The kinetics of electron transitions for donors with excited states

A new theory of the kinetics of non-equilibrium phenomena involving shallow donors with excited levels is presented, applicable to experiments on photoconductivity, impact ionization, current-controlled negative resistance, and the like. For the steady-state case the solution obtained is rigorous. For the transient case a rigorous solution would not in general be feasible, but it is shown that under certain conditions of sample purity it reduces to a trivial modification of the steady-state solution. Numerical results are given for the requisite region of sample purity.