Broad spectrum high responsivity photodetector based on SiC-graphene transistor

Abstract

We report a photodetector based on SiC-graphene transistors with symmetrical source drain electrode, broad spectrum and high responsivity has been obtained. We measured the output characteristic curve under the illumination of 405nm wavelength with different power. As depicted in the diagram, both the dark and light I-V curves are straight lines across the original point, which indicates that the source drain electrode (Ti/Au) form good ohmic contacts with graphene, and it is not back to back schottky structures. The photoresponse current increases with the enlargement of light power. The responsivity varies with light power under 1.5v source drain bias is measured. It can be read apparently that the responsivity of epitaxial graphene is obviously higher than that of transferred graphene. Under the illumination from the light of 0.12mW power, the responsivity of the transferred graphene structure is 0.25A/W, while the responsivity of the epitaxial structure is close to 1A/W, which is almost an order of magnitude. We speculate that the buffer layer between the Si-face epitaxial graphene layer and the SiC substrate played a role in enhancing the interface photoelectric detection capability. The I-V curve under high-power light illumination of 450nm wavelength visible light shows that the responsivity is raised by an order of magnitude, and similar results under the illumination of 635nm wavelength visible light was obtained. We depicted the transfer characteristic curve under the control of the top gate structure. With the irradiation of 405nm wavelength light, the current drops and the dirac point shifts left Under the control of positive gate voltage. The current drops and the dirac point moves to the right under the control of the back gate structure. The dirac point is positive in the dark state, we speculate that the transition graphene is P-doped, the positive top gate voltage attracts electrons and neutralizes graphene, thus reaching the neutral point. With with the illumination, electrons transfer from SiC to graphene, and the graphene is further neutralized, leading to the left shifting of dirac point. The opposite results from the back gate modulation confirmed our previous analysis.