Ultra-Low Noise Photodetection in Exfoliated GaSe: Realizing Sub-Femtoampere Dark Currents for High-Detectivity Sensing

This study investigates the strategic development and optoelectronic characterization of ultra-low noise photodetectors fabricated from mechanically exfoliated gallium selenide ("GaSe" )nanosheets. While contemporary research in 2D optoelectronics predominantly targets high responsivity through internal gain mechanisms-often incurring significant noise penalties-this work adopts a “noise-centric” design philosophy to optimize the specific detectivity (D^* ). By integrating a ∼20" nm" thick "GaSe" flake within a precision-engineered metal–semiconductor–metal (MSM) architecture utilizing "Cr/Au" electrodes, we demonstrate an unprecedented dark current floor of 1" fA " at zero bias, maintaining sub-100" fA" stability up to a 2" V" operating regime. Spectroscopic analysis reveals a sharp responsivity cutoff at 620" nm" , correlating precisely with the 621" nm " photoluminescence (PL) emission peak, thereby confirming band-to-band transition dominance. Although the device yields a conservative responsivity of 2.7" mA/W" , the radical suppression of both shot noise and thermal noise components enables a specific detectivity that rivals state-of-the-art commercial silicon-based sensors. These findings underscore the viability of "GaSe " as a primary candidate for “green” electronics and battery-less, always-on remote sensing applications, where extreme noise minimization is the critical performance metric.