Optical frequency rectification

Abstract

Submicron antenna-coupled diodes, called optical rectennas, can directly rectify solar and thermal electromagnetic radiation, and function as detectors and power harvesting devices. The physics of a diode interacting with electromagnetic radiation at optical frequencies is not fully captured in its DC characteristics. We describe the operating principle of rectenna solar cells using a quantum approach and analyze the requirements for efficient rectification. In prior work classical concepts from microwave rectenna theory have been applied to the analysis of photovoltaic power generation using these ultra-high-frequency rectifiers. Because of their high photon energy the interaction of petahertz-frequency waves with fast-responding diodes requires a semiclassical analysis. We use the theory of photon-assisted transport to derive the current-voltage [I(V)] characteristics of metal/insulator/metal (MIM) tunnel diodes under illumination. We show how power is generated in the second quadrant of the I(V) characteristic, derive solar cell parameters, and analyze the key variables that influence the performance under monochromatic radiation and to a first-order approximation. The photon-assisted transport theory leads to several conclusions regarding the high-frequency characteristics of diodes. The semiclassical diode resistance and responsivity differ from their classical values. At optical frequencies, a diode even with a moderate forward-to-reverse current asymmetry exhibits high quantum efficiency. An analysis is carried out to determine the requirements imposed by the operating frequency on the circuit parameters of rectennas. Diodes with low resistance and capacitance are required for the RC time constant of the rectenna to be smaller than the reciprocal of the operating frequency and to couple energy efficiently from the antenna. Finally, we carry out a derivation that extends the semiclassical theory to the domain of non-tunneling based diodes, showing that the presented analysis is general and not restricted to the MIM diode.