Opptical Absorption Via Intersunband Transition Of Electrons In GaAs/AlGaAs Multi-quantum-Wells In An Electric Field

Multi-quantum wells?MQWs?are widely used in infrared laser detection devices because of the favorable optical absorption properties of electronic transition.GaAs which constitutes the long-wavelength MQW structures not only have the advantage of high electron transport properties and high mobility same as III-V semiconductors,but also is possible to prepare Ga As/Al_xGa_1-xAs heterojunctions with stable properties,and therefore becomes one of the preferred materials for MQWs.In recent years,the studies on the effects of size and ternary mixed crystal?TMC?on electron intersubband optical absorption in MQWs have been accumulated more.However,the work on the modulation of the above properties by an applied electric field is still insufficient.Firstly,based on the effective mass approximation,by consideration of the effect of the lateral electric field?LEF?on MQWs,the Schr?dinger equation and Poisson equation of electrons in conduction band are self-consistently solved by the finite element difference method to obtain the ground state,first excited energy levels and the corresponding wave functions.Furthermore,the third-order nonlinear intersubband optical absorptions coefficients?IOACs?and refractive index changes?RICs?are solved by the density matrix method.Secondly,the effects of size,TMC effect,doping concentration N_D,temperature T and incident light intensity I on IOACs and RICs are discussed based on the Fermi's golden rule.The result shows that,under a fixed LEF,the peak positions of IOACs appear red shifts with increase of Al composition x or N_D,blue shifts with increase of well or barrier widths,whereas,blue shifts appear first and then red shifts do with increasing T.It also can be found that,the photobleaching phenomenon becomes more pronounced because the third order nonlinear IOACs increase rapidly with increase of I and well or barrier widths.When the above parameters are given,the peak positions of IOACs appear blue shifts with increase of LEF.The RICs also have similar properties,for example,they can be reduced by increasing I or decreasing the well or barrier widths.Finally,the IOACs of 2 MQW structures are calculated and our theoretical results are compared with that of experiments.