Laser Irradiation Effect on the p-GaSe/n-HfS₂ PN-Heterojunction for High-Performance Phototransistors

Two-dimensional (2D)-based PN-heterojunction revealed a promising future of atomically thin optoelectronics with diverse functionalities in different environments. Herein, we reported a p-GaSe/n-HfS₂ van der Waals (vdW) heterostructure for high-performance photodetectors and investigated the laser irradiation effect on the fabricated device. The fabricated 2D vdW heterostructure revealed a high photoresponsivity of 1 × 10⁴ A W^-1 with a photocurrent value of 377 nA due to unique type-II band alignment and enhanced surface potential under light illumination, which is further confirmed by density functional theory (DFT) calculations. Before laser irradiation, the device showed high field-effect mobility (μ_EF) of 26.37 cm² V^-1 s^-1, ON/OFF ratio of ∼10⁵, and threshold voltage swing (SS) of ∼463 mV dec^-1. With the exposure of 690 mW cm^-2 laser power density, μ_EF reached 204 cm² V^-1 s^-1, although ∼2 V ΔV_th shifts are observed along with the SS decreased to 175 mV dec^-1. Interestingly, the reduced SS shows better channel control of the fabricated device with laser power. Similarly, the ON/OFF ratio decreased to ∼1.29 × 10³. The results indicate that the creation of oxide trap charges at the interface of SiO₂ and PN-heterojunction layers was observed with voltage biasing and high laser power density. The degradation of electrical parameters is attributed to fewer interface trap charges per surface area of the device rather than direct damage in PN-heterojunction layers. Considering the excellent 2D electronic properties, these materials are better candidates for future high-radiation environments.