Optical Properties Of Electron Intersubband Transtions In In GaN/GaN Multilayer Core-Shell Quantum Dot

In the frame of the effective mass approximation,the linear and nonlinear optical properties of electron intersubband transitions in InGaN/GaN multilayer core-shell quantum dots(CSQD)have been studied by using the finite difference method.We have performed a detailed investigation of hydrogenic impurity,core radius,shell thickness,well width and ternary mixed crystal(TMC)effects on optical absorption coefficients(ACs)and refractive index changes(RICs).The main results obtained are as following:The effects of hydrogenic impurity on the optical properties of the intersubband transitions in InGaN/GaN multilayer CSQD.The results show that the presence of impurity causes a blue-shift on the absorption peaks of the ACs and RICs for all transitions,especially for 1s-1p transition.The size effects on the optical properties of the intersubband transitions in In_0.2Ga_0.8N/GaN/In_0.2Ga_0.8N/GaN CSQD.It is found the absorption peaks of the ACs and RICs present a red-shift with the increase of core radius or well width for all transitions,and this effect is more obvious when considering impurity.We also found that the ACs and RICs are affected only when the shell thickness is less than 1.5nm,and the absorption peaks show a blue-shift as the shell thickness increases,and this effect decreases as considering impurity.Furthermore,the peak intensities of the ACs and RICs are strongly dependent on the core radius and well width,but less dependent on the shell thickness.The TMC effects on the optical properties of the intersubband transitions in In_xGa_1-xN/GaN/In_yGa_1-yN/GaN CSQD.The results show that the increasing of In-composition x leads the absorption peaks of the ACs and RICs to be blue-shifted for 1s-1p and 1p-1d transitions with and without impurity.And the absorption peaks for 1d-1f transition show a red-shift with x increasing in the case of impurity,while a blue-shift in the case of impurity.The absorption peaks of the ACs and RICs present a blue-shift with In-composition y increasing.When the In-composition x=y increases,the absorption peaks of the ACs and RICs show a distinct blue-shift with and without impurity.We also found that the dependence of the ACs and RICs for different level transitions on In-composition is different.The ACs and RICs for 1s-1p and 1p-1d transitions are mainly depend on the In-composition x,while the ACs and RICs for1d-1f transition rely on both In-composition x and y.