This work presents a systematic TCAD-based investigation of an MoSe 2 /Si heterojunction photodetector for visible-light operation using Silvaco ATLAS. The influence of MoSe 2 thickness (0.65–3.25 nm) on band alignment, electric field distribution, quantum efficiency, responsivity, transient response, and frequency characteristics is analyzed. Interface defect states are incorporated using exponential tails and Gaussian trap distributions to evaluate their impact on carrier recombination and device performance. The monolayer device exhibits a peak interfacial electric field of ~2.5 × 10⁶ V/cm, yielding a responsivity of 0.26 A/W, an EQE of ~58%, a response time of ~1 µs, and a cutoff frequency approaching 1 MHz. Increasing thickness reduces peak electric field strength and carrier collection efficiency, while leaving the bandwidth nearly unchanged due to the dominance of the Si-side depletion region and the RC time constant. The results highlight thickness-controlled electric-field engineering as a key parameter for optimizing responsivity–speed trade-offs in ultrathin MoSe 2 /Si photodetectors. This study reveals a thickness-controlled trade-off between responsivity and speed. It identifies a thickness-independent bandwidth regime governed by Si-side depletion dynamics, providing new design guidelines for ultrathin MoSe 2 /Si photodetectors.
Gujari et al. (Fri,) studied this question.