Anisotropic Raman Mapping and Strain‐Enhanced Optoelectronic Performance for Few‐Layer Suspended Black Phosphorus

Abstract 2D black phosphorus (BP) exhibits remarkable in‐plane anisotropy due to its puckered crystal structure, making it a promising candidate for anisotropic optoelectronic devices. However, convenient and rapid determining BP's anisotropic orientation remains a challenge. Here, a simple, cost‐effective, and non‐invasive method is presented to visualize the anisotropic orientation for suspended BP (S‐BP) using conventional Raman mapping. Multi‐aperture Raman mapping experiments demonstrate that S‐BP exhibits distinct elliptical patterns with long‐to‐short axis(l/s) ratios ranging from 1.18 to 1.11, whereas isotropic suspended molybdenum disulfide (S‐MoS 2 ) and graphene (S‐G) exhibit circular patterns. Angle‐resolved polarized Raman spectroscopy (ARPRS) results confirm that elliptical patterns for S‐BP correlate to anisotropic orientation, with long and short axes aligning to armchair (AC) and zigzag (ZZ) directions. The finite element method (FEM) reveals that the elliptical pattern originates from direction‐dependent stress distributions in S‐BP, with lower stress variation along the AC direction. The responsivity (R) of S‐BP‐based field‐effect transistors (FETs) reaches ≈1 A W −1 at 1064 nm in the AC direction, surpassing supported BP (Sup‐BP) FETs by 49% in R, 89% in response time, and 45% in recovery time. This integration of anisotropic orientation determination with strain engineering can be extended to other anisotropic 2D materials and opens new possibilities for tunable optoelectronic devices.