Semiconducting THO-C₃N Monolayers for Ultrahigh Anisotropic Carrier Mobility

Biphenylene-based structures with semiconducting characteristics hold great promise for nanoelectronics owing to their intrinsically anisotropic charge transport. Yet, achieving semiconducting behavior in these systems remains challenging due to their inherent metallic nature. Here, we propose a precise site-specific N-doping strategy that drives a secondary electronic transition in net W, enabling the electronic properties transition from metal to Dirac semimetal and ultimately to semiconductor. This transition is governed by the synergistic interplay of structural distortion, band-filling, on-site energy differences, and symmetry. The optimized THO-C₃N-2 and THO-C₃N-3 semiconductors exhibit high carrier mobilities (exceeding 10³ cm² V^-1 s^-1) and pronounced mobility anisotropy, with THO-C₃N-2 achieving the highest electron mobility anisotropy ratio (2061.22) among reported 2D carbon nitride systems. This work not only establishes an effective band engineering paradigm for biphenylene-based materials but also offers promising candidates for directionally tailored nanoelectronic devices.