Suppression of carrier leakage in 4.8 [micrometre] - Emitting quantum cascade lasers

Abstract

In this work we show that by using both deep quantum wells and tall barriers in the active regions of quantum cascade (QC)-laser structures and by tapering the conduction-band edge of both injector an extractor regions one can significantly reduce the leakage of the injected carriers. Threshold-current, Jth and differential-quantum efficiency, etad characteristic temperatures, T0 and T1, values as high as 278 K and 285 K are obtained to 90 °C heatsink temperature, which means that Jth and etad vary ~ 2.5 slower over the 20-90 °C temperature range than in conventional QC devices. Modified equations for Jth and etad are derived. In particular, the equation for etad includes, for the first time, its dependence on heatsink temperature. A model for the thermal excitation of injected carriers from the upper lasing level to upper active-region energy states from where they relax to lower active-region energy states or get scattered to the upper Gamma miniband is employed to estimate carrier leakage. Good agreement with experiment is obtained for both conventional QC lasers and deep-well (DW)-QC lasers.