Yagi-Uda nanolithographic antennas on a metal-semiconductor-metal photodiode*

Nanoscale Yagi-Uda antennas were fabricated on a metal-semiconductor-metal rectifying photodetector to enhance detector efficiency. A new approach for characterizing the nanolithographic optical antennas was developed and evaluated, using a direct electrical measurement obviating the need for an ITO coating or back contact. The approach was used to demonstrate control of directivity and wavelength selectivity in an array of 400 of the nanoantennas. A modified spectrometer allowed the sample to be illuminated with monochromatic light of varied angle of incidence, while electrical measurements were performed using lock-in detection. With incoming light nearly aligned to the center lobe of the Yagi-Udas, resonances in measured photocurrent were observed at 1110 nm and 1690 nm. These correspond to scaled effective wavelengths of 388 nm and 776 nm resp., in close agreement with plasmonic theory. Quantum efficiencies are estimated 5.1% and 3.1% at 1110 nm and 1690 nm resp., representing a fourfold increase over a device lacking the antenna array. With incoming light at an angle away from the main and side lobes no resonances were observed 

Reference: W. Rieger et al., Appl. Phys. Lett. 113, 023102 (2018).