Heterostructures for quantum-cascade lasers of the wavelength range of 7–8 $\mu$m

It is shown that molecular-beam-epitaxy technology can be used to fabricate heterostructures for quantum-cascade lasers of the wavelength range of 7–8 $\mu$m with an active region comprising 50 cascades based on a heterojunction of In$_{0.53}$Ga$_{0.47}$As/Al$_{0.48}$In$_{0.52}$As solid solutions. The optical emission is obtained using a quantum-cascade design operating on the principle of two-phonon resonance scattering. The properties of heterostructures were studied by the methods of X-ray diffraction and transmission electron microscopy, which showed their high quality with respect to the identical compositions and thicknesses of all 50 cascades. Stripe-geometry lasers made of these heterostructures exhibited lasing with a threshold current density below 1.6 kA/cm$^2$ at a temperature of 78 K.