Light emission from randomly rough tunnel junctions

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Abstract
Randomly rough tunnel junctions are known to emit visible light when biased at voltages that correspond to optical frequencies. It has been established that surface-plasmon polaritons (SPP’s) mediate the light output, but experiments have been interpreted to identify different SPP modes as the most important to the process. Different points of view on how the SPP modes are excited have also persisted. A series of measurements on a large number of aluminum-gold junctions that identifies the so-called slow mode as the dominant mode is reported here. This conclusion is independent of the details of theories of the light-emission process. We have also calculated the electric fields and the resulting optical spectra from biased junctions. The numerical results confirm the slow mode as the dominant mode and when compared with our data imply that inelastic tunneling current fluctuations confined to the tunneling barrier are responsible for the emitted light.