变分方法研究ZnO量子点中激子的基态特性

ZnO是一种新型宽禁带直接带隙Ⅱ-Ⅵ族半导体材料,室温激子束缚能高达60meV,远大于室温热离化能(26meV),因此ZnO是适于室温或更高温度下使用的高效紫外光电材料。ZnO半导体量子点材料与体材料相比具有崭新的光电特性,特别在紫外激光器件方面,与ZnO的激子特性密切相关,因此理论上对ZnO量子点中激子的基态特性进行研究就显得十分必要。采用有效质量近似(EMA)方法,提出新的比较简单的尝试波函数,对ZnO量子点中激子的基态特性进行了计算。计算结果与实验结果基本吻合,说明我们的计算结果比较真实、有效。对变分参数K_e、K_h,归一化常数N_e、N_h以及波函数ψ随粒径变化关系进行了计算。计算结果表明,当量子点半径较小(r≤4.0a_B)时,激子的波函数ψ变化非常迅速,而由于此时量子点具有很大的比表面积,因此量子点所处的环境、体内的缺陷、杂质会对其产生非常强烈的影响,同时其表面(界面)的介质会对其基态特性产生影响,因此对量子点进行有效的修饰与掺杂以减少其表面缺陷及表面悬键,减少无辐射复合与界面发射是非常必要的。

Study the Ground State Properties of Exciton in ZnO Quantum Dots by Variational Method

ZnO is a wide direct band gapⅡ-Ⅵ semiconductor material with a large exciton binding energy of 60 meV at room temperature,more larger than the ionization energy at room temperature(26 meV),so ZnO is a suitable high efficient ultraviolet material.ZnO quantum dots has unique photoelectric properties,especially can be used in UV laser devices related with the exciton characteristic,therefore, it is very important to study the ground state properties of exciton of ZnO quantum dots in theory.We compared the calculation results with the experiment values that indicate the new trial wave function is right.We also calculated the variation parameter K_e and K_h,the normalization constant N_e and N_h as functions of r,and the trial wave function ψ as functions of a_B.The results indicate when the radius of the quantum dot is very small(r≤4.0a_B),the trial wave function ψ will have a rapid change.And meanwhile the quantum dot will have a larger surface to volume ratio.So the surroundings,the defects and the purities will have strong effects on the ground state properties of the quantum dot,while the medium on the surface(or the interface) will have effects too.Thus,it is very important to reduce the defects and the dangling bonds on surface,eliminate the non-radiative recombination and the surface(the interface) emission by effective doping and modifying.