Comparative analysis of charge-trap sensitivity and stability in MoTe₂ and WS₂ field -effect transistors

Field-effect transistors (FETs) incorporating two-dimensional transition metal dichalcogenides (TMDs), such as MoTe₂ and WS₂, often suffer from significant hysteresis and fluctuations in the threshold voltage. These instabilities originate not only from charge trapping at the oxide–semiconductor interface but also from trap states located within the bulk of the semiconductor, primarily caused by intrinsic defects such as chalcogen vacancies. In this study, we performed a comparative analysis of the hysteresis behavior and trap-mediated charge-transport mechanisms in MoTe₂ and WS₂ FETs. The transfer characteristics were measured under various gate-voltage sweep conditions, temperatures, and wavelength-dependent optical excitations to extract the effective trap density and evaluate its impact on device performance. MoTe₂ devices exhibited stronger hysteresis and a more pronounced temperature dependence than WS₂ devices, indicating a higher density of thermally active and bulk-localized trap states. In MoTe₂, although the field-effect mobility increased with gate bias, the rate of enhancement significantly decreased as trapped charge accumulated. In contrast, WS₂ exhibited a more stable and gradual mobility enhancement with less sensitivity to the accumulation of trapped charges. Photoexcitation experiments revealed that the bulk trap states in MoTe₂ are energetically concentrated, whereas those in WS₂ are more evenly distributed. These findings indicate that WS₂ is a more robust and reliable channel material for trap-sensitive FET applications, whereas MoTe₂ requires refined interface and bulk defect engineering to ensure consistent operation.