Catastrophic Optical Damage Mitigation in Quantum Cascade Lasers by Facet Disordering

Quantum cascade laser optical output power is limited by laser facet catastrophic optical damage (COD). In edge-emitting semiconductor lasers COD is a thermal runaway process wherein the front facet of the laser heats under high power operation. This facet heating reduces the semiconductor bandgap which increases the optical absorption and also increases the electrical injection current in the facet region. The increase in facet temperature accelerates crystallographic defect propagation. The end result of this thermal runaway is laser facet burnout. Whereas a variety of facet coatings have been investigated, the most robust method of reducing COD has been that of quantum well intermixing whereby lattice disordering is used to convert the laser facet regions to material with a larger bandgap than that of the bulk laser material. When properly designed, this can mitigate thermal runaway. Phase I will theoretically analyze facet heating and thermal runaway by COD for edge-emitting QCLs, and will then establish a candidate quantum well intermixing procedure based on prior successful COD reduction in commercial edge-emitting III-V compound semiconductor lasers. Phase II will then institute this procedure on mid-IR QCLs and measure the resulting performance improvement under high power operating conditions.