Modifications of spheroid plasmonic particle geometry for enhancement of ultrathin semiconductor infrared detectors

We consider the enhancement of the specific detectivity of semiconductor infrared detectors utilizing a redshifted plasmonic light concentrator. To this purpose submicrometer-sized doped transparent conductive oxide particles with different shapes were used, embedded within high dielectric permittivity medium. The whole structure was topped with a graded antireflective layer. Localized surface plasmon resonance ensures high field localization around the plasmonic particles and directly beneath them, which translates into high density of optical energy within the detector active region. We investigate the possibilities to tune the particle shape and size in order to maximize the photodetector optical energy input, i.e. to maximize the detector external quantum efficiency. We perform ab initio simulation of the optical response utilizing the finite element method, starting with spherical particles and then extending this to include spheroids and sub-micrometric plates. As an illustrative example, we analyze a mercury cadmium telluride infrared detector with an ultrathin active epitaxial active layer. An increase in external quantum efficiency is obtained for non-spherical particles compared to the spherical ones. This can be used to offset a decrease in the optical path/internal quantum efficiency. Plasmonic localization is convenient for this since optical energy density is strongly localized close to the illuminated surface, thus ensuring a large decrease of the total detector volume and therefore suppressing the generation-recombination noise levels which are proportional to the device volume. Our results show that it is possible by this approach to realize an uncooled semiconductor detector for mid-wavelength infrared range with its specific detectivity strongly increased compared to the conventional devices