Hot-electron photodetection with a plasmonic nanostripe antenna.

Planar metal-oxide-metal structures can serve as photodetectors that do not rely on the usual electron-hole pair generation in a semiconductor. Instead, absorbed light in one of the metals can produce a current of hot electrons when the incident photon energy exceeds the oxide barrier energy. Despite the desirable traits of convenient fabrication and room-temperature operation at zero bias of this type of device, the low power conversion efficiency has limited its use. Here, we demonstrate the benefits of reshaping one of the metallic contacts into a plasmonic stripe antenna. We use measurements of the voltage-dependence, spectral-dependence, stripe-width dependence, and polarization-dependence of the photocurrent to show that surface plasmon excitations can result in a favorable redistribution in the electric fields in the stripe that enhances the photocurrent. We also provide a theoretical model that quantifies the spectral photocurrent in terms of the electrical and optical properties of the junction. This model provides an accurate estimate of the bias dependence of the external quantum efficiency of different devices and shows that both the spatial and vectorial properties of the electric field distribution are important to its operation.