Temperature‐Dependent Conduction and Gate‐Tunable Photoresponse in Graphene Photodetectors

Graphene photodetectors are promising candidates for broadband and high‐speed optoelectronics, yet tunable photoconductive behavior without junction engineering remains elusive. Here, we report gate‐controlled switching between positive and negative photoconductance in graphene field‐effect transistors (GFETs) fabricated on Si/SiO2 with Si3N4 passivation using a CMOS‐compatible process. Temperature‐dependent transport measurements (77–327 K) reveal impurity‐limited mobility at low temperatures and phonon‐dominated scattering at elevated temperatures, alongside pronounced hysteresis attributed to interfacial charge trapping and adsorbates. Under illumination, the devices exhibit a sublinear photocurrent dependence on incident power and saturation at higher intensities, consistent with a charge trap‐mediated photogating effect. Remarkably, the application of a back‐gate voltage induces a reversible transition from positive to negative photoconductance in the absence of heterojunctions. This behavior is attributed to the interplay of photogenerated carrier trapping at the graphene/SiO2 interface, adsorbate‐mediated charge transfer, and gate‐induced Fermi level modulation, which collectively govern carrier density and scattering. These results establish a simple platform for electrically tunable photoconductance in graphene and provide new insights into interfacial effects governing photogating, enabling low‐power and multifunctional optoelectronic devices.