Figure 1. Hybrid graphene–CQDs phototransistor with a transparent top-electrode.

(a) Schematic of device structure. (b) Optical image of a device used in the study. Device elements are labelled. Borders of graphene channel are highlighted in black. Active device area is located between the inner graphene probes, marked as V+ and V−. CQD layer is deposited on the active area and exceeds it in size to ensure its uniform coverage and prevent shorts between the ITO and graphene channel. Scale bar, 30 μm. (c) Schematic of phototransistor operation. Incident light creates electron–hole pairs in the CQD layer. Electrons remain in the CQD, while holes, driven by depletion on the interface with graphene, are transferred to the graphene channel and alter its resistance. Constant current is driven between source and drain electrodes, while voltage drop is measured between V+ and V− electrodes. Thus, the photo-induced change in resistance (or voltage drop) is measured with the highest accuracy excluding the resistance of the metal and graphene contacts.