The emission wavelength of quantum cascade lasers can potentially be continuously tuned from the short (2µm) to the long (15µm) infrared, making them an ideal candidate for infrared emitters in a region where materials with the appropriate gap are scarce. The challenge with QCLs lies in the complexity of the epitaxial structure. Indeed, in a typical InGaAs/InAlAs/InP structure the active region is often comprised of thirty stages, each stage containing an alternation of twenty or more InGaAs wells and InAlAs barriers, the thicknesses of which range between 7 and 40 Angstrom. Properly optimizing the epitaxial process therefore requires feedback on the thickness and, most importantly, the composition of each individual well and barrier in the layer, as even small deviations can make or break the end device. Currently, even in the most advanced transmission electron microscopes, equipped with state of the art EDX systems it is not possible to obtain quantitative information on the composition of layers that are thinner than 15 Angstrom. Quantifying the chemical information in the Z-Contrast of HAADF images  therefore provides the only solution to obtain the kind of quantitative feedback required for QCLs. The present paper discusses how to obtain such chemical mappings in InGaAs/InAlAs QCLs by combining HAADF-STEM, EDX and also X-ray Diffraction and how the information collected from these mappings is used to optimize the QCL structure . The paper also discusses how this information is fed to numerical models to model the performance of the end device and optimize the QCL design. Finally, the paper forays into the quantification of the contrast of single atomic columns, ultimate step in the analysis.
 K. Pantzas, G. Patriarche, D. Troadec, S. Gautier, T. Moudakir, S. Suresh, L. Largeau, O. Mauguin, P. L. Voss, and A. Ougazzaden, Nanotechnology, 23, 455707 (2012)
 K. Pantzas, G. Beaudoin, G. Patriarche, L. Largeau, O. Mauguin, G. Pegolotti, A. Vasanelli, A. Calvar, M. Amanti, C. Sirtori, and I. Sagnes, Semiconductor Science and Technology, accepted for publication (2016)
To cite this abstract:Konstantinos Pantzas, Gilles Patriarche, Ludovic Largeau, Maria Amanti, Angela Vasanelli, Carlo Sirtori, Grégoire Beaudoin, Isabelle Sagnes; Quantification of the HAADF contrast from the nanometer scale down to the single atomic column: application to quantum cascade lasers. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/quantification-of-the-haadf-contrast-from-the-nanometer-scale-down-to-the-single-atomic-column-application-to-quantum-cascade-lasers/. Accessed: January 21, 2022
EMC Abstracts - https://emc-proceedings.com/abstract/quantification-of-the-haadf-contrast-from-the-nanometer-scale-down-to-the-single-atomic-column-application-to-quantum-cascade-lasers/