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

ReS2 is a promising candidate for next-generation optoelectronic devices due to its direct bandgap and thickness-independent characteristics. However, when ReS2 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 ReS2 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 × 1012 to 6.5 × 1011 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 ReS2 without mica showed a 55% decrease in photocurrent after 35 days and a 75% decrease after 60 days. In contrast, ReS2 with mica exhibited only a 16% decrease after 35 days and a 43% decrease after 60 days. Finally, the rise time (tr) was reduced by approximately 13 s and the fall time (tf) 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 ReS2 devices.