Excitonic States In Asymmetrically Coupled Double Quantum Wells Of GaAs/Al_xGa_1-xAs

A variational method is adopted to investigate the binding energies of excitons in asymmetrically coupled double quantum wells (ACDQWs) of GaAs/AlxGa1-xAs by considering the effects of the ternary mixed crystal, size and pressure.Firstly, some basic physical properties of semiconductor quantum wells have been briefly reviewed in this thesis, the research progress in symmetrically coupled double quantum wells (SCDQWs) especially the achievements of relative excitonic states is focused. Furthermore, the experimental and theoretical studies and shortcoming of excitonic states in ACDQWs are also introduced briefly.In this thesis, a detailed calculation about the variation relations of the binding energy of excitons in ACDQWs changing with the left well width and middle barrier thickness is given and the influences from Al component and pressure are also discussed. The average positions of an electron and a hole in the z direction in ACDQWs as a function of left well width and middle barrier width are given. Furthermore, our results are compared with that of SCDQWs. The numerical results indicate that the binding energies of ACDQWs exhibit significantly different properties from that of SCDQWs due to the coupling effect of the double wells. The binding energies decrease firstly to a minimum then increase and finally decrease with increasing the left well width when the middle barrier thickness takes a smaller fixed value; on the other hand, as the barrier width increase, the binding energies show a slight oscillation at first, then suddenly decrease. The influence from Al component and pressure obviously depends on the coupling effect and the symmetry of double wells.