Spin relaxation of charged centers in silicon in the presence of photocarriers (Si : Cr+, [Cr+-B-])

Spin relaxation of deep charged centers Cr+ and of donor-acceptor pairs (Cr +-B-)(0) in silicon is studied by nonstationary EPR spectroscopy at liquid- helium temperatures. We observed the effect of an increase in the spin-latt ice relaxation rate under band-to-band sample illumination; the magnitude o f the effect is proportional to the photoelectron concentration. The spin-d ependent carrier trapping is shown to play a dominant role in spin relaxati on under illumination for centers of both types. Coupled rate equations des cribing the interaction of various subsystems with one another and with the bath are solved. A comparison of experimental data with theory yielded the electron trapping cross sections sigma (r)(Cr+) congruent to 4.9 x 10(-12) cm(2) and sigma (r)(Cr+-B-) congruent to 1.6 x 10(-12) cm(2) at T = 4.2 K. The results obtained are discussed in terms of the theory of trapping by a ttractive centers. (C) 2001 MAIK "Nauka/Interperiodica".