Temperature characteristics of bipolar cascade lasers

The temperature characteristics of bipolar cascade lasers operating up to 80 °C with room temperature, continuous-wave differential slope efficiencies of 93%, are reported. The continuous-wave characteristic lasing threshold temperature, T0, of the device is found to be 103 K for heatsink temperatures below 40 °C, dropping to 56 K for heatsink temperatures in the range 50–80 °C. Two separate regions are found to exist for the characteristic temperature of the differential slope efficiency, T1. The temperature of the topside metal contact versus bias was measured directly using a microthermocouple probe. Finite element modeling showed good agreement with measured surface temperatures. The simulations indicate that, prior to the onset of lasing in the bottom active region, nonradiative recombination heating in the bottom active region significantly heats the (lasing) top active region, leading to a reduction in the differential slope efficiency of the bipolar cascade laser.