Failure Analysis of High-Power (One-Watt) Room-Temperature Continuous Wave MOCVD Quantum Cascade Lasers

Mid-infrared quantum cascade lasers (QCLs) are a growing industry and are being introduced into the marketplace primarily for low-output-power operation. High-power (> 1 W) continuous wave (CW) QCLs are expected to become commercially viable as they become more efficient and the necessary thermal dissipation requirements are achieved. However, there is a relative lack of knowledge regarding the degradation and failure mechanisms of QCLs under high power CW operation [1,2]. QCLs are expected to have different degradation and failure modes than diode lasers, because nonradiative recombination at the facets is not an issue. To push towards wider commercial adoption, lifetesting and failure analyses of high-power QCLs are performed. Previously reported QCL lifetests were carried out at relatively low output powers (∼200 mW) and revealed activation energies as high as 1.2 eV, with the primary failure mechanism being reported to be oxidation of the front facet [3]. Here, we report on initial constant-power lifetest studies of QCLs emitting at λ ∼ 5.0 μm and operating at 5 times the output power previously reported (i.e. at 1W CW). To mitigate the failure mechanism previously observed and improve device output, both facets have coatings: a high-reflectivity (HR) back-facet coating and a 14% low-reflectivity (LR) front-facet coating. The devices are mounted epi-side-down on copper with indium and tested under constant-power operation in a controlled environment.