Prediction and simulation of a potential barrier block in Van der Waals heterojunction photodetectors

The pBp structure can effectively suppress the dark current of a photodetector by blocking the majority of carriers. However, it is a big challenge to carry out large-scale simulation optimization for two-dimensional (2D) pBp heterojunction photodetectors due to a lack of the device models. Here, a numerical simulation model of the 2D pBp heterojunction was established based on the finite element method to solve this problem. Using this model, the spatial distribution of the energy band is clarified for each layer. The concentration of nonuniformly distributed electrons, induced by the incident light and bias voltage, is obtained by solving the diffusion and drift equations. The characteristics of the photocurrent and the dark current could be presented and the quantum efficiency could be calculated by counting the ratio of the number of carriers collected at the terminals and the carriers photogenerated. The material parameters could be modified for the optimization of the simulation and prediction. In using our model, a B P/M o S ₂/graphene photodetector was constructed, and the simulation results show that it works effectively under a reverse bias ranging from -0.3 to 0 V. The external quantum efficiency is 18%, while the internal efficiency approaches 85%. The doping in the barrier region definitely does not affect the dark current and the photocurrent. These results are similar to experimental results published earlier. In addition, with the BP bandgap width of 0.8 eV and incident wavelength of 1.7 µm, the dark current density predicted by the model could reach 3.3×10^-8 A/c m ², which is two orders lower than the reported 2D photodetectors at room temperature. This proposed model provides a way to design 2D pBp heterojunction photodetectors.