Impact of Cascade Number on the Thermal Properties of Broad-Area Quantum Cascade Lasers

In this article the operation and thermal conductance of a series of quantum cascade lasers (QCLs) emitting at 4.6 mu m grown with between 5 and 30 cascades in the active region is analyzed. A reduced number of cascades, but with fixed active region design, results in larger threshold current density but lower threshold power density. An analysis of the temperature gradient in the active region implies that for continuous-wave QCL operation, using fewer than 15 cascades in the active region is advantageous, especially for broad-area structures. We demonstrate a QCL with 10 cascades operating in continuous-wave mode at room temperature emitting 0.9 W from a 4 mm x 30 mu m stripe.