Optical Properties Of Hydrogenic Impurity States In A Wurtzite In_xGa_1-xN/GaN Core-shell Quantum Dot

Due to the strong built-in electric field（BEF）in wurtzite materials,the ground and excited energy state energies and wave functions have been calculated by finite difference method with the impurity and the BEF.Moreover,we have investigated the intersubband optical property of the hydrogenic impurity states in a wurtzite In_xGa_1-xN/GaN core-shell quantum dot（CSQD）using density matrix principle.We have studied the influences of impurity and BEF,and discussed the ternary mixed crystal（TMC）effects,QD size,incident optical intensity and relaxation time on optical absorption coefficients（ACs）and refractive index changes（RICs）.The following results can be obtained through analysis:When the presence of impurity,the transition energy is obviously increased,and the linear,nonlinear and total ACs and RICs resonant peaks for all transitions move towards the higher photon energies.With increasing In-composition x leads to an distinct blue shift of the resonant peaks for 1s-1p,1p-1d and 1d-1f transitions.At the same time the amplitudes of the total ACs increase with the increment of x,while for the total RICs the amplitudes decrease.It is also found that the resonant peaks of ACs and RICs show a red shift,and the peak amplitudes of third-order nonlinear ACs and RICs increase dramatically with the increment of core radius.However,the peak amplitudes of first-order linear ACs have a small dependence on core radius.Therefore,the total ACs decreases as the core radius increases.In addition,the resonant peaks of total ACs are split and the secondary peaks appear near the zero values of total RICs,which because the saturation of the ACs and RICs caused by the incident optical intensity I and relaxation timeτexceed a threshold value.Moreover,the appearance of absorption saturation require a larger incident optical intensity when considering the impurity.When the presence of BEF,the transition energy is obviously increased,and the linear,nonlinear and total ACs and RICs resonant peaks for all transitions have a significant blue shift.When increasing In-composition x,the resonant peaks for all transitions move towards the higher photon energies with the impurity and the BEF.Moreover,it is also found that the amplitudes of the total ACs increase with the increment of x,while for the total RICs the amplitudes decrease.In addition,the resonant peaks of ACs and RICs move towards the lower photon energies,and the peak amplitudes of linear and nonlinear ACs and RICs increase significantly as the core radius increases.Meanwhile,the total ACs decreases and the total RICs increases with increasing core radius.Moreover,the resonant peaks of total ACs are split and the secondary peaks appear near the zero values of total RICs,which because the saturation of the ACs and RICs caused by the incident optical intensity I and relaxation timeτexceed a threshold value.And the appearance of absorption saturation require a larger incident optical intensity when considering the BEF.