Photovoltaic Modulation of MoS2 Transistors via Interfacial Photoelectron Injection in Pn-Si/MoS2/h-BN Heterostructures

Two-dimensional (2D) semiconductor transistors offer attractive optoelectronic functionality beyond the scaling limits of conventional silicon technology. However, conventional 2D phototransistors often suffer from limited photoresponse performance, high energy consumption, and unstable threshold voltage. To overcome these challenges, we demonstrate a photovoltaic modulated field-effect transistor based on a pn-Si/MoS2/h-BN heterostructure. Under visible illumination, photogenerated electrons accumulate near the pn-Si/MoS2 interface and are vertically injected into the adjacent MoS2 conduction channel. A current change from approximately 3.8 μA to 11.2 μA is observed when illumination is switched on during a gate-voltage sweep, corresponding to a switching-event current ratio of approximately 2.95. Concurrently, the device exhibits reversible current modulation during the recorded optical ON/OFF cycles. Wavelength-dependent measurements further elucidate a critical competition between injection-driven carrier enhancement and high-field suppression effects. First-principles calculations using monolayer MoS2/h-BN heterostructure models further show that electron doping increases the electrical conductivity of MoS2 by increasing the occupation of conduction-band states and improving carrier transport. These results demonstrate optical modulation in Si-supported MoS2 devices and motivate further investigation of the contributions from interfacial carrier transfer and photovoltaic gating.