Photoelectric Characteristic Study On Graphene Grown By CVD

Graphene, a member of carbon materials, is a two-dimensional (2D) latticework with sp2-hybridized carbon atoms bonded into a hexagonal structure. Because of its ultrahigh mobility and high transmittance, graphene shows promising application for microelectronics and photoelectric devices. In this dissertation, the growth of bilayer graphene films using (CVD) method on copper foils has been studied in detail. To further examine the electrical characteristic of the as-grown graphene, the prototype graphene field effect transistor (GFET) devices have been fabricated using graphene ribbons as channels by lithographic process and ion etching. Furthermore, Graphene/ZnO heterojunctions and photoelectric devices with the structure of Al/ZnO/Graphene/n-Si/Al have also been fabricated to investigate the opto-electric application for graphene.The main conclusions are as follows:(1)Bilayer graphene with high quality has been achieved using the CVD method. Raman measurements were used to characterize the graphene structures and XPS was measured to explore chemistry information of the prepared graphene. In the CVD process, certain effect factor for the graphene growth was studied. It is found that the flows of Ar and H2play significant roles on the quality of the prepared graphene. By reducing H2flow or increasing Ar flow, D defects of the graphene can be effectively decreased.(2)The vacuum annealing effects on the electrical properties of GFETs have been analyzed. Through annealing in vacuum (10-4Pa) at different temperature for several hours (100℃/4h,200℃/4h,300℃/4h,400℃/4h,300℃/20h), the GFET devices were found to have high hole concentration but obvious mobility change in graphene devices. The mobility for hole carriers is significantly increased by the increase of the annealing temperature from room temperature to200℃. When the annealing temperature is higher than200℃, the channel mobility of the GFET starts to degrade rapidly. In addition, the ON-OFF ratio of GFET gets lower when the temperature increases.(3)The photoluminescence (PL) and photoelectric properties of the Graphene/ZnO heterojunction were explored. The PL property of ZnO films annealed at different temperature (500℃-1000℃) is determined and found that ZnO film annealed at900℃ reveals the optimum property. By measuring the PL characterization of the as-received ZnO/Graphene heterojunction, it shows that graphene can have an enhancing effect on the luminescence intensity for the intrinsic exciton emitting in the ZnO film. The monolayer graphene on heterojunction indicates the optimum enhancement effect where the intensity of luminescence is twice of that in the ZnO film. Finally, photoelectric cells with the structure Al/ZnO/Graphene/n-Si/Al were fabricated with different ZnO thickness (15nm,30nm,45nm) on the Graphene/n-Si heterojunctions. The current-voltage characteristics demonstrate that graphene/ZnO heterojunction exhibits good rectifying and photoelectric effect. When ZnO layer is at the thickness of30nm, the cell performs the optimum photoelectric property.