Intraband quantum dots are degenerately doped semiconductor nanomaterials
that exhibit unique optical properties in mid- to long-wavelength
infrared. To date, these quantum dots have been only studied as lateral
photoconductive devices, while transitioning toward a vertically stacked
structure can open diverse opportunities for investigating advanced
device designs. Here, we report the first vertical intraband quantum
dot heterojunction devices composed of Ag2Se/PbS/Ag2Se quantum dot stacks that bring the advantage of reduced
dark conductivity with a simplified device fabrication procedure.
We discuss the improvement in the colloidal synthesis of Ag2Se quantum dots that are critical for vertical device fabrication,
identify an important process that determines the mid-wavelength infrared
responsivity of the quantum dot film, and analyze the basic device
characteristics and key detector performance parameters. Compared
to the previous generation of Ag2Se quantum dot-based photoconductive
devices, approximately 70 times increase in the mid-wavelength responsivity,
at room temperature, is observed.