Classical and quantum responsivities of geometrically asymmetric metal-vacuum-metal junctions used for the rectification of infrared and optical radiations

The authors study the rectification properties of geometrically asymmetric metal-vacuum-metal junctions in which a combination of static and oscillating biases is established between a cathode that is extended by a hemispherical protrusion and a flat anode. The static current-voltage characteristics of this device are established using a transfer-matrix methodology. The rectification properties of the device are, however, analyzed in the framework of a classical model that is based on the Taylor-expansion of static current-voltage data. This enables the impedance and the classical responsivity of the device to be established. The authors then investigate how the impedance and the classical responsivity of this junction are affected by the work function of the materials, the gap spacing between the cathode and the anode, and the aspect ratio of the protrusion. They also consider the efficiency with which the energy of incident radiations can be converted using this device. The authors finally compare the responsivity obtained using this classical approach with the quantum responsivity one can define from the currents actually achieved in an oscillating barrier. This work provides additional insight for the development of a device that could be used for the energy conversion of infrared and optical radiations.