Yagi-Uda nanolithographic antennas on a Si photodiode for infrared detection*

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 based on a direct electrical measurement obviating the need for an ITO coating or back contact. The measurements demonstrate control of directivity and wavelength selectivity in an array of 400 nanoantennas. With incident 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, respectively, in agreement with plasmonic theory. Estimated quantum efficiencies are 5.1% and 3.1% at 1110 nm and 1690 nm, respectively, representing a fourfold increase over a device lacking the antenna array. The spatial dependence of the contribution of individual antennas in the array has been investigated to determine the process whereby resonant plasmons contribute to the photocurrent. Associated finite element modeling results will be discussed, aimed at predicting resonances in plasmonic structures with similar geometries.

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