| Understanding the doping mechanisms in metal-oxide superconductors is an important part of probing the superconductor theory. Modulation of the carrier concentration using electric fields to tune superconductivity is a good method for this approach for its ability to minimize changes in both chemical impurities and structure.;This thesis explores the electric field modulation of normal state properties and superconductivity in thin-film field-effect transistors based on lanthanum-doped strontium titanate channels and undoped strontium titanate gate insulation. Electric field tuning of normal-state sheet resistance and channel critical current are observed in enhancement (positive gate potential) and depletion (negative gate potential) modes, consistent with an electric field induced variation of channel depletion width. Detailed analysis of the non-linear channel current-voltage characteristics is consistent with electric field modulation of a 2-dimensional Kosterlitz-Thouless transition and shows the scaling of TKT (Kosterlitz-Thouless transition temperature) with conduction channel thickness and normal conductance at different gate fields.;Also, small signal modulation experiments were performed on these devices. Modulation of critical current, sheet resistance, and TKT is found for frequencies out to at least 1 kHz, which indicates possible exciting superconductor electronics. |
