van der Waals ZnO/HfSn₂N₄ Heterojunction with Exceptional Photoresponse for Photodetectors

Two-dimensional van der Waals heterojunctions represent a promising avenue for a spectrum of optoelectronic endeavors. Nonetheless, their deployment has been somewhat constrained by the suboptimal efficiency of the photocurrent generated. In this article, a ZnO/HfSn₂N₄ heterojunction is proposed to achieve high photoresponse efficiency. First-principles calculations are utilized to confirm that this heterojunction possesses thermal stability with a direct bandgap (1.36 eV). It exhibits a high light absorption coefficient and high carrier mobility (2.51 × 10³ cm² V^-1 s^-1), and biaxial strain has a significant effect on the modulation of the band structure. As the tensile strain increases, the bandgap changes nonlinearly, transitioning from a type-II to a type-I heterojunction. When compressive strain increases, the bandgap decreases. Quantum transport simulations are employed to calculate the density of states and transmission spectrum of the ZnO/HfSn₂N₄ model, verifying its excellent photoresponse (a photocurrent peak reaching 4.93 a₀²/photon and an extinction ratio peak of 75.1). It shows that the ZnO/HfSn₂N₄ heterojunction is a potentially efficient photodetector.