Impurity States And Polaron Effect In The Strain GaN/Ga_xAl_1-xN Cylindrical Quantum Dot

Within the framework of the effective-mass approximation, hydrogenic impurity states and the polaron effect in the strain GaN/Al_xGa_1-xN cylindrical wurtzite quantum dot are investigated by considering the influence of infinite barriers.Firstly, within effective-mass approximation, we have calculated the binding energy of hydrogenic impurity state by a vanational approach in the strain GaN/Al_xGa_1-xN cylindrical quantum dot, including the strong built-in electric field effect due to the spontaneous and piezoelectric polarizations. The numerical results showed that the built-in electric field decreases the binding energy of impurity state, since moving the electron and the impurity to reverse direction. The influence of the Al content was also considered. It is found that the binding energy of impurity state decreases when the Al content is increasing. Moreover, for quantum dot height L<2nm, the change of the binding energy is very small with the Al content variety.Then, a variational method is adopted to investigate the polaron effect in the strain GaN/Al_xGa_1-xN cylindrical quantum dot by taking the uniaxial anisotropy and the built-in electric field into account. The numerical results show that the polaron effect obviously decreases the binding energy. Further, the contribution of LO-like phonon to the binding energy is dominant. At the same time, the binding energy slightly decreases with the Al content increasing, and the change of the binding energy is inconspicuous with the anisotropy angle variety.