Free polaron energy levels in AlyGa1-yN/AlxGa1-xN triangle quantum well structures

摘要

In this work, a variational method is used to examine the problems relevant to the free polaron energy spectrum in a wurtzite AlyGa1-yN/AlxGa1-xN triangle quantum well structure. The numerical calculations for the ground state energy, transition energy and polaron energy shifts as the functions of well-width d and composition x are carried out by considering the anisotropies of the parameters, such as the optical phonon frequency, dielectric constant and electron effective mass, as well as their observed changes with coordinate z in this system. The research results show that the polaron energy shift caused by the electron optical phonon interaction is large, and leads to an obvious energy decrease in the AlyGa1-yN/AlxGa1-xN triangular quantum well structure. The contribution of the confined phonon is found to increase with the increasing of the well-width and composition x, while that of the half space phonon is observed to decrease with the increasing of the well-width and composition x. The total contribution of the phonon increases with the increasing composition x, while a minimum is found to occur to the total contribution of the phonon during the decreasing process with the well-width. As the d increases, the free polaron energies and transition energies decrease. Meanwhile, with the increasing of the composition x, the energy and transition energy are found to be increased. In the AlyGa1-yN/AlxGa1-xN triangular quantum well structure, the trends of the free polaron energy, transition energy and polaron energy shifts with the well-width and composition x are found to be similar to those in the GaN/AlxGa1-xN square quantum well structure. However, the corresponding values in the triangular quantum well structure are obviously greater than those in the square quantum well structure.