Abstract
The rate of recombination due to spontaneous emission of light at lasing threshold is calculated for a direct band gap semiconductor. The recombination rate for doped semiconductor, where the donor state is assumed to be discrete, is numerically estimated in the temperature range from 50°K to 400°K and compared with the undoped case. It is shown that the threshold of excitation rate for lasing action is decreased by introducing donors (or acceptors) to a host semiconductor.