Characterization of Epitaxial Ag$_{2-x}$O Thin Films Grown on Sapphire

We have grown silver oxide films with a range of stoichiometry near Ag$_{2}$O by e-beam evaporation of silver in an oxygen electron cyclotron resonance (ECR) plasma. Films were deposited on r-cut sapphire substrates. A quartz crystal oscillator was used to monitor the film growth and to determine ECR oxygen flux by examining the rate of oxygen uptake on a silver film. This information was used to select the silver rate (0.1 or 1.0 {\AA}/s) and the oxygen flow rate (from 2 to 10 sccm). XRD and RHEED analysis reveals films grew with one-dimensional $<$111$>$ epitaxy, true three-dimensional $<$002$>$ epitaxy, or a mixed phase depending on the deposition conditions. XRD and XPS shows the composition varies with deposition conditions and can be a mixture of AgO and Ag$_{2}$O. UV-vis spectroscopy shows that the films have a single absorption edge between 3.1 and 3.5 eV. Optical transmission from 500 to 700 nm is between 70 and 80{\%}. Four-point van der Pauw conductivity and Hall effect measurements indicate that the Ag$_{2-x}$O films are p-type with a conductivity on the order of 3$\times $10$^{-3} \quad \Omega ^{-1}$cm$^{-1}$.