The role of electron temperature in the leakage current in QCLs and its impact on the quantum efficiency

摘要

We have recently described a method to analyze the leakage current (J_(leak)) in quantum-cascade lasers (QCLs) for carriers scattering into higher minibands due to LO-phonon absorption. In his presentation we analyze J_(leak) due to elastic scattering. We illustrate how at low temperature, when inelastic scattering is negligible, this current becomes significant for devices operating at high electron temperatures. Measuring J_(leak) above threshold we are able to investigate the effect of electron temperature on the differential quantum efficiency. This procedure is supported by a self-consistent calculation of the rate equations based on a phenomenological scattering-rate model. We apply our approach and measure J_(leak) above threshold as a function of electron temperature for a QCL emitting near 5.4 μm operated at a low duty cycle and a heat sink temperature of 80 K. This current is then modeled using a thermally activated, electron temperature-driven, scattering model based on intersubband interface roughness scattering. As a result, a reduction in the upper laser state population by ～35% is estimated due to the effect of increased electron temperature. A decrease of the quantum efficiency of ～ 80% is estimated for an electron temperature of 400 K.