Pixel Geometry Effect on PbS Quantum Dot/Graphene Nanohybrid Broadband Photodetectors

Abstract Photodetectors based on colloidal quantum dots (QD)/graphene nanohybrids are quantum sensors due to strong quantum confinement in both QD and graphene. The optoelectronic properties of QD/graphene nanohybrids are affected by the quantum physics that predicts a high photoconductive gain and hence photoresponsivity ( R * ) depending on the pixel length ( L ) as R * ∝ L −2 . Experimental confirmation of the effect of the pixel geometric parameters on the optoelectronic properties of the QD/graphene photodetector is therefore important to elucidate the underlying quantum physics. Motivated by this, an array of PbS QDs/graphene nanohybrid photodetectors are designed with variable QD/graphene pixel length L and width ( W ) in the range of 10–150 µm for a study of R * , noise, and specific detectivity ( D * ) in a broad spectrum of 400–1500 nm. Intriguingly, R * exhibits a monotonic decreasing trend of 1/ L 2 while being independent of W , confirming experimentally the theoretical prediction. Interestingly, this geometric effect on the photoresponsivity seems to be partially compensated by that in noise, leading to D * independent of L and W at wavelengths in the ultraviolet‐visible‐near infrared range. This result sheds light on the quantum physics underlying the optoelectronic process in QD/graphene nanohybrids, which is important to the design of high‐quality QD/graphene photodetectors and imaging systems.