Ultrahigh Responsivity in Graphene-ZnO Nanorod Hybrid UV Photodetector

Ultraviolet (UV) photodetectors based on ZnO nanostructure/graphene (Gr) hybrid-channel field-effect transistors (FETs) are investigated under illumination at various incident photon intensities and wavelengths. The time-dependent behaviors of hybrid-channel FETs reveal a high sensitivity and selectivity toward the near-UV region at the wavelength of 365 nm. The devices can operate at low voltage and show excellent selectivity, high responsivity (R_I), and high photoconductive gain (G). The change in the transfer characteristics of hybrid-channel FETs under UV light illumination allows to detect both photovoltage and photocurrent. The shift of the Dirac point (V _Dirac) observed during UV exposure leads to a clearer explanation of the response mechanism and carrier transport properties of Gr, and this phenomenon permits the calculation of electron concentration per UV power density transferred from ZnO nanorods and ZnO nanoparticles to Gr, which is 9 × 10¹⁰ and 4 × 10¹⁰ per mW, respectively. The maximum values of R_I and G infer from the fitted curves of R_I and G versus UV intensity are 3 × 10⁵ A W^-1 and 10⁶, respectively. Therefore, the hybrid-channel FETs studied herein can be used as UV sensing devices with high performance and low power consumption, opening up new opportunities for future optoelectronic devices. The novelity of the UV phototransistor for UV detection is the combination of ZnO nanostructure for the UV absorption and Gr channel for charge transport to obtain excellent selectivity, ultrahigh responsivity, photoconductive gain, and low noise. The shift of Dirac point under UV light illumination gives clearer explanation on the responsive mechanism and carrier transport property of Gr and capability of phototransistor detecting both photocurrent and photovoltage.