  We report on a photodetector in which colloidal quantum-dots directly bridge
nanometer-spaced electrodes. Unlike in conventional quantum-dot thin film
photodetectors, charge mobility no longer plays a role in our quantum-dot
junctions as charge extraction requires only two individual tunnel events. We
find an efficient photoconductive gain mechanism with external
quantum-efficiencies of 38 electrons-per-photon in combination with response
times faster than 300 ns. This compact device-architecture may open up new
routes for improved photodetector performance in which efficiency and bandwidth
do not go at the cost of one another.
