Observation and explanation of light-emission spectra from statistically rough Cu, Ag, and Au tunnel junctions

Abstract

A detailed description of the experimentally observed light output from statistically rough ${\mathrm{A}\mathrm{l}\ensuremath{-}\mathrm{A}\mathrm{l}}_{2}$${\mathrm{O}}_{3}$-$M$ ($M=\mathrm{A}\mathrm{g},\mathrm{A}\mathrm{u},\mathrm{C}\mathrm{u}$) tunnel junctions is presented. These data include a comprehensive description of the polarization and angular distribution of the light emitted from ${\mathrm{A}\mathrm{l}\ensuremath{-}\mathrm{A}\mathrm{l}}_{2}$${\mathrm{O}}_{3}$-Au junctions as well as spectra from reverse-biased ${\mathrm{A}\mathrm{l}\ensuremath{-}\mathrm{A}\mathrm{l}}_{2}$${\mathrm{O}}_{3}$-Ag junctions. It is argued, principally on the grounds of an examination of surface-plasmon---polariton (SPP) damping, that the bulk of the output from statistically rough tunnel junctions is due to the fast-SPP mode. The idea of fast-SPP mediation is found, in many respects, to be much more consistent with currently available experimental results than that of slow- (or junction) SPP mediation. Extant theoretical models hold slow-SPP mediation to be the dominant means of visible-regime emission. The view of the emission mechanism presented in this paper suggests that the statistically rough tunnel junction could emit light more efficiently (if the scale of the surface roughness were altered) and that it has potential as a spectroscopic tool.