The influence of kinetic processes at a negative muon track endpoint in doped nondegenerate silicon on the behavior of muon spin polarization

This work is aimed at creating a theoretical basis for analyzing and interpreting the results of muSR experiments in doped nondegenerate semiconductors at temperatures below 50 K, when the influence of kinetic processes at the endpoint of a muon stopping track on the behavior of its polarization is substantial. The effects related to the formation of free electrons and holes in a solid-state plasma at a muon track endpoint are shown to be responsible for the mere possibility of observing negative muon spin precession at the muon frequency in doped nondegenerate semiconductors at low temperatures. The Vangsness-Bloch equations are generalized to the case of parameters varying with time. A theory based on these generalized equations allowed us to interpret more correctly the available experimental results of muSR studies of semiconductors with the use of negative muons. We showed that the muSR method could be used to obtain information about the cross sections of exchange scattering of electrons and holes by impurity centers in the region of energies inaccessible to the other measurement techniques and to estimate the cross section of capture by a solitary charged Coulomb center at virtually all charge carrier concentrations and temperatures. Under the conditions when the Debye radius is larger than the mean distance between charged particles but smaller than the Thomson radius, the capture (recombination) cross section is described by a temperature dependence qualitatively different from that predicted by current theory. (C) 2004 MAIK "Nauka/Interperiodica".