Heterostructures of quantum-cascade laser for the spectral range of 4.6 $\mu$m for obtaining a continuous-wave lasing mode

The method of molecular-beam epitaxy was used to fabricate an elastically balanced heterostructure of a quantum-cascade laser for the spectral range of 4.6 $\mu$m based on a heteropair of solid alloys, In$_{0.67}$Ga$_{0.33}$As/In$_{0.36}$Al$_{0.64}$As, and indium phosphide layers serving as waveguide cladding layers. An X-ray diffraction analysis demonstrated the high uniformity of the composition and thickness of layers in cascades of the heterostructure over the substrate area. Lasers with four cleaved facets show lasing at room temperature at a wavelength close to 4.6 $\mu$m with a comparatively low threshold current density of 1.1 kA/cm$^2$.