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

Abstract

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.