Abstract
Graphene-based optoelectronic devices have attracted much attention due to their broadband photon responsivity and fast response time. However, the performance of such graphene-based photodetectors is greatly limited by weak light absorption and low responsivity induced by the gapless nature of graphene. Here, we achieved a high responsivity above 103 AW−1 for Ultraviolet (UV) light in a hybrid structure based phototransistor, which consists of CVD-grown monolayer graphene and ZnSe/ZnS core/shell quantum dots. The photodetectors exhibit a selective photo responsivity for the UV light with the wavelength of 405 nm, confirming the main light absorption from QDs. The photo-generated charges have been found to transfer from QDs to graphene channel, leading to a gate-tunable photo responsivity with the maximum value obtained at VG about 15V. A recirculate 100 times behavior with a good stability of 21 days is demonstrated for our devices and another flexible graphene/QDs based photoconductors have been found to be functional after 1000 bending cycles. Such UV photodetectors based on graphene decorated with cadmium-free ZnSe/ZnS quantum dots offer a new way to build environmental friendly optoelectronics.
Highlights
Graphene is a promosing 2D material for optoelectronics[1,2,3] and photodetection applications[4,5,6] due to its broad absorption bandwidth, excellent carrier transport properties and good flexibility for stretchable and wearable electronics[7,8]
The scanning electron micrograph (SEM) image of this device is shown in Fig. 1b, and the inset is the SEM image of a single ZnSe/ZnS quantum dots (QDs) in a spheroidal shape on the graphene channel, indicating a core-shell structure of ZnSe/ZnS QDs
In order to furtherly characterize the size of ZnSe/ZnS QDs, the transmission electron microscope (TEM) image of the QDs is shown in Fig. 1c with the scale bar of 10 nm and 5 nm, respectively
Summary
Graphene is a promosing 2D material for optoelectronics[1,2,3] and photodetection applications[4,5,6] due to its broad absorption bandwidth, excellent carrier transport properties and good flexibility for stretchable and wearable electronics[7,8]. Great progress has been made in the synthesis of QDs, and a large number of high quality QDs, such as CdSe, CdTe and CdS QDs, have been successfully synthesized by organometallic and aqueous approaches[19] Their efficient emissions are mostly limited in the range from the green to near-infrared spectral window due to a narrow band gap, which limits the applications in short-wave band[20]. The synthesis methods for such ZnSe/ZnS core/ shell quantum dots have been widely discussed and this class of materials has been applied as emitting materials in blue QD-LEDs due to their narrow emission peak and wavelength tunability[25,26,27] Their optoelectrical properties and potential applications in photodectors are rarely reported. The ligand capping the surface of QDs, which is used to gurantee the stablity of QDs, was found to have an impact on the photo responsivity of QDs, especially the response/recovery time, due to its role in charger transfer process between graphene and QDs
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