Self-consistent design of strain-compensated InGaAs/InAlAs quantum cascade laser structures: Towards short wavelengths

We designed InxGa1−xAs/InyAl1−yAs quantum cascade laser (QCL) structures, based on the four-quantum well active region operating at λ ~ 2.8−3.3 μm in terms of an objective function, i.e., zgL(l − tl/tul)tu, related to the optical gain, including dipole matrix element (zUL) and population inversion between electron transitions. For shorter wavelength emission, the higher conduction band discontinuity (ΔEC) was achieved by changing the In mole fraction of InxGa1−xAs/InyAl1−yAs strain-compensated layers. The use of strain-compensated In0.72Ga0.28As/In0.3Al0.7As pair (i.e, ΔEC = 857 meV) leads to the shortest wavelength up to λ ~ 2.84 μm with τ43 = 3.96 ps, τ4 = 1.21 ps, τ3 = 0.55 ps and z43 = 0.57 nm under an electric field of 94 kV/cm.