Shallow Impurity States in Ternary Mixed Crystals

利用微扰－变分法研究了极性三元混晶中束缚在浅库仑杂质中心的极化子．采用改进的无序元胞独立位移模型和有效声子模近似，计及电子和两支光学声子的相互作用，导出了极化子基态能量和束缚能量随组分变化的解析解，分析了声子屏蔽、质量重整化和自陷效应．对若干三元混晶的数值计算结果表明：声子屏蔽效应占主要作用；电子声子的相互作用减小了束缚极化子的束缚能．发现声子对束缚能的贡献随组分的变化是非单调的．讨论了有效声子模方法的有效性和适用范围

Shallow Impurity States in Ternary Mixed Crystals

Polaron bound to a shallow Coulomb impurity center in a polar ternary mixed crystal A x B 1-x C is studied by a perturbation variation method.The interaction between an electron and two branches of longitudinal optical phonon modes is taken into account by using the modified random element isodisplacement model and a so called effective phonon mode approximation method.The analytic expressions for the ground state energy and the binding energy of the polaron as functions of the composition x are obtained.The phonon screening,mass renormalization and self trapping effects are analyzed.The numerical results for several ternary mixed crystals show that the phonon screening effect is dominant and the binding energies of bound polarons are generally reduced by the electron phonon interaction.A non monotonous dependence of the phonon contributions to the binding energies on the composition x is found.The validity of the effective phonon mode approximation method is discussed.