Solar spectrum rectification using nano-antennas and tunneling diodes

Our goal is to develop a rectifying antenna (rectenna) applicable to solar spectrum energy harvesting. In particular, we aim to demonstrate viable techniques for converting portion of the solar spectrum not efficiently converted to electric power by current photovoltaic approaches. Novel design guidelines are suggested for rectifying antenna coupled tunneling diodes. We propose a new geometric field enhancement scheme in antenna coupled tunneling diodes that uses surface plasmon resonances. For this purpose, we have successfully implemented a planar tunneling diode with polysilion/SiO2/polysilcon structure. An antenna coupled asymmetric tunneling diode is developed with a pointed triangle electrode for geometric field enhancement. The geometrically asymmetric tunneling diode shows a unique asymmetric tunneling current versus voltage characteristic. Through comparison with crossover tunneling diodes, we verified that the current asymmetry is not from the work function difference between the two electrodes. Results of RF rectification tests using the asymmetric diode demonstrate that our approach is practical for energy harvesting application. Furthermore, we describe how surface plasmons can enhance the electric field across the tunnel junction, lowering the effective "turn-on" voltage of the diode, further improving rectification efficiency.