Light emission from microstructured tunnel junctions

Metal-insulator-metal tunnel junctions of aluminum-aluminum oxide-gold are fabricated with silver particulates positioned above the gold electrode by means of a magnesium fluoride spacer. The particulates are formed on the spacer by annealing a thin film of silver. Light emission is observed from these junctions when a bias voltage is applied across the oxide. Data are presented showing emitted light intensity as a function of wavelength, polarization, and angle of emission. A simple model is described in which tunneling current fluctuations are characterized by a single uniformly moving electron which stimulates surface plasmons in the gold electrode. The surface plasmon field is obtained and its effects on microparticulates are described as driving surface plasmon modes in these microparticulates. While all aspects of the theory are not completely matched to the experimental conditions, the results are a new basis for qualitatively understanding the junction spectra.