Understanding Trap Effects on Photoresponse Kinetics of ReS₂ Phototransistors and Stability Enhancement by Mica Passivation: Implications for High-Stability Photodetector

ReS 2 is a promising candidate for next-generation optoelectronic devices due to its direct bandgap and thickness-independent characteristics. However, when ReS 2 photodevices are measured in ambient conditions, the photoresponse is relatively slow, ranging from several tens to hundreds of seconds. Several previous studies suggest that the slow photoresponse in low-dimensional nanomaterials is caused by surface traps formed by the adsorption/desorption of molecules. While these traps negatively affect the device by slowing down the photoresponse, they can also induce a photogating effect that can enhance the photocurrent generation. Herein, we fabricated two field-effect transistors (FETs) on the same ReS 2 channel with and without mica as a passivation layer and compared their electrical and optical properties over a period of 60 days. The introduction of mica improved the subthreshold swing (SS) and reduced the trap density from 1.4 × 10 12 to 6.5 × 10 11 cm –2 eV –1 . Additionally, responsivity improved from 485 to 824.3 A/W, and the overall degradation rate was reduced by 6 times over 60 days. Specifically, pristine ReS 2 without mica showed a 55% decrease in photocurrent after 35 days and a 75% decrease after 60 days. In contrast, ReS 2 with mica exhibited only a 16% decrease after 35 days and a 43% decrease after 60 days. Finally, the rise time ( t r ) was reduced by approximately 13 s and the fall time ( t f ) was significantly shortened by 140 s. These findings demonstrate that using a mica passivation layer can improve both the stability and the performance of optoelectronic ReS 2 devices.