| Energy levels and the energy shift of free Polarons in wurtzite MgyZn1-yO/MgxZn1-xO parabolic quantum wells are investigated in the paper. The anisotropy of the dielectric constant, the electron effective mass and the phonon frequency in wurtzite structure are considered. The ground state energy, the first excited state energy, the transition energy and the effect of electron-phonon interaction on the ground state energy of polarons as functions of well width d and composition x in wurtzite MgyZn1-yO/ MgxZn1-xO parabolic quantum wells are given by using two unitary transformations of the system Hamiltonian. And the results are compared with the corresponding values of the square quantum well. The effect of the electron-optical phonon (confined phonon modes CF. and half-space phonon modes HS) interaction on the energy of the system is significant. The effect of the electron-confined phonon interaction on the energy level increases with increasing the quantum well width, while the effect of the electron-half space phonon interaction on the energy level decreases with increasing the quantum well width. Therefore. half-space phonons play an important effection in a narrow well, while confined phonons play an important effection in a wide well. The effects of symmetry phonon modes is larger than the effects of antisymmetric phonon modes. The whole contributions of confined phonons and half-space phonons to the ground state energy are about from 63meV to 80meV,and the values are larger than the results of AlxGa1-xAs/AlyGa1-yAs parabolic quantum wells. The ground state energy, the first excited state energy and the transition energy of polarons in wurtzite MgyZn1-yO/ MgxZ1-xO finite parabolic quantum wells increase with increasing composition x when the well width is fixed value. With increasing composition x, the growth rate of the energy and transition energy are relatively large for a small well width, while the growth rate of the energy and transition energy are relatively small for a large well width. The polaron energy shift caused by electron-confined optical phonons increase with increasing composition x, while the polaron energy shift caused by electron-half-space optical phonons decrease with increasing composition x. The polaron energy shift caused by electron-confined optical phonons and electron-half-space optical phonons decrease slowly with increasing composition x. The results are caused by the effect of confination in the quantum well. In the process of changing x, CF (including symmetric and anti symmetric) phonons increase and HS (symmetric and anti symmetric) phonons decrease.The polaron energy shift in wurtzite MgyZ1-yO/MgxZn1-xO parabolic quantum wells is larger, so the electron-optical phonon interaction can not be ignored when discussing electronic state energy levels. |
