Embedded surface plasmon resonant disc arrays for improved MWIR sensitivity and increased operating temperature of PbSe photoconductive detectors

The infrared sensing market has experienced increased attention in recent years, due in large part to a widening of the application space from defense and research to commercial and consumer avenues. The uncooled market has been dominated by microbolometers, yet a recent resurgence of polycrystalline PbSe photoconductors could be the key to infrared photon detectors operating at room temperature. Typically, PbSe detectors are operated at 230 K, and can achieve sensitivity similar to its cryogenically cooled counterparts. In an effort to develop truly uncooled photon detectors, we have investigated surface plasmon resonant (SPR) structures for MWIR sensitivity enhancement of PbSe photoconductors. Au disc-shaped nanostructures were modeled to determine the required dimensions for a targeted resonance region between 3.5 μm to 4 μm. Finite element modeling (FEM) was then used to determine the effect of square disc arrays on the absorption of PbSe thin films. Modeled results suggest up to a three-fold increase in PbSe absorption in films with embedded structures. Square disc arrays made up of 500 nm and 1000 nm discs were patterned, fabricated, and embedded into sensitized polycrystalline PbSe thin films. FTIR spectra were collected to validate the model and determine the viability of SPR structures in a polycrystalline thin films. Based on FEM results, numerical models were constructed to predict photoconductor performance. Herein, we present the design, modeling, fabrication, and measured spectra of Au disc arrays embedded in PbSe films, as well as MWIR photoconductor performance predictions suggesting increased operating temperature with the utilization of SPR structures.