[en] Full text: Two-dimensional (2D) van der Waals (vdW) heterostructures (HTS) allow the combination of properties from a variety of 2D materials and represent the fundamental platform for important solid-state device fabrication. However, the interlayer electron coupling is often governed by relatively weak long-range vdW interactions, thereby limiting practical applications. Herein, based on density functional theory, we demonstrate that an effective electron coupling can be created in 2D C₃B/C₃N vdW HTS. Monolayer C₃B and C₃N, which have been fabricated in recent experiments, are p- and n-typed doped large gap semiconductors, respectively. However, the formed vdW HTS exhibits novel Dirac fermion as presented in this work. Additionally, a large interlayer built-in electric field is generated in this HTS, leading to an intrinsic band inversion between pz orbital of B and N atoms. A simple tight-binding model with the nonzero interlayer hopping parameters is constructed and can well reproduce the electronic band structure. Compared to isolated C₃B and C₃N, the 2D C₃B/C₃N vdW HTS is very optically active with enhanced photocurrent production and displays broadened absorbance spectrum from the near infrared to the ultraviolet region. Our results demonstrate the importance of electron coupling in the modulation of materials properties of 2D vdW HTS and suggest a practical strategy to realize a strong electron coupling toward the realistic applications in nanoelectronics and photonics. (author)