Controlling the performance of GaAs–AlGaAs quantum-cascade lasers via barrier height modifications

A series of GaAs/AlGaAs quantum-cascade lasers has been studied in which the confinement of the upper lasing level is systematically varied. This is achieved by modifying the aluminum composition, and hence the height, of a single barrier in each active region. Increasing the height of the barrier increases the upper laser level lifetime, while decreasing the optical transition matrix element. We find an optimum barrier composition (Al0.4Ga0.6As), with the sample containing this barrier exhibiting a significantly improved low-temperature threshold current density (3.8 kA/cm2) and peak power output (∼800 mW) relative to previously reported GaAs-based quantum-cascade lasers. The temperature performance of all the samples is very similar, indicating that thermal activation of electrons from the upper laser level is not the dominant factor limiting high-temperature operation.