Light Emission from Microstructured Tunnel Junctions

Metal-insulator-metal tunnel junctions of aluminum -aluminum oxide-gold are fabricated wtih 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 micro-particulates 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.