Ultrathin high efficiency photodetectors based on near field enhanced optical absorption

Optical absorbers, comprising a thin semiconductor layer put between two transparent ones in close proximity of a subwavelength grating, are considered. These structures with no back mirror only mimic resonant cavity enhanced photodetector, being an order of magnitude thinner. It is argued that properly designed grating can assist the light confinement by near field microcavity resonance rather than by a mirroring. Tolerant designs to attain nearly 100% optical absorption at a predefined wavelength are demonstrated, and the near-field enhancement of the absorption is confirmed.