Graphene and PbS quantum dot hybrid vertical phototransistor

A field-effect phototransistor based on a graphene and lead sulfide quantum dot (PbS QD) hybrid in which PbS QDs are embedded in a graphene matrix has been fabricated with a vertical architecture through a solution process. The n-type Si/SiO₂ substrate (gate), Au/Ag nanowire transparent source electrode, active layer and Au drain electrode are vertically stacked in the device, which has a downscaled channel length of 250 nm. Photoinduced electrons in the PbS QDs leap into the conduction band and fill in the trap states, while the photoinduced holes left in the valence band transfer to the graphene and form the photocurrent under biases from which the photoconductive gain is evaluated. The graphene/QD-based vertical phototransistor shows a photoresponsivity of 2 × 10³ A W^-1, and specific detectivity up to 7 × 10¹² Jones under 808 nm laser illumination with a light irradiance of 12 mW cm^-2. The solution-processed vertical phototransistor provides a new facile method for optoelectronic device applications.