The area-arrayed dumbbell-shape Graphene Nano-Ribbons (GNRs) were fabricated by using chemical vapor deposition and photolithography technologies. The electronic behavior of the fabricated GNR-FET structure was evaluated for its photonic properties with an incident light intensity of 1-mW. The 200-nm wide GNRs structure showed metallic properties, while those with the width of 40 nm showed semiconductive properties as was expected. The light-induced photocurrent was observed in all the fabricated GNRs structures. The average photocurrent observed in the 2-mm wide graphene structure was 3.3 A/m2 and that observed in the 40-nm wide area-arrayed GNRs structure was 261 A/m2, respectively. Based on this photocurrent, the external photosensitivity of the 40-nm wide GNRs structure was about 2.6 × 105 A/W.m2 and this value was much larger than that of conventional Si-base solar cells. In addition, the effect of strain on the resistivity of GNRs was measured. Uniaxial tensile strain was applied to the area-arrayed GNRs structures with the width from 200 nm to 40 nm. The gauge factor obtained from the GNRs with the width wider than 100 nm was about 3, and that with the width of 40 nm was about 160. Therefore, highly-sensitive strain sensors can be realized by using GNRs thinner than 70 nm.
The optical properties and device physics of monolayer graphene under light is investigated in this study. In order to understand the change of the electronic behavior of graphene under light, it was necessary to study from the most fundamental layer with high quality. Thus, it became mandatory to develop a highly efficient, low-cost fabrication process for synthesis of high-quality monolayer graphene. The high-quality monolayer graphene was grown on a copper foil using a low-pressure chemical vapor deposition (LP-CVD) method at temperature of 1035°C for 10 minutes. Acetylene was used as the precursor gas for the synthesis of monolayer graphene. Thin Pt/Au films were, then, deposited on a silicon dioxide/silicon (SiO2/Si) substrate using electron beam (EB) lithography which served as source and drain electrodes of a transistor. The synthesized graphene was, then, transferred to a SiO2/Si substrate using PMMA (polymethyl methacrylate)-assisted method.
The quality of the synthesized graphene was validated using Raman spectroscopy. No significant D peak was observed in the Raman spectra of the synthesized graphene. This result validated the high quality of the transferred graphene. Next, the photo-sensitivity of G-FET was investigated under light source of color temperature of 2856 K at room temperature. The electron transfer characteristic of the fabricated G-FET was measured under dark and light illumination conditions. Finally, the graphene-based field effect transistor G-FET demonstrated an external photo responsivity of about 200 μA/W with a maximum photocurrent attained to be 0.2 μA at an incident luminance power of 1 mW. The active detection region of this sample was 1000 × 60 μm2.
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