  We report the fabrication and characterization of a plasmonic metasurface
comprising electrically contacted sub-wavelength gold dipole nanoantennas,
conformally coated by a thin hafnia film, an indium tin oxide layer and a
backside mirror, forming metal-oxide-semiconductor (MOS) capacitors, for use as
an electrically-tunable reflectarray or metasurface. By voltage biasing the
nanoantennas through metallic connectors and leveraging the carrier refraction
effect in the MOS capacitors, our measurements demonstrate phase control in
reflection over a range of about 30 degrees, with a constant magnitude of
reflection coefficient of 0.5, and the absence of secondary lobes.
Comprehensive electromagnetic and quantum carrier models of the structure are
developed and are in excellent agreement with the measurements. The metasurface
holds promise for use as an optical phased array.
