Comprehensive analysis of nonlinear optical responses in GaAs/AlGaAs nanolayer structures with tunable quantum wells

This study presents a comprehensive theoretical investigation of three-layered GaAs/AlGaAs semiconductor nanoplatelets with tunable quantum well thicknesses for optoelectronic applications. Using a compact density-matrix approach combined with numerical solutions of the Schrödinger equation, we calculate subband energies, dipole matrix elements. Then, five key nonlinear optical responses, nonlinear optical rectification, second harmonic generation, third harmonic generation, total optical absorption, and relative refractive index change are derived analytically. Our results reveal that adjusting the well and barrier widths provides a tuning the optical absorption coefficients, refractive index changes, and harmonic generation responses. In particular, we demonstrate that the interplay between confinement length and barrier thickness leads to shifts in resonant peaks and variations in the amplitude of nonlinear responses. We study these five properties together in this specific structure. We showed that varying the structure parameters provides precise and differential control over the resonant peaks and amplitudes for all five coefficients. These results establish a direct link between structural design and nonlinear performance, offering guidance for engineering nanoscale optoelectronic devices. The findings highlight both the novelty and the technological relevance of employing tunable GaAs/AlGaAs nanolayers as versatile platforms for photonic and quantum applications.