Surface Plasmon-Polariton Schottky Photodetectors

Abstract

This article thesis presents the full design, fabrication, characterization and testing of two surface plasmon-polaritons (SPPs) photodetectors operating at telecommunication wavelengths.Surface plasmon photodetectors are of great current interest. Such detectors typically combine a metallic structure that supports surface plasmons with a photodetection structure based on internal photoemission or electron-hole pair creation. We present two metal nano-structures supporting SPPs, integrated into a silicon-based Schottky-contact photodetector: an array of nanoantennas and nano-gratings. In both structures, incident photons coupled to the array excite SPPs on the gold (Au) nanowires of the antennas which decay by creating "hot" carriers in the metal. The hot carriers may then be injected over the potential barrier at the Au-Si interface resulting in a photocurrent.A metal grating is used to couple perpendicularly-incident light to SPPs propagating along a thin metal patch forming a Schottky contact to p-Si. The responsivity is enhanced by the absorption of SPPs directly along the Schottky contact leading to the creation of hot holes near the contact. Our measurements reveal a high responsivity of ~13 mA/W at telecom wavelengths (~1550 nm) and under low reverse bias. The responsivity increases with reverse bias. The optical bandwidth (FWHM) is ~80 nm. These detectors have many important advantages such as speed, simplicity, compatibility with silicon, and low-cost fabrication.In the nanoantenna case, high responsivities of 100 mA/W and practical minimum detectable powers of −12 dBm should be achievable near 1550 nm which makes monitoring of the spectral response very easy. The device was then investigated for use as a biosensor by computing its bulk and surface sensitivities. Sensitivities of ∼250 nm/RIU (bulk) and ∼8 nm/nm (surface) in water are predicted. We identify the mode propagating and resonating along the nanowires of the iii antennas, we apply a transmission line model to describe the performance of the antennas, and we extract two useful formulas to predict their bulk and surface sensitivities. As a biosensor, this structure offers significant advantages as it simplifies the interrogation setup: only the photocurrent generated by the device needs to be monitored, and the excitation optics (bottom) is physically separated from the micro-fluidics (top) by the device. We also propose a Schottky contact photodetector based on electrically-contacted Au nanoantennas on p-Si for the plasmonic detection of sub-bandgap photons in the optical communications wavelength range. This highly compact component is very promising for applications in high-density Si photonic integration.iv