Proton implantation for electrical insulation of the InGaAs/InAlAs superlattice material used in 8-15 μm-emitting quantum cascade lasers

We demonstrate the conversion of lattice-matched InGaAs/InAlAs quantum-cascade-laser (QCL) active-region material into an effective current-blocking layer via proton implantation. A 35-period active region of an 8.4 μm-emitting QCL structure was implanted with a dose of 5 × 10¹⁴ cm⁻² protons at 450 keV to produce a vacancy concentration of ∼10¹⁹cm⁻³. At room temperature, the sheet resistance, extracted from the Hall measurements, increases by a factor of ∼240 with respect to that of an unimplanted material. Over the 160-320 K temperature range, the activation energy of the implanted-material Hall sheet-carrier density is 270 meV. The significant increase in room-temperature sheet resistance indicates that upon implantation deep carrier traps have been formed in the InAlAs layers of the superlattice. Fabricated mesas show effective current blocking, at voltages ≥10 V, up to at least 350 K. Thus, the implanted InGaAs/InAlAs superlattices are highly resistive to at least 350 K heat sink temperature. Such implanted material should prove useful for effective current confinement in 8-15 μm-emitting InP-based single-emitter QCL structures as well as in resonant leaky-wave coupled phase-locked arrays of QCLs.