Observation of radiative surface plasmons in metal-oxide-metal tunnel junctions

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Abstract
A peak in the ultraviolet (UV) region of the spectrum of light emitted from metal-oxide-metal (MOM) tunnel junctions has been observed at room temperature. Both the amplitude and wavelength of the peak are sensitive to applied junction bias. The UV peak corresponds to the normal or radiative surface plasmon mode while a visible peak, also present in our spectra and reported in past MOM literature, is due to the tangential or nonradiative mode. The radiative mode requires no surface roughness or gratings for photon coupling. The results show that it is possible to obtain radiative surface plasmon production followed by a direct decay into photons with MOM tunnel diodes. A MOM diode with a double anode structure is found to emit light associated only with the nonradiative mode. The thickness dependence of the UV peak along with the experimental results of the double anode MOM diode and the ratio of the UV peak to visible peak support our contention that the UV light emission is indeed due to the radiative surface plasmon.