Optical Absorption Properties Of Wurtzite GaN/In_xGa_1-xN/GaN Spherical Core-shell Quantum Dots

Using a finite difference method and density matrix principle,we have studied the optical absorption properties of the intersubband and interband in a wurtzite GaN/In_xGa_1-xN/GaN spherical core-shell quantum dot?CSQD?with built-in electric field?BEF?.We have investigated the influences of BEF and incident optical intensity,and discussed the size and ternary mixed crystal?TMC?effects on optical absorption coefficients?OACs?and refractive index changes?RICs?.The main results obtained are as following:The optical absorption properties of the intersubband have been investigated.The results show that the transition energy is greatly reduced due to the decrease of electron energy level difference,and the peak positions of OACs and RICs present a red shift when the BEF is taken into account;It is also found that the OACs and RICs are saturated with the increase of incident light intensity.As the same time,the peaks of OACs are split and the secondary peaks appear near the zero values of RICs;When the component x increased,the peak positions of OACs and RICs shift to higher energy,and the peak intensities of OACs decrease dramatically.However,the peak intensities of RICs have a small dependence on composition x;Our results also reveal that the peak positions of OACs and RICs show a red shift,and the peak intensities of RICs increase significantly with the increase of core radius and well width.The peak intensities of OACs have a small dependence on well width,and decrease with the increase of core radius.We have studied the optical absorption properties of the interband.The results indicate that when the strong BEF is considered,the coupling effects between the electron and hole wave functions are weakened,and the peak intensities of OACs and RICs have a remarkable reduction about one order of magnitude,and the peak positions of OACs and RICs have a distinct blue shift;It is also found that the OACs and RICs are saturated with the increase of incident light intensity;The peak intensities of OACs and RICs shift to the lower energy,and the peak intensities reduce dramatically with the increase of composition x.Size effects indicate that both the increase of core radius and the decrease of well width lead to a blue shift of the OACs and RICs.The peak intensities of OACs and RICs have a small dependence on core radius,but decrease with the increase of well width.By comparison,the effect of BEF on the interband optical absorption property is more significant.Furthmore,the interband optical absorption present a higher OAC,and the higher order nonlinear absorption process is more easily observed in the intersubband optical absorption.These results are expected to be helpful for the design of CSQD structure devices.