Interface Impurity States And Bound Polarons In Realistic Semiconductor Heterojuntion Potential Under Magnetic Fields And The Pressure Effects

In this thesis, when a magnetic field exists, the donor impurity states and polarons near the interfaces in semiconductor heteroj unctions are investigated with a realistic heteroj unction potential model including the influences of finite potential barrier and energy band bending. Meanwhile, the pressure effect is also discussed.First, a variational method is adopted to investigate the ground state of an electron bound to a donor impurity near a single semiconductor heteroj unction. The relations between the ground state binding energy and the magnetic field strength, the Al concentration, the areal electron density and the impurity position are given respectively. The numerical results for GaAs/AL.Ga1-xAs heteroj unctions show that the impurity state binding energy increases obviously as the increase of the magnetic field strength.Furthermore, considering the longitudinal optical (LO) phonons and two branches of interface optical (10) phonons, an improved Lee-Low-Pines (LLP) transformation is used to deal with the electron-phonon and impurity-phonon interactions. The binding energies of bound polarons as functions of pressure, magnetic field and impurity position are obtained by a variational method. In the calculation, the pressure effects of the phonon frequency, band offsets between channel and barrier materials, the electron effective mass and the dielectric constant are considered.For GaAs/AlxGa1-xAs heteroj unctions, the results show that the phonon contribution to the binding energy is negative and both the LO phonon and IO phonon give important contribution to the binding energy. The binding energy and the contribution from phonons to the binding energy increase with pressure (0.0kbar-40.0kbar) and magnetic field (0.0T-70.0T) increasing. As the impurity position varying from the interface to channel side, the binding energy increases to a maximum and then decreases gradually. The contribution from the IO phonons to the binding energy changes non-obviously then decreases gradually and that of the LO phonons increases obviously to a maximum then decreases as the distance between the impurity and the interface increases. The influence of magnetic field on the contribution of the IO phonons is nearly linear increase and the influence on the contribution of the LO phonons is nonlinear increase whereas the influences of pressure on the both are linear increase. The magnetic and pressure effects on the LO phonons are more obviously.