Redshift by Design for Plasmonic Enhancement of Ultrathin Infrared Detectors

Abstract

In order to maximize sensitivity and specific detectivity of photodetectors, one has to ensure optimal light concentration within the active area. We considered light trapping based on surface plasmon resonance (SPR) in infrared detectors for night vision purposes. We investigated redshifting by the replacement of metal with transparent conductive oxides (TCO) like indium tin oxide and zinc oxide. We considered nanoparticle fillers embedded in a thin dielectric host with increased relative permittivity and located at the detector surface. We used finite element method to perform optimization of our plasmonic light trapping structures. Regarding the infrared detectors, we considered epitaxial mercury cadmium telluride devices with a typical active layer thickness of 4-8 micrometers. Our results show that sensitivity and specific detectivity of narrow-bandgap detectors can be significantly enhanced. Even thinner active areas than those conventionally used can be used. Since the overall level of intrinsic noise in a night vision detector (especially generation-recombination noise due to Auger processes) is dependent on the volume of the active region, in our case this noise is suppressed by the same mechanism that ensures sensitivity enhancement. Thus additional improvement of specific detectivity is achieved, which allows for higher operating temperatures of night vision photodetectors.