  Many consumer technologies and scientific methods rely on photodetection of
infrared light. We report a Schottky photodetector operating below silicon's
band gap energy, through hot carrier injection from a nanoscale metallic
absorber. Our design relies on simple CMOS-compatible 'bottom up' fabrication
of fractally nanostructured aluminium films. Due to the fractal nature of the
nanostructuring, the aluminium films support plasmonically enhanced absorption
over a wide wavelength range. We demonstrate two orders of magnitude
improvements of responsivity, noise-equivalent-power, and detectivity as
compared to bulk metal, over a broad spectral and angular range. We attribute
this to momentum relaxation processes from the nanoscale fractal geometry.
Specifically, we demonstrate a direct link between quantum efficiency
enhancement and structural parameters such as perimeter to surface ratio.
Finally, our devices also function as bulk refractive index sensors. Our
approach is a promising candidate for future cost effective and robust short
wave infrared photodetection and sensing applications.
