We demonstrate a new thin-film graphene diode called a geometric diode that relies on geometric asymmetry to provide rectification at 28 THz. The geometric diode is coupled to an optical antenna to form a rectenna that rectifies incoming radiation. This is the first reported graphene-based antenna-coupled diode working at 28 THz, and potentially at optical frequencies. The planar structure of the geometric diode provides a low RC time constant, on the order of 10 −15 s, required for operation at optical frequencies, and a low impedance for efficient power transfer from the antenna. Fabricated geometric diodes show asymmetric current-voltage characteristics consistent with Monte Carlo simulations for the devices. Rectennas employing the geometric diode coupled to metal and graphene antennas rectify 10.6 µm radiation, corresponding to an operating frequency of 28 THz. The graphene bowtie antenna is the first demonstrated functional antenna made using graphene. Its response indicates that graphene is a suitable terahertz resonator material. Applications for this terahertz diode include terahertz-wave and optical detection, ultra-high-speed electronics and optical power conversion.

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Optical rectennas, consisting of micron-size antennas coupled to high speed diodes, operate by collecting electromagnetic radiation and converting the high frequency AC field to DC power. We report the demonstration of optical rectennas operating at a wavelength of 10.6 µm. The diode is a graphene device that relies on geometric asymmetry to provide rectification. It is coupled to a metal bowtie antenna 5.1 µm in length. The planar configuration of the diode gives it an extremely low capacitance, making it more suitable for high frequency operation than metal-insulator-metal (MIM) diodes. The theoretical efficiency limit of such devices exceeds the Shockley-Queisser limit, making them suitable for broadband optical operation, and in specific, for thermophotovoltaics.