Design considerations for λ ∼ 3.0- to 3.5-μm-emitting quantum cascade lasers on metamorphic buffer layers

Quantum cascade lasers (QCLs) that employ metamorphic buffer layers as substrates of variable lattice constant have been designed for emission in the 3.0-to 3.5-mu m wavelength range. Theoretical analysis of the active-region (AR) energy band structure, while using an 8-band k.p model, reveals that one can achieve both effective carrier-leakage suppression as well as fast carrier extraction in QCL structures of relatively low strain. Significantly lower indium-content quantum wells (QWs) can be employed for the AR compared to QWs employed for conventional short-wavelength QCL structures grown on InP, which, in turn, is expected to eliminate carrier leakage to indirect-gap valleys (X, L). An analysis of thermo-optical characteristics for the complete device design indicates that high-Al-content AlInAs cladding layers are more effective for both optical confinement and thermal dissipation than InGaP cladding layers. An electroluminescence-spectrum full-width half-maximum linewidth of 54.6 meV is estimated from interface roughness scattering and, by considering both inelastic and elastic scattering, the threshold-current density for 3.39-mu m-emitting, 3-mm-long back-facet-coated QCLs is projected to be 1.40 kA/cm(2). (C) The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License.