TUNNELING AND TRANSPORT VIA LOCALIZED STATES IN THIN AMORPHOUS SILICON TUNNEL BARRIERS AND THE APPLICATION OF THESE BARRIERS IN A TUNNELING STUDY OF SUPERCONDUCTING VANADIUM-GALLIUM ALLOY FILMS (RESONANT, APB APPROXIMATION, HOPPING, INELASTIC)

Part I. The goal of Part I of this thesis is to gain an understanding of "real" potential tunnel barriers in metal/insulator/metal tunnel junctions beyond the conventional 'average potential barrier' approximation which is used to describe them. In particular we hope to understand the role of localized states in the tunnel barrier and their contribution to the conductance of the junction.; To investigate this we have generated systems based on composite amorphous silicon/silicon oxide barriers. By careful manipulation of the symmetry of such structures situations were created where transport was dominated either by classic "direct" tunneling or by resonant tunneling via localized states in the a-Si. Those junctions which were dominated by resonant tunneling were then studied comprehensively as a function of temperature and junction bias voltage. Furthermore, resonant tunneling via individual localized states was resolved in a series of sub-micron dimension tunnel junctions.; In general we find that localized states in all "real" tunnel barriers can contribute considerably to the tunneling conductance, and can strongly influence the form of the current-voltage characteristic observed.; Part II. The goal of Part II of this thesis is to gain an understanding of superconductivity in the high critical temperature superconductor vanadium-gallium.; Tunnel junctions were made on thin films of the material and then examined as a function of vanadium-gallium alloy composition under various conditions. Conclusions were then drawn about the mechanism of superconductivity in this system.