Heterostructures of quantum-cascade lasers with nonselective overgrowth by metalorganic vapour phase epitaxy

The possibility of fabrication of 4.6 $\mu$m spectral range quantum-cascade laser heterostructures by molecular-beam epitaxy technique with non-selective overgrowth by the metalorganic vapour-phase epitaxy is shown. The active region of the laser was formed on the basis of a heteropair of In$_{0.67}$Ga$_{0.33}$As/In$_{0.36}$Al$_{0.64}$As solid alloys. The waveguide claddings are formed by indium phosphide. The results of surface defects inspection and X-ray diffraction analysis of quantum-cascade laser heterostructures allow to conclude that the structural quality of the heterostructures is high and the estimated value of the root mean square surface roughness does not exceed 0.7 nm. Lasers with four cleaved facets exhibit lasing at room temperature with a relatively low threshold current density of the order of 1 kA /cm$^2$.