Effect of Quantum Barrier Thickness on the Optical Properties of Triple Triangular GaAs/AlGaAs Quantum Wells

This study investigates the electronic and optical properties of a GaAs/AlxGa1-xAs triple triangular quantum well (QW) structure, focusing on the 2-4 and 3-4 intersubband transitions. By varying the right barrier (RB) thickness from 0 to 6 nm, the impact on wave function localization, energy levels, dipole moment matrix elements, absorption coefficients, and refractive index changes was analyzed using a finite element-based Schrödinger solver. Quantitative results indicate that increasing the RB breaks the symmetry of the potential, enabling the 2-4 transition and causing variations in absorption coefficients, which peak at 4 nm before declining. The 3-4 transition exhibits a higher and more stable total absorption coefficient compared to the 2-4 transition, ranging from 1100 to 1125 cm⁻¹. Additionally, the total refractive index changes for the 3-4 transition remain constant (±0.006 to ±0.009), while the 2-4 transition shows more variation (±0.001). Qualitatively, the 3-4 transition's stability and minimal energy difference from the 2-4 transition make it a more promising candidate for terahertz device applications, particularly where RB thickness constraints are present. These findings underscore the importance of barrier engineering in optimizing QW-based devices for advanced semiconductor application.