Buried-heterostructure mid-infrared quantum cascade lasers fabricated by non-selective regrowth and chemical polishing

A novel fabrication method of buried-heterostructure (BH) mid-infrared quantum cascade lasers (QCLs) by using non-selective regrowth of iron-doped indium phosphide (InP) (Fe:InP), around deeply etched laser ridges, via metal-organic chemical vapour deposition (MOCVD) and planarisation via chemical polishing is reported. Owing to better heat dissipation, the fabricated 4.75 μm emitting QCLs exhibit about three-fold enhancement in maximum output power under continuous-wave operation at room temperature (T = 20°C) compared with that from lasers without the regrown InP. The demonstrated fabrication method provides a more flexible route to realising BH QCLs by removing strict requirements on the etched-ridge sidewall profile, as well as on the physical dimensions of the dielectric mask for the regrowth via MOCVD. The method can be further employed for making large-emitting aperture, closely packed arrays of QCLs, with planarised geometry, for coherent-power scaling.