Shortwave Infrared Photodetection with oCVD Polythiophene.

Shortwave infrared (SWIR, λ = 1-3 µm) photodetectors typically use compound semiconductors that are fabricated using high-temperature epitaxial growth and require active cooling. New technologies that overcome these constraints are the focus of intensive current research. Herein, oxidative chemical vapor deposition (oCVD) is used for the first time to create a room temperature, vapor-phase deposited SWIR photoconductive detector with a unique tangled wire film morphology that detects nW-level photons emitted from a 500 °C cavity blackbody radiator-a rarity for polymer systems. A new, window-based process that greatly simplifies device fabrication is used to construct doped polythiophene-based SWIR sensors. The detectors feature an 8.97 kΩ dark resistance and are limited by 1/f noise. They feature an external quantum efficiency (gain-external quantum efficiency) product of 395% and have a measured specific detectivity (D*) of 106 Jones, with the potential to reach D* = 1010 Jones after 1/f noise is minimized. Still, the measured D* is only a factor of 102 lower than a typical microbolometer and after optimization, the newly described oCVD polymer-based IR detectors will be in a category competitive with commercially available, room temperature lead salt photoconductors and within reach of room temperature photodiodes.

Plasmonic enhancement of the two photon absorption cross section of an organic chromophore using polyelectrolyte-coated gold nanorods.

The effect of plasmonic enhancement on the two-photon absorption cross section of organic chromophores attached to polyelectrolyte-coated gold nanorods was investigated. The magnitudes of such enhancements were confirmed using single and two photon excitations of the chromophore molecules bound to polyelectrolyte-coated gold nanorods. By synthesizing two-, four-, six-, and eight-polyelectrolyte layer coated nanorods of a particular aspect ratio, the distance dependence of the evanescent electromagnetic field on molecular two-photon absorption was observed. Enhancements of 40-fold were observed for the chromophores nearest to the surface.