penetration into the core region are regulated by the potential barrier (to be considered as the Coulomb’s one as a first approximation). The characteristic electron-positron ion radius and the probabilities of correlated events of the highmomentum annihilation are due to the chemical nature of the ion cores of atoms involved in the composition of the oxygen-related complexes. The interpretation of the results is based on the notion of the positron localization in the field of negative effective charge resulted from comparatively high electron affinity of the oxygen impurity atom. The presence of a free volume (perhaps, a vacancy) as well as the carbon atom in the microstructure of the oxygen-related positron-sensitive thermal defects is briefly discussed.