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

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*proportional to 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 mu m 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/L2 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. A study on the effect of channel geometry on quantum dot/graphene nanohybrid photodetector noise and figures of merit. The results indicate that responsivity and noise are geometry-dependent and precisely cancel out to achieve a geometry-independent detectivity. image