Threshold behavior of (GaAl)As-GaAs lasers at low temperatures

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Abstract
The temperature dependence of the threshold current, differential quantum efficiency, and internal loss have been measured in the temperature range 10–293 °K. The threshold current increases relatively slowly with temperature above 100 °K and is independent of the impurity concentration. Theoretical calculation shows that this behavior is to be expected for a band‐to‐band transition that follows k selection. The threshold behavior at low temperatures (? 80 °K) depends strongly on the type and concentration of the impurity. The relatively fast decrease in threshold below 100 °K shows saturation for an active layer with n‐type impurities or with high‐concentration p‐type impurities. The saturation is attributed to the carrier diffusion length becoming smaller than the active‐layer thickness. The internal differential quantum efficiency is near unity and is independent of temperature. The internal loss, however, decreases with temperature due to reduction in free‐carrier absorption.