Complex Dielectric Permittivity Extraction of Mid-Infrared Intersubband Quantum Cascade Structures

Designing next-generation optoelectronic devices necessitates a comprehensive understanding of the dielectric properties of anisotropic materials. This work introduces a novel approach to quantify intersubband transitions (ISBTs) in mid-infrared quantum cascade structures (QCSs). Precise dielectric functions for both ordinary and extraordinary polarizations are determined using advanced ellipsometry combined with computational optimization techniques. The methodology integrates anisotropic parameterization, transfer matrix methods, and the Drude-Lorentz model, enabling accurate simulations of complex optical processes. By considering energy-dependent interactions and structural anisotropy, the proposed multi-step iterative technique effectively reduces discrepancies between theoretical and experimental ellipsometric values. The results validate the critical role of ISBTs-induced dichroism and birefringence in QCSs, evidenced by the strong agreement between measured and simulated optical constants. This framework establishes a robust basis for developing high-performance photonic devices, such as quantum cascade lasers, detectors, and mid-infrared sensing technologies, providing insights into the anisotropic dielectric properties of materials.