Theoretical study of tunneling phenomena in heterostructures and theory of pair impurities in semiconductors

A formalism is developed for computing the charge-state splittings of deep levels associated with paired defects and is applied to nearest-neighbor substitutional sulfur pairs in silicon. Self-consistent calculations predict a 0.19 eV splitting between the deep levels of nearest-neighbor (S,S){dollar}sp{lcub}rm o{rcub}{dollar} and (S,S){dollar}sp+{dollar} in Si, in good agreement with the experimental value of 0.18 eV. Computed ratios of hyperfine tensor components also agree with available data. Our results lend support to the meso-bonding model of paired-chalcogen deep levels.; We have studied the influence of a quantum size tunnel barrier and tunnel barrier structure on the tunneling current in metal/semiconductor(insulator)/metal junctions using the non-equilibrium Green's function technique and the tunneling current formalism of Caroli et al. in a tight-binding basis. The quantization effects of the ultra-thin film barrier are studied, and the effect of the applied potential difference on the band edges and distribution function of the thin semi-conducting layer is obtained. Interband Zener tunneling is also found for high voltages, or small band gaps in the semiconductor. In addition to obtaining the exact non-equilibrium Green's function in the barrier, we also consider ultra-thin semiconductor barrier layers, for which the transfer Hamiltonian approximation to the tunneling current breaks down, and study the influence of interfacial metal/semiconductor overlap integrals on the current.; The resonant tunneling phenomenon through quantum-well states in a one-dimensional double-barrier single quantum-well heterostructure is studied using the nonequilibrium tunneling theory of Caroli et al. and scattering theoretic Green's function technique with a simple model Hamiltonian. The effect of external bias is found exactly in the calculation of Green's function for the junction within this model, obviating any restriction on the magnitude of the external bias. The density of states of the junction, its dependence on the external bias, and the formation of bound states in the quantum-well region are discussed. Our results for the tunneling current yield resonance peak to valley ratios in reasonably good agreement with experiment, indicating that this treatment of the tunnel junction when applied to real materials can more accurately describe existing experimental results. (Abstract shortened with permission of author.)...