Highly Effective Photodetectors Based On Two-dimensional Nano-materials

In recent years, optoelectronic devices based on two-dimensional nano-materials, such as graphene and transition metal dichalcogenides have drawn a lot of attention. Because of their unique electrical and optical properties, two-dimensional nano-materials show great potential in the next generation of micro/nano electronic area. The main propose of our research is to find an effective way to improve the performance of graphene and MoS2 based phototransistors. We exploit other two nano-materials, Bi2Te3 nano-plates and graphene quantum dots (GQDs), to fabricate heterostructure□ devices:graphene-Bi2Te3 heterostructure photodetector and MoS2-GQDs photodetectors.1. Broadband graphene-Bi2Te3 heterostructure photodetector.From the former reports, a big shortcoming of graphene based photodetection devices is low responsivity (10-2-10-3 AW-1), which is caused by the gapless nature of graphene. We proposed a new approach to solve this problem, combing graphene with another small band gap nano-material (Bi2Te3). Due to the effective photocarrier generation and transfer at the □ interface between graphene and Bi2Te3, the device photocurrent can be effectively enhanced. Our results show that the graphene-Bi2Te3 photodetector has much higher photoresponsivity (35 AW-1 at a wavelength of 532 nm), as compared to the pure monolayer graphene-based devices. Moreover, the detection wavelength range of our device is further expanded to near-infrared (980 nm) and telecommunication band (1550 nm).2. Photodetector based on large area MoS2 film synthesized by chemical vapor deposition.We have achieved highly effective photodetection using large area MoS2 film (synthesized by chemical vapor deposition). The responsivity of our device is as high as 800 AW-1, which is comparable to the best results of ever-reported MoS2 photodetectors. But the response time of our device is too slow, which might be caused by the charge traps and impurities induced during growth process.3. Highly responsive MoS2 photodetectors enhanced by graphene quantum dotsIn order to overcome the major shortcoming of our MoS2 device and to further improve the photoresponse performance, we exploit another new nano-material, graphene quantum dots. It has great photon absorption and photoluminescence properties, and short carrier lifetime. We have fabricated MoS2-GQDs Van der Waals heterostructures, and using this new material for photodetection. Our heterostructure phototransistor has achieved great photoresponse performance. Not only we have increased the device response time for 300 times, but also we demonstrate a higher responsivity (～104 AW-1) and photoconductive gain (107) of our device.