The Effect Of Interface Optical-phonon Modes To Polaron Energy In Wurtzite In_xGa_1-xN/GaN Quantum Well

The ground state energy, the first excited state energy and the transition energy ofpolaron in wurtzite In_0.3Ga_0.7N/GaN and GaN/Al_0.3Ga_0.7N quantum well as functionsof well width and composition x are investigated by using modified Lee–Low–Pines（LLP） variational method in the paper. The effect of the electron-phononinteraction on the energy is discussed. The effects of the confined optical phononmodes, the interface optical phonon modes, and the anisotropy of optical phononfrequency are considered in the calculation. In order to compare, the correspondingresults in the zinc-blende quantum well are given. The results show that the groundstate energy, the first state energy and transition energy of polaron in In_0.3Ga_0.7N/GaNand GaN/Al_0.3Ga_0.7N quantum well decreases with increasing well width d, and finallyapproaches to the bulk value of In_0.3Ga_0.7N and GaN. The energy and transition energyof polaron in wurtzite quantum well are smaller than that in zinc-blende quantum well,and the contributions of the electron-phonon interaction to the energy of polaron inwurtzite quantum well are larger than that in zinc-blende quantum well. For example,for the well width d=20nm, the contributions in wurtzite In_0.3Ga_0.7N/GaN andGaN/Al_0.3Ga_0.7N quantum well are about35meV、40meV, and in zinc-blendeIn_0.3Ga_0.7N/GaN and GaN/Al_0.3Ga_0.7N quantum well are about30meV、35meV. Fordifferent phonon modes, the contributions of the interface phonon modes on energy are larger than that of the confined modes for narrow wells, and the contributionsrapidly decrease with increasing the well width, and approach to zero. But thecontributions of the confined modes rapidly increase with increasing the well width,and the contributions are larger than that of the interface modes at certain well width,and finally approach to total contributions. The contribution of the electron-phononinteraction to the energy of polaron in nitride(In_0.3Ga_0.7N/GaN and GaN/Al_0.3Ga_0.7N)quantum well is much larger than that in GaAs/Al_xGa_1-xAs quantum well （about2.5meV）. Therefore, the electron-phonon interaction should be considered forstudying the energy of polaron in nitride quantum well structure. The results alsoshow that the ground state energy, the first excited state energy and the transitionenergy of polaron in In_xGa_1-xN/GaN and GaN/Al_xGa_1-xN quantum well increases withincreasing the composition x, and it is more visible in narrow well, but it is slowly inlarge well width. Meanwhile, the contribution of electron-phonon interaction to thepolaron energy in GaN/Al_xGa_1-xN quantum wells increases with increasing the Alcomposition, but the case is contrary in In_xGa_1-xN/GaN quantum wells.