The surface morphology of a buffer template is an important factor in the heteroepitaxial integration of optoelectronic devices with a significant lattice mismatch. In this work, InP-based long-wave infrared (~8 µm) emitting quantum cascade lasers with active region designs lattice-matched to InP were grown on GaAs and Si substrates employing InAlGaAs step-graded metamorphic buffer layers, as a means to assess the impact of surface roughness on device performance. A room-temperature pulsed-operation lasing with a relatively good device performance was obtained on a Si template, even with a large RMS roughness of 17.1 nm over 100 µm2. Such results demonstrate that intersubband-operating devices are highly tolerant to large RMS surface roughness, even in the presence of a high residual dislocation density.
