Thermal properties of semiconductor lasers, and the interpretation of thermal-resistance measurements

Conventional models of junction heating in semiconductor lasers have been considered, and are found to be inconsistent with the experimental observations on stripe-geometry double-heterojunction lasers. In particular, the onset of the thermal runaway of c.w. threshold current, induced either by increasing the heat-sink temperature or by degradation processes, is found to occur at a current much less than predicted theoretically. Part of the reason for these inconsistencies is that at high temperatures there is a departure from the commonly assumed exponential dependence of pulsed threshold on junction temperature. However, it is the observation that the temperature rise of the active region is not directly proportional to the input power which explains why the experimental results are so different from the theoretical predictions. The results are discussed with reference to a model of multiple heat sources, with sources assuming different relative importance as the input power increases.