Exciton And Impurity State In Semiconductor Quantum Wells In An Electric Field

The corresponding problems of excitons and impurity state in quantum well structures subjected to an external electric field are investigated. In our investigation, the electron (hole) and optical phonon modes interaction in quantum wells have been studied.Firstly, within the framework of the effective mass approximation, a variational method is used to calculate the binding energies and corresponding Stark shifts of excitons in quantum well structures in a weak electric field by taking the exciton-LO phonon field coupling into account by using an effective potential derived by A. Antonelli et al The binding energies and corresponding Stark shifts for III- V and II-VI compound semiconductor quantum well structures have been numerically computed. The results for GaAs/Al_xGa_1-xAs and Zn_1-xCd_xSe/ZnSe quantum wells are given and discussed. Theoretical results show that the exciton-phonon coupling reduces both the exciton binding energies and the Stark shifts by screening the Coulomb interaction. This effect depends on both the well-width and the polarity of the materials. This effect is observable experimentally and cannot be neglected for wider wells, particularly in II -VI compound systems.Then, the binding energies and corresponding Stark shifts of impurity state in quantum wells are investigated with a variational method by considering the influence of infinite barriers in an external electric field. In the calculation, we take the impurity state with longitudinal optical (LO) phonon and interface optical (IO) phonon interaction into account. The binding energies are obtained as functions of the well width, the impurity position and the electric field strength. The results for GaAs/Al_0.3Ga_0.7As quantum wells are given and discussed. The numerical results show that the donor impurity binding energies increase monotonically with decreasing well width when...