In-plane anisotropy-driven directional charge transport in van der Waals p-n heterojunctions.

Low-symmetry two-dimensional (2D) van der Waals (vdW) materials enable anisotropic charge transport, crucial for polarization-sensitive optoelectronics. In this study, a p-GeS/n-MoS2 heterostructure diode is investigated, where the anisotropic band dispersion of GeS, revealed by angle-resolved photoemission spectroscopy (ARPES), governs directional charge flow. Angle-resolved Raman spectroscopy confirms the crystallographic orientation, and transport measurements in GeS field-effect transistors (FETs) show a mobility anisotropy of ∼3.4. The heterojunction exhibits orientation-dependent diode characteristics, anti-ambipolar transport, and a type-II band alignment, leading to anisotropic optoelectronic response. These findings establish a pathway for utilizing electronic anisotropy in vdW heterostructures for energy-efficient rectification.