纤锌矿In0．19Ga0．81N／GaN量子阱中光学声子和内建电场对束缚极化子结合能的影响

Effects of optical phonon and built-in electric field on the binding energy of bound polarons in a wurtzite In_(0.19)Ga_(0.81)N/GaN quantum well

用改进的Lee-Low-Pines变分方法研究纤锌矿In0.19Ga0.81N/GaN量子阱结构中束缚极化子能量和结合能等问题,给出基态结合能、不同支长波光学声子对能量和结合能的贡献随阱宽和杂质中心位置变化的数值结果.在数值计算中包括了该体系中声子频率的各向异性和内建电场对能量和结合能的影响、以及电子和杂质中心与长波光学声子的相互作用.研究结果表明,In0.19Ga0.81N/GaN量子阱材料中光学声子和内建电场对束缚极化子能量和结合能的贡献很大,它们都引起能量和结合能降低.结合能随着阱宽的增大而单调减小,窄阱中减小的速度快,而宽阱中减小的速度慢.不同支声子对能量和结合能的贡献随着阱宽的变化规律不同.没有内建电场时,窄阱中,定域声子贡献小于界面和半空间声子贡献,而宽阱中,定域声子贡献大于界面和半空间声子贡献.有内建电场时,定域声子贡献变小,而界面和半空间声子贡献变大,声子总贡献也有明显变化.在In0.19Ga0.81N/GaN量子阱中,光学声子对束缚极化子能量和结合能的贡献比GaAs/Al0.19Ga0.81As量子阱中的相应贡献(约3.2—1.8和1.6—0.3 meV)约大一个数量级.阱宽(d=8 nm)不变时,在In0.19Ga0.81N/GaN量子阱中结合能随着杂质中心位置Z0的变大而减小,并减小的速度变快.随着Z0的增大,界面和半空间光学声子对结合能的贡献缓慢减小,而定域光学声子的贡献缓慢增大.

The energies and binding energies of the bound polarons in a wurtzite In0.19Ga0.81N/GaN quantum well are inves- tigated by means of a modified Lee-Low-Pines variational method. Contributions of ground state binding energies and different branches of a longwave optical phonon mode to the energies and binding energies of the bound polarons as a function of the well width and impurity center position are given. Effects of the anisotropy of phonon frequency and built-in electric field in the system on the energies and binding energies, and the electron and impurity center-optical phonon interaction, are included in the calculations. Results show that the contributions of optical phonons and built-in electric field to the ground state energy and binding energy of the bound polarons in a wurtzite In0.19Ga0.81N/GaN quantum well are very large, and result in the reduction of energy and binding energy. The binding energy decreases monotonically with increasing well width, and the speed of decrease is fast in the narrower well while the speed of decrease is slow in the wider well. Contributions of different branches of phonons to the energies and binding energies as a function of well width are different. In the narrower well, contributions of the confined phonon （withoud built-in electric field） are smaller than those of the interface and half-space phonons, while in the wider well, contributions of the confined phonons are larger than those of the interface and half-space phonons. Contributions of the confined phonon （with built-in electric field） become larger, whereas those of the interface and half-space phonons become smaller, and the total contribution of phonons also have obvious change. Contributions of these optical phonons to the ground state energies and binding energies of the bound polarons in In0.19Ga0.81N/GaN quantum wells are larger than the corresponding values （about 3.1--1.6 meV and 1.5--0.3 meV） of those in GaAs/Al0.19Ga0.81As quantum wells. The binding energies in In0.19Ga0.81N/GaN quantum wells decrease monotonically with increasing location Z0 of the impurity center for a constant well width d= 8 nm, and the decrease of speed becomes faster. As the position of the impurity center is increasing, the contributions of the the interface and half-space phonons decrease slowly, and those of the confined phonons increase slowly as well.