Effect of band tails on stimulated emission of light in semiconductors

The dependence of the stimulated emission of radiation in semiconductors on temperature and on impurity concentration has been calculated using a Kane model with a Gaussian band tail for the density of states, and an optical model with a constant matrix element and no selection rule for the radiative transitions. The screening length and the characteristic energies for the widths of the conduction- and valence-band tails are calculated by a self-consistent procedure, and the calculation has no adjustable parameters. Numerical results are obtained using parameters appropriate for GaAs injection lasers. The presence of band tails leads to a more nearly linear dependence of gain on excitation level, in better agreement with experiment, than did the calculation without band tails by Lasher and Stern. Increasing impurity concentration leads to a weaker temperature dependence of the excitation rate required to reach a given gain. © 1966 The American Physical Society.