  We propose a polarization-insensitive and high-efficiency plasmonic silicon
Schottky diode for detection of sub-bandgap photons in the optical
communication wavelength range through internal photoemission. Our photodiode
is based on a hybrid plasmonic silicon waveguide. It has a gold film covering
both the top and the sidewalls of a dielectric silicon waveguide with the
Schottky contact formed at the gold-silicon interface. An extensive physical
model is presented in detail and applied to calculate and analyze the
performance of our detector. By comparison with a diode with only top contact
of gold, the polarization sensitivity of responsivity is greatly minimized in
our photodetector with sidewall coverage of gold. Much higher responsivities
for both polarizations are also achieved in a very broad wavelength range of
1.2-1.5 {\mu}m. Moreover, the Schottky contact is only 4 {\mu}m long, leading
to a very small dark current. Our design is very promising for practical
applications in high-density silicon photonic integration.
