Millisecond phosphorescence of free electrons in pure GaAs

A very long decay of transient free-to-bound photoluminescence (PL) in pure GaAs at low temperatures has been experimentally found. It is shown that, in undoped or dilutely doped GaAs, the decay of band-to-acceptor PL after a transient excitation follows an essentially nonexponential dependence appr oximated by a power law with the exponent as low as 0.3, and is observed fo r as long as 2.5 ms. The long decays of free-electron PL point to the domin ation of repeated trappings and subsequent releases of free electrons by so me shallow traps, which are suggested to be the shallow donors. (C) 2001 Am erican Institute of Physics.