Intraband Transition Optical Absorption Of Electron In Parabolic Potential InGaN/GaN Core Shell Quantum Dot

Based on the density matrix approach,the intraband transition optical absorption has been investigated in parabolic potential InGaN/GaN core shell quantum dot(CSQD)and GaN/InGaN inverted core shell quantum dot(ICSQD)with and without impurity.The finite difference method was employed in the calculations.The effects of size and ternary mixed crystal are discussed in detail.The results of the two QD structures are compared.The results of intraband transition optical absorption in a InGaN/GaN CSQD are as follows:As the core radius increases,all absorption peaks of the optical absorption coefficients(OACs)exhibit an obvious blue shift and then red shift,the amplitudes of the OACs increase first and then decrease,while the total refractive index changes(RICs)decrease first and then increase.When considering the impurity,the blue shift(red shift)increases obviously,and the impurity also has a significant influence on the amplitudes of the total OACs and RICs.With increasing shell thickness or decreasing In-composition,all absorption peaks of the OACs present a red shift,the amplitudes of the total OACs decrease and the total RICs increase.When considering the impurity,the dependence of absorption spectrum on the shell thickness(composition)decreases(increases),that is,the red shift decreases(increases)significantly.Meanwhile,the amplitudes of the total OACs increase,and the amplitudes of the total RICs decrease.All amplitudes of the total OACs increase with decreasing the incident optical intensity and increasing the relaxation time.When the incident optical intensity or relaxation time is large enough,absorption saturation occurs,and the total absorption peaks split into two peaks,and the absorption saturation requires larger incident optical intensity and relaxation time in the presence of impurity.The results of intraband transition optical absorption in a GaN/InGaN ICSQD are as follows:As the core radius or shell thickness increases,all absorption peaks of the OACs suffer a red shift.It is also found that the amplitudes of the total OACs decrease and the total RICs increase.In addition,the red shift is more noticeable with impurity,as well as impurity effect on the amplitudes of the total OACs and the total RICs is significant.In contrast,increasing In-composition leads to a blue shift of all absorption peaks of the OACs,the amplitudes of the linear,nonlinear,total OACs and RICs increase.When impurity is considered,the blue shift increases significantly,the amplitudes of the total OACs decrease and the total RICs increase.The amplitudes of the total OACs have a strong dependence on the incident optical intensity and relaxation time,when they exceed their critical value respectively,a collapse at the center of the peak is observed.And it is found that the impurity has little influence on the results.Comparing the calculation results of the two QD structures,we found that InGaN/GaN CSQD can absorb the photons with higher frequency than GaN/InGaN ICSQD,while the ICSQD is more sensitive to the incident optical intensity and relaxation time.In addition,when considering the impurity,the absorption spectra of both the two structures all move toward higher energy,and the absorption spectrum range of InGaN/GaN CSQD is significantly broaden,while the influence on the GaN/InGaN ICSQD is relatively small.The results are helpful to provide theoretical guidance for experimental design and device fabrication of GaN-based quantum dots.