Schottky photodiodes based on mid-wavelength infrared intraband colloidal quantum dots - surface ligand and metal contact studies

There is an emergent need for low-cost, uncooled detectors operating in the mid-wavelength infrared. Here, we report the first Schottky junction diode that utilizes intraband Ag₂Se colloidal quantum dots as mid-wavelength infrared absorbers. These inexpensive, solution-processed Schottky devices exhibit orders-of-magnitude suppression of dark current compared to the photoconductors, while providing a greater fabrication simplicity compared to the barrier or p-n heterojunction devices. We highlight our findings on the role of the capping ligand in the detector performance parameters and discuss our metal contact studies to form rectifying junctions to the colloidal quantum dot films. The optimized Schottky devices show a favorable infrared responsivity of 0.1 A W⁻¹ and an uncooled specific detectivity of 10⁷ Jones. We also identify the present limitation of the device (1/f noise) and discuss potential paths toward future improvements.