Prism-coupled light emission from tunnel junctions containing interface roughness: Experiment

We have measured the light-emission characteristics of Al--Al oxide--Au tunnel junctions that contain residual interface roughness, and compared them with the results of a theory we have just developed [Takeuchi, Watanabe, Uehara, and Ushioda, preceding paper, Phys. Rev. B (to be published)]. The tunnel junctions were formed on a glass substrate, which is attached to a coupler prism. The light-emission intensities were measured as a function of the emission angle and energy, through the prism and on the vacuum side. The theory can fit the emission-angle dependence almost exactly for a reasonable size of roughness. It can also fit the general features of the energy spectra, but some improvements are needed to achieve perfect agreement in detail. Several avenues for further refinements are suggested.