Broadband antireflection with curved surface nano-pyramids for image sensing devices

Abstract

The reflection loss in imaging devices is one of the major drawbacks, which degrades efficiency resulting in lower responsivity. Since the reflected light is no longer available for conversion into electrons, it is very important to reduce the reflection from the top surface of the device as much as possible. Quarter wavelength and two index antireflection (AR) coatings have been developed to reduce reflection; however, these AR coatings are wavelength dependent and have not performed effectively in a broadband range. Attempts to make AR coating for broadband wavelengths by stacking multiple index AR layers result in thicker and expensive solutions, which still do not provide proper antireflection at all desired wavelengths. Moreover, the usage of AR coatings escalates material and fabrication costs of the device. We propose a novel nanostructure, which matches the refractive index of the device to that of free space to reduce reflection from the top surface, eliminating the use of AR coatings and hence reducing the device cost. It is shown via simulation that the proposed nanostructure effectively eliminates the reflection loss over the broadband spectrum of desired wavelengths e.g. Visible, Mid-wave IR (MWIR), Short-wave IR (SWIR) spectrums, opening various application opportunities.