Impurity And Exciton States In Strained Core-shell Spherical Quantum Dots And Effects Of Hydrostatic Pressure

Under the continuum dielectric model and effective mass approximation,the binding energies and optical properties of impurity states and exciton states in strained core-shell spherical quantum dots are theoretically studied by variational method.Firstly,the variation of the impurity binding energy and the photoionization cross section of InxGa1-xN/ZnSnN2 core-shell spherical quantum dots with the size of quantum dots and different impurity positions under strain are studied and compared with the results without the strain.The results of numerical calculations show that when the impurity is located at the core boundary,the impurity binding energy decreases first and then increases with the increase of the core radii,and decreases monotonically with the increase of the shell radii;when the impurity is located at the center and boundary of the shell,the impurity binding energy increases monotonically with the increase of the core radii,and decreases monotonically with the increase of the shell radii;the peak intensity of photoionization cross section increases with increasing core radii at different impurity positions,and meanwhile the peak position appears red or blue shift.In addition,the strain effect has a significant influence on the binding energy and photoionization cross section,and the influence obviously depends on the impurity position.Secondly,the relationship between the impurity binding energy in CdTe/Cd1-xZnxS/CdTe multi-shell spherical quantum dots with the size of quantum dots and Zn composition is studied.Through calculation,it is found that when the impurity is located at the center of the quantum dot,the electron may be localized in the core or outer shell region with the change of the quantum dot size,which has a significant influence on the impurity binding energy.When electrons are localized in different regions,the change of the impurity binding energy with Zn component is closely related to impurity position.Finally,the exciton binding energy,radiation lifetime and pressure effects in type Ⅰ and Ⅱ structures of CdTe/Cd1-xZnxS strained core-shell spherical quantum dots have been studied.The results show that for both structures,the exciton binding energies with and without strain decrease with the increase of core radii but increase with the increase of pressure.The exciton binding energy with strain is smaller than that without strain.The effects of shell radius and strain on the exciton binding energy are obvious in the type Ⅱ structure,and the radiation lifetime increases first and then decreases with the increase of pressure.For type Ⅰ structure,the effect of strain is relatively small,and the radiation lifetime decreases monotonically with the increase of pressure.