Ligand-induced charge transport modulation and enhanced photoresponse in hybrid MoS2/quantum dot phototransistors

Mix-dimensional heterostructures of colloidal quantum dots (QDs) and two-dimensional (2D) layered materials have attracted growing interest in photodetection due to the combination of high optical absorption and superior charge transport characteristic. However, the QD sensitizing layer usually introduces uncontrolled doping to the 2D materials originating from the capping ligands, which deteriorates the gate modulation capability and interfacial charge transfer efficiency. In this work, we demonstrated that the photoresponse of MoS2/QD hybrid phototransistor was greatly enhanced by selecting ligand treatment strategy. The carrier concentration and mobility in MoS2 could be effectively tuned via surface doping of 3-mercaptopropionic acid ligand, resulting in high on-off current ratio and low dark current of around 10 pA. The signal-to-noise ratio was improved by three orders of magnitude compared to the pristine MoS2 devices, indicating a dramatically enhanced photoresponse sensitivity. The specific detectivity reached 3.1 x 1013 Jones at the illumination power of 2.3 mW/cm2. The photoresponse speed of the hybrid device was enhanced by about 100 times, owing to the effective interfacial charge transfer which was revealed by the photoluminescence quenching and optoelectrical characterizations. Our work may push a new path to design the interface of mix-dimensional heterostructure and develop high-performance electronic and optoelectronic devices.