Characterization of bulk trap density using fully I-V-based optoelectronic differential ideality factor in multi-layer MoS₂ FETs

Molybdenum disulfide (MoS₂) has excellent optoelectronic properties, chemical stability, and a two-dimensional (2D) structure, making MoS₂ a very versatile field-effect device material. Herein, we characterize MoS₂ and utilize a photo-responsive I-V technique for extracting the energy distribution of the bulk traps in multi-layer MoS₂ field effect transistors (FET). This method uses the differential ideality factor in both dark and light conditions. The differential ideality factor enables the efficient quantitative extraction of the device trap density by considering the nonlinear characteristics of the subthreshold region (V_ON < V_GS < V_T). To accurately differentiate between the sub-bandgap traps and the interface traps near the conduction band, near-infrared light (λ= 1530 nm) optical illumination was used for the light state characterization. The bulk trap densities under dark state and light state conditions were derived for multi-layer (7-layer and 9-layer) MoS₂ FET channels, and the influence of light illumination and overall multi-layer thickness on the bulk trap density was confirmed. The accurate extraction of the trap density enables the design of MoS₂ FETs with long-term stability and high optoelectronic performance.