Thin Au surface plasmon waveguide Schottky detectors on p-Si

Surface plasmon sub-bandgap Schottky detectors based on an asymmetric Au stripe waveguide on p-Si are investigated theoretically and experimentally at free-space wavelengths of λ(0) = 1310 and 1550 nm. Au on p-Si produces a low Schottky barrier (0.33 eV), which improves the internal quantum efficiency. Thick and thin Au stripes are compared, with the latter increasing the hot hole emission probability relative to the former, and thus also improving the internal quantum efficiency. Two excitation schemes are considered: end facet illumination which launches surface plasmons on the detector, and top illumination which does not. Both schemes are implemented using a piezoelectric positioner that is programmed to scan the detection area in steps of 100-200 nm, thus enabling the acquisition of high-resolution photocurrent maps. The surface plasmon detectors yield a responsivity of ~1 mA W(-1), ~2× larger than the same detectors under top illumination, due to the absorption of surface plasmons. We compare the measurements with theoretical results for both excitation schemes and estimate the hot hole attenuation length in our Au stripes to be ~23 nm.