The deterioration of gain in electron-beam-pumped semiconductor lasers with increase in the diameter of the pumped region has been attributed to a reduction in the degree of inversion caused by amplified spontaneous emission. Theories of amplified spontaneous emission in such surface-emitting lasers are advanced in which spatial and spectral inhomogeneities of gain are taken into account. Experiments to determine the dependence of laser threshold and differential efficiency on the diameter of an excited circular region demonstrate good agreement with the threshold predictions of the linear theory; however, the lack of agreement in differential efficiency suggest that a nonlinear phenomenological theory be considered. Data for such calculations are provided from experiments on saturation of spontaneous emission. The resultant nonlinear theory is shown to account well for the observed dependence of differential efficiency on the diameter of the excited region.
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