Analysis of TEM image of quantum cascade laser heterostructure grown by metalorganic vapour-phase epitaxy

The transmission electron microscopy (TEM) image of a quantum cascade heterostructure was analyzed. A heterostructure containing 185 periods and four quantum wells GaAs/Al$_{0.15}$Ga$_{0.85}$As in each period was grown by MOVPE. Different composition spreading laws (normal, exponential and asymmetric exponential) have been used to reveal the differences in the composition deviation at the interface “barrier/quantum well” and “quantum well/barrier” when interpolating the experimental hetero-interface profile. The effect of finite sample thickness on the composition fluctuation characteristics has been theoretically investigated and spectra and autocorrelation functions of composition fluctuations have been obtained. Estimates of the thickness of hetero-interface roughness and its correlation length have been carried out.