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 /spl ap/4 /spl mu/m with a 4.6-4.8 kA/cm/sup 2/ 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, T/sub 0/=160 K, than the deep-ridge QCL, with T/sub 0/=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/sub 0.53/Ga/sub 0.47/As layers and of In/sub 0.53/Ga/sub 0.47/As-In/sub 0.52/Al/sub 0.48/As heterostructures lattice matched to InP, the proton implantation of strain-compensated In/sub 0.73/Ga/sub 0.27/As-AlAs heterostructure on InP creates deep (180 meV) carrier traps, resulting in this material being electrically insulating even at room temperature.