Nanoscale Schottky contact surface plasmon "point detectors" for optical beam scanning applications.

Abstract

We propose and investigate a Schottky contact detector where the contact metal is a nanoscale metal stripe waveguide supporting surface plasmons with strong localization along the Schottky contact. We consider Au for the metal stripe, p-doped silicon for the semiconductor, operation in the infrared (at λ0=1550 nm), and internal photoemission as the sub-bandgap detection mechanism. We find that the main surface plasmon mode of operation of the Au stripe exhibits diverging real and imaginary parts of neff with decreasing stripe dimensions, commensurate with increasing confinement. The mode fields are tightly confined to the immediate vicinity of the stripe within a very small area. Coupling efficiencies, responsivities, dark currents, and minimum detectable powers are computed. An application envisaged for such nanoscale "point detectors" is optical beam scanning, motivated by the very small area of the photodetector stripe mode relative to, e.g., a Gaussian beam (∼500× smaller), such that its field distribution approximates a Dirac delta function in comparison, and by the photocurrent originating primarily from selective absorption of the photodetector stripe mode. The proposed application was verified through numerical simulation, demonstrating that a nanoscale "point detector" can scan a tightly focused Gaussian beam (2.5 μm diameter at λ0=1550 nm) with good resolution and signal to noise.