Tailoring of the nonlinear optical rectification in vertically and laterally coupled InxGa1-xAs/GaAs quantum dots for Tera-hertz applications: Under In/Ga inter-diffusion, indium segregation, and strains effects

Abstract

We numerically investigate the Nonlinear Optical Rectification (NOR) of two laterally coupled lens-shaped InxGa1-xAs/GaAs quantum dots and two layers of InxGa1-xAs/GaAs coupled QDs along the growth axis. In addition, we have examined the impact of applying an external electric field, hydrostatic pressure, and temperature on the NOR under indium segregation inside the wetting layer (WL) and In/Ga inter-diffusion in the QD region. The three-dimensional Schrödinger equation (3D) is solved numerically using the finite difference method (FDM) within the framework of the effective mass. We have used the compact density matrix formalism to compute the NOR coefficient. Our findings reveal that the indium segregation and inter-diffusion phenomena significantly affect the NOR coefficient and should be considered appropriately. It is also found that the lateral and vertical coupling thicknesses significantly impact the NOR coefficient, and the structure under investigation has a resonant behavior in the terahertz domain (0.1–10 THz). Moreover, obtained results reveal that the applied electric field orientation and intensity significantly affect the NOR magnitude. Therefore, the NOR intensity reaches the maximum value, χ(0)(2)=50.10-7m/V, for a negative applied electric field, F = −10 kV/cm. Additionally, it was shown that the increase in the hydrostatic pressure shifts the NOR spectrum to higher energies (blue-shift), whereas increasing temperature has the contrary effect. It is worth noting that the NOR magnitude and its attributed resonance energy can be adjusted for THz devices with a good choice of the external factors mentioned above.