Combined effects of interdiffusion, electric field, pressure, and temperature on linear and nonlinear intersubband optical absorption in GaAs/AlGaAs multiple quantum wells for terahertz applications

In this work, a theoretical investigation of asymmetric GaAs/AlGaAs's electrical structure and intersubband optical characteristics for terahertz applications is presented. The Schrödinger equation within the effective-mass approximation is solved using the finite-difference method (FDM) to determine the confined electronic states, and the density-matrix formalism is used to evaluate the linear (1), third-order nonlinear (3), and total () optical absorption coefficients. In addition, a comprehensive investigation is conducted of the combined effects of temperature (T), incident optical intensity (I), hydrostatic pressure (P), external electric field (F), atoms interdiffusion, and structural periodicity. The findings demonstrate that through interface smoothing and the quantum-confined Stark effect, interdiffusion and the electric field efficiently adjust the confinement potential (V), electronic states, transition energies, and absorption spectra. While hydrostatic pressure decreases the absorption intensity, temperature increases it. Also, a greater number of quantum-well periods (Np) results in a redshift and broadening of the absorption spectra, whereas increasing the optical intensity causes nonlinear saturation. Moreover, an excellent agreement between the theoretical model and the experimental photoluminescence (PL) spectrum is obtained, with transition energy variations less than 5 meV. These findings offer practical recommendations for design and optimization of nonlinear optoelectronic devices in the terahertz (THz) field.