Improved Continuous Wave Operation of Quantum Cascade Lasers with Epitaxial-Side Heat-Sinking

First results on the epilayer-side mounting of quantum cascade (QC) lasers are presented. Operated in continuous wave (cw) mode, these lasers are superior to substrate-bonded devices. The maximum cw temperatures is raised by 20K (up to 175K), and at comparable heat sink temperatures the performance with respect to threshold current, output power and slope efficiency is greatly improved for the epilayer-side mounted devices. QC-laser specific problems in the actual mounting procedures have been solved and are discussed in this letter, such as the high reflectivity coating of the back-facet and the front-facet cleaving after mounting. Modeling of the temperature distribution inside the QC-laser shows a strong temperature gradient within the active waveguide core, which partly explains the still low maximum cw operating temperatures.