Effects Of Potential Barriers On Binding Energies Of Impurity States In GaAs/Al_xGa_1-xAs Quantum Wells And The Influence From Magnetic Fields

Within the framework of effective mass approximation, the effects of potential barriers on binding energies of impurity states in GaAs/AlxGa1-xAs quantum wells and the influence from magnetic fields have been investigated theoretically. There are two parts in this thesis.In the first part, the research development and history on the impurity states in quantum wells and related low dimensional materials of semiconductor are reviewed. The motivation of the present work is clarified.In the second part, a variational method is used to investigate the effect of barriers on binding energies of impurity states in GaAs/AlxGa1-xAs quantum wells and the influence from a magnetic field perpendicular to the interfaces. The relations between binding energies and well widths, barrier thickness, impurity positions, magnetic fields are given, respectively. Furthermore, their pressure effect is discussed. A comparison with that of quantum wells with infinitely high barriers and infinitely thick barriers is given. The results indicate that the binding energy for a quantum well with finitely high barriers is obviously less than that with infinitely high barriers, whereas the binding energy for a quantum well with finitely thick barriers is bigger than that with infinitely thick barriers for a small well width. The difference among the three cases becomes small as the well width increases. The binding energies are influenced strongly by the confinement of a magnetic field, and increase as the strength of a magnetic field increases. The binding energies influenced by magnetic fields increase monotonically as increasing pressure. The modification on the barriers in the thesis should be considered in future works.