The role of defects in the electrical properties of NbO$_{\mathrm{\mathbf{2}}}$\textbf{ thin film vertical devices}*

Epitaxial NbO$_{\mathrm{2}}$ thin films were grown on Si:GaN layers deposited on Al$_{\mathrm{2}}$O$_{\mathrm{3}}$ substrates using pulsed laser deposition. Pulsed current-voltage (IV) curves and self-sustained current oscillations were measured across a 31 nm NbO$_{\mathrm{2}}$ film and compared with a similar device made from polycrystalline NbO$_{\mathrm{2}}$ film grown on TiN-coated SiO$_{\mathrm{2}}$/Si substrate. Crystal quality of the as grown films was determined from x-ray diffractometric, x-ray photoelectron spectroscopy and atomic force microscopy data. The epitaxial film device was found to be more stable than the defect-rich polycrystalline sample in terms of current switching and oscillation behaviors.