Photoresponse of MoSe₂ Transistors: A Fully Numerical Quantum Transport Simulation Study

Phototransistors made with two-dimensional transition metal dichalcogenides (TMDs) have shown excellent potential for nanoscale optoelectronic applications. In this work, we perform fully numerical simulations to investigate photoresponse mechanisms in MoSe2 transistors, considering photoconductive and photogating (PG) effects. Our model implements PG by self-consistently solving a trapped charge distribution with electrostatics and transport in the channel. The results are in good agreement with the reported experimental device characteristics and explain the PG effect by quantifying potential barrier lowering and trapped carrier concentration upon illumination. We study the two mechanisms in isolation and reveal the dominance of the PG effect on the photocurrent at high gate voltages. Additionally, we show a trade-off between photoresponsivity and specific detectivity at different gate voltages and find that the gain of the phototransistor decreases with increased optical power density due to the saturation of trapped carriers. Finally, we show that photoresponsivity can be tuned over several orders of magnitude by varying trap-state energy, capture cross sections, total concentration of trap states, and recombination lifetime, all of which can be changed through material optimization. Our work highlights the underlying physics of photoresponse in TMD devices and presents a model which can be used for future device design.