The Effect Of Polaron In Wurtzite GaN/Al_x Ga_1-x N Quantum Well

The effect of polaron, the electron and confined-optical-phonon interaction on energy are calculated in the wurtzite nitride quantum well by using modified Lee-Low-Pines (LLP) variational method in the paper. The anisotropy of the optical-phonon modes and the phonon frequency changing with vectors are considered in the wurtzite quantum well. The ground state energy, first excited state energy and the transition energy of the polaron in wurtzite GaN/AlxGa1-xN and InxGa1-xN/GaN quantum well changing with the quantum well width and composition are given.The results show that the ground state energy, first excited state energy and the transition energy of polaron in wurtzite GaN/AlxGa1-xN and InxGa1-xN/GaN quantum well decrease with increasing the well width, and the energy decrease rapidly at a narrow well, then decrease slowly and finally approach to the three-dimensional material value of GaN and InN at a large well width.The energy of polaron in wurtzite quantum well is smaller than the polaron energy in zinc-Blende quantum well, the contribution of the electron-phonon interaction on the polaron ground state energy in former material is larger than the contribution of the latter. It is mainly due to the reasons of the anisotropy of wurtzite and the difference of parameters between wurtzite and zinc-Blende materials. The results also show that the ground state energy,first excited state energy and the transition energy of polaron in the wurtzite GaN/AlxGa1-xN and InxGa1-xN/GaN quantum well increase with increasing the composition (Al or In),and there is a sharp change at a narrow well width, and the change becomes slowly at a large well width. The results also show that the electron - phonon interaction on the contribution of polaron energy in GaN/Al0.3Ga0.7N and In0.3Ga0.7N/GaN quantum well is much greater and larger than the corresponding values in GaAs/Al0.3Ga0.7As quantum well. Meanwhile, several different methods for calculating polaron energies by using LLP method are analyzed and discussed.