Optical Absorption Of Electron Intersubband Transition In Double Parabolic Quantum Wells Of GaAs/AlGaAs

Some realizable structures of double parabolic quantum wells?DPQWs?consisting of Al_xGa_1-xAs/Al_yGa_1-yAs are constructed.Mainly focused on the asymmetric cases for the above structures,the electronic states are obtained using a finite difference method to solve the Schr?dinger equation.Furthermore,based on a density matrix approach,the optical absorption coefficients?OACs?and refractive index changes?RICs?induced by intersubband transition of electrons in these three energy level systems at room temperature are discussed.The effects of size and ternary mixed crystal are investigated.The results of symmetric and asymmetric cases are compared with that of double square quantum wells?DSQWs?.Firstly,the development of relative semiconductor quantum wells are briefly introduced,and the research history and current situation about optical absorption and refractive index due to the optical absorption of electrons intersubband transition in coupled double quantum wells are mainly explained.The theoretical results and existing defects in the relative problems are described in detail.It is pointed out that the DPQWs structure can importantly modulate the optical absorption and refractive index.Furthermore,the influence of well widths,middle barrier thicknesses,Al component,incident light intensity,relaxation time and external electric fields on optical absorption and RIC of electrons intersubband transition are discussed theoretically in detail.The results reveal that the peak position and height of intersubband OACs and RICs in DPQWs are sensitive to the barrier height modulated by the Al component.What's more,external electric fields result in the decrease of peaks,and play an important role in the blue shift of absorption spectra due to electrons excited from ground state to first and second excited states.Our results show that the line absorption coefficient from ground to the second state transition is comparatively small and can be increased by decreasing middle barrier thicknesses and applying an external electric field F?28?15 k V/cm in an asymmetric structure in order to embody the couple of double wells.In addition,the value of the incident light intensity can affect the peak of the total OACs and the RICs,when the incident light intensity is very strong,the single peak of total absorption coefficient splits into two peaks,leading to a bleaching effect.The value of relaxation time can affect the half width of absorption peaks.With the increase of relaxation time,the half width of an absorption peak decreases.By comparison,it is found that the peaks of intersubband OACs and RICs are smaller in asymmetric DPQWs than that in symmetric ones.The results also indicate that the adjustable extent of incident photon energies for DPQWs is larger than that for square ones in the similar size.Our results are helpful for improving the opto-electronic properties and giving theoretical guidance for device fabrication.