Quantum Tunnelling in Heterostructures.
Available from UMI in association with The British Library. This thesis presents the results of a microscopic calculation of the electron tunnelling properties in finite semiconductor heterostructure systems. Empirical pseudopotentials are used to incorporate the microscopic crystal potential and a scattering matrix method is developed to solve the electron wave function through the system. The effects of the inherent bandstructure on the tunnelling characteristics are examined in some detail. Non-parabolicity in the Gamma state bandstructure in the bandgap region alone is found to produce significant deviations in the tunnelling current and resonant energies from the simplistic effective mass approximation. Many-band effects are found to be important for indirect bandgap barriers where the electron energy lies above the barriers' X minima. The situation in the purely tunnelling regime is dominated by the Gamma state, regardless of the nature of the bandgap. Finite electric fields in large systems are considered. Gamma-X real space intervalley transfers are found when the electron energy traverses the conduction band edge of a material. The total wave function is in general complicated due to the highly complex mixing of the different states' contributions. The effects of the bandstructure changes on the tunnelling properties in single and multiple barrier systems due to the application of hydrostatic pressure are also examined. The results show that in single barriers the direct to indirect bandgap transition alone does not modify significantly the tunnelling property but deviations from the single -band behaviour are found when the conduction band edge is lowered below the electron energy. In multiple barrier systems the lowering of the barrier's X minima effectively pushes up the Gamma resonant level in wells such that a clear negative differential resistance signal would be lost.
- Pub Date:
- Physics: Electricity and Magnetism