Thermal annealing of lattice-matched InGaAs/InAlAs Quantum-Cascade Lasers

We describe the evolution of optical power, threshold current, and emission wavelength of a lattice-matched InGaAs/InAlAs Quantum-Cascade Laser (QCL) emitting at 13 μm grown by gas-source molecular-beam epitaxy under thermal annealing. Pieces from the same 2-in wafer were annealed at 600 °C, 650 °C, or 700 °C for 1 h; one control piece remained unannealed. No change in threshold current and emission wavelength was observed. The slope efficiency and maximum emission power increase for the 600 °C anneal, but higher annealing temperatures resulted in degraded performance. This result stands in contrast with the observation that strain-compensated structures cannot withstand annealing temperature of 600 °C. Useful information for post-growth processing steps and the role of interface roughness in QCL performance are obtained.