Rhenium-based two-dimensional transition metal dichalcogenides, such as ReS2 and ReSe2, have attracted considerable interest for optoelectronic applications—including polarization-sensitive photodetectors—due to their weak interlayer coupling, strong in-plane anisotropy, and monolayer-like direct bandgaps. However, performance inconsistencies such as hysteresis, often induced by both intrinsic and extrinsic trap states, remain a challenge in TMD-based devices. In this study, we present a comparative analysis of the scattering mechanisms, hysteresis, and photoresponsivity \(\left( R \right)\) of ReS2 and ReSe2 phototransistors by examining their transfer characteristics under varying temperatures and illumination conditions. Trap-state distributions were systematically investigated using wavelength-resolved sub-bandgap illumination, which enables emission of carriers from deeper trap states. The ReS2 device exhibits electron–phonon scattering as the dominant transport mechanism, along with minimal hysteresis, attributed to a lower density of intrinsic traps with widely spaced trap states. In contrast, the ReSe2 device is characterized by charge-impurity scattering and pronounced hysteresis, arising from a higher trap density with closely spaced trap states. Additionally, ReSe2 displays a more gradual decline in the power-law exponent (γ) across a broader gate-voltage range and lower \(R\) compared to ReS2. These distinctions are linked to the higher formation energy of chalcogen vacancies in ReS2, which makes it more resistant to defect formation than ReSe2.
