A particular behavior of levels energy evolution and theoretical study of the quantum probability distribution in GaAs/AlGaAs asymmetric stepped semiconductor quantum wells for terahertz optoelectronics

The study of the evolution of the energy levels as a function of the step layer’s width Lw2 in an asymmetric stepped quantum well AlxGa1-xAs/GaAs/AlyGa1-yAs/AlxGa1-xAsx=24%,y=14%, revealed a particular behavior, marked by the presence of plateaus within certain deep well’s width, Lw2, ranges. We initially computed the eigenenergies and eigenfunctions by numerically solving the Schrödinger equation. This was done within the effective mass and envelope function approximation, taking into account the influence of non-parabolicity. To explain the origin of the plateaus and their impact on intersubband transition energies, we determined the distribution of the probability density of the presence of the electron in each region of the stepped quantum well. The results of these calculations demonstrated that the electron's probability density is higher in the step well than in the deep one, particularly for electrons with energy levels above 113.47 meV. This elevation in probability density exhibits maximum values that remain nearly constant within specific Lw2 domains, providing an explanation for the observed energy plateaus. Such plateaus allow more energy tunability and thus open up additional possibilities for applications in the THz domain either in the linear or nonlinear optics.