Nanoantenna and Tunneling Diodes for Rectification of Mid-IR Light and Energy Generation
Nanophotonics holds great potential in emerging areas related to energy. It has been recognized for some time that it is possible to excite surface plasmons on metal surfaces and metal nanostructures and concentrate light into deep-subwavelength volumes. A great amount of work has already been published on plasmonic optical antennas for imaging (i.e. near-field scanning optical microscopy), plasmon-enhanced detectors with less noise and enhanced speed, spectroscopy applications (surface-enhanced Raman scattering), plasmonic lenses going beyond the diffraction limit, and plasmonic resonators with small volumes and reasonable field enhancements (modest Q’s of 10-100) for quantum information experiments. By comparison, few papers have discussed the use of plasmonics in energy applications but the situation is changing rapidly.
In our approach, we consider light as an electromagnetic wave exciting a radiating dipole in an antenna. The antenna can be designed such that a localized surface plasmon is resonantly excited in the antenna by the incident radiation. The nanoantenna being used by us is a bowtie antenna. The incident radiation is focused to the neck of the bowtie antenna. The electric field in the gap of the antenna is strongly enhanced. In this region, we position a dielectric layer to permit resonant tunneling of the electron gathering at the apex of the antenna. Our optical nanoantenna is therefore directly coupled to a tunneling diode, a rectifying Metal-Insulator-Metal (MIM) diode. A rectifying Metal-Insulator-Semiconductor (MIS) diode can also be used. The optical nanoantenna acts as a receiver of the infrared radiation much as a normal RF TV antenna does and then couples this radiation to a rectifying diode to yield a dc output current. No such nanoantenna coupled to a tunneling diode that uses excited localized surface plasmons has yet been demonstrated. We have already demonstrated the operation of our device at 20GHz and will also be soon reporting on infrared detection at 10 m. Our approach does not require the use of a direct bandgap semiconductor and avoids the minority carrier lifetime limitations in solar cells. This work is done in collaboration with Prof. Peckerar, from the ECE Department.