Proton-implanted shallow-ridge quantum-cascade laser

We demonstrate a shallow-ridge quantum-cascade laser (QCL) with performance comparable or better than that of deep-ridge QCLs fabricated from the same wafer. The shallow-ridge QCL emits at ≈4 μm with a 4.6-4.8 kA/cm² threshold current density at room temperature which is similar to the deep-ridge QCL. At the same time the shallow-ridge QCL shows a better temperature stability, T₀=160 K, than the deep-ridge QCL, with T₀=120 K. The increase in the characteristic temperature of the shallow-ridge laser compared to the deep-ridge laser results from the improved heat dissipation out of the laser ridge through the lateral heat flow. Lateral spreading of the injection current-usually a drawback of shallow-ridge lasers-is suppressed by proton implantation into the strain-compensated InGaAs-AlAs active region layers on either side of the ridge. In contrast to the case of In_0.53Ga_0.47As layers and of In_0.53Ga_0.47As-In_0.52Al_0.48As heterostructures lattice matched to InP, the proton implantation of strain-compensated In_0.73Ga_0.27As-AlAs heterostructure on InP creates deep (180 meV) carrier traps, resulting in this material being electrically insulating even at room temperature.