Abstract

We have developed a new ultrafast graphene diode and demonstrated its operation at 28 THz. This diode relies on geometric asymmetry and the long charge mean-free path length in graphene to provide asymmetric electrical characteristics. Fabricated geometric diodes exhibit asymmetric direct current (DC)–voltage characteristics, which agree well with Monte Carlo simulations based on the Drude model. Since an applied gate voltage can control the charge carrier type (electrons or holes) and concentration, the polarity of the diode can be reversed. The planar structure of the geometric diode provides the low resistor capacitor (RC) time constant, on the order of 10⁻¹⁵ s, necessary for operation at optical frequencies. When coupled to an antenna, the diode induces rectification of high-frequency optical signals. We formed rectennas by coupling geometric diodes with bowtie antennas and verified optical rectification at 28 THz, using both metal and graphene antennas. Applications of geometric diodes coupled to bowtie antennas include detection of terahertz and optical waves, ultra-high-speed electronics, and optical power conversion.