多层球形核壳量子点中光学振动模的三元混晶效应

Ternary Mixed Crystal Effect of Optical Vibration Modes in Multilayer Spherical Core-Shell Quantum Dots

考虑三元混晶的"单模"与"双模"性,利用介电连续模型和改进的无规元素等位移模型,研究了含三元混晶的多层球形核壳量子点中的光学声子模.选取InN/InxGa1-xN/InN和ZnSe/ZnSxSe1-x/ZnSe两种核壳结构进行了数值计算,其中InxGa1-xN为单模型三元混晶,ZnSxSe1-x为双模型三元混晶,给出了两种结构中声子模频率随混晶组分、量子点尺寸以及角量子数的变化关系.结果表明,InN/InxGa1-xN/InN和ZnSe/ZnSxSe1-x/ZnSe结构中分别存在着5支和7支界面/表面光学声子模,且均具有特殊的混晶效应,具体表现在各支声子模的频率对组分x有不同的依赖关系.当组分x>0.8时,在ZnSe/ZnSxSe1-x/ZnSe结构中,模6、7重合为一支.同时发现各支声子模的频率对内壳层厚度γ1和较小的量子数l的依赖性较强.

Considering the one-mode and two-mode behaviors of ternary mixed crystals(TMCs),the optical phonon modes in multilayer spherical core-shell quantum dots containing of TMCs are discussed based on the dielectric continuum approach and modified random-element-isodisplacement model.Numerical calculations on the InN/InxGa1-xN/InN("one-mode" TMC) and ZnSe/ZnSxSe1-x/ZnSe("two-mode" TMC) core-shell structures have been performed.A detailed discussion of optical phonon mode frequencies as functions of components x and quantum dot size and quantum number l are given.The results show that there are five and seven branches of interface/surface optical phonon modes in InN/InxGa1-xN/InN and ZnSe/ZnSxSe1-x/ZnS structures,respectively.The mixed crystal effect has different influence on optical phonon mode frequencies.When x>0.8,modes 6 and 7 overlap into one mode in the ZnSe/ZnSxSe1-x/ZnSe structure.It is also found that the phonon frequencies are strongly dependent on the inner shell thickness γ1 and smaller quantum number l.