Abstract
Impact ionization of shallow centers in n‐GaAs is utilized to control the branching ratio of the two carrier‐recombination channels via shallow centers and via acceptors. We report the first purely optical measurements for the rate of electron capture into an acceptor. This rate is too small to significantly affect, in general, the lifetimes of free excess majority carriers in GaAs at low temperatures; the carrier lifetime is not determined by nonradiative recombination via centers near the middle of the band gap.