Activation of Forbidden Raman Modes in Black Phosphorus–Metal Oxide Heterostructures for Self-Powered Photodetection

Abstract

Black phosphorus (BP) is an emerging two-dimensional (2D) material, but few of its vibrational modes remain forbidden under a perfect crystal symmetry. In this work, we investigate the activation of forbidden Raman modes in BP-Cu2O and BP-MoO3 heterostructures via edge-induced symmetry-breaking for self-powered photodetection. These modes are key elements in which symmetry-broken phonon states enable precise control and are leveraged for additional functionalities. Correspondingly, such symmetry-induced interfacial modulation directly influences charge transport characteristics and forms ohmic and Schottky contacts at the electrode and BP-metal oxide heterostructure interface. Importantly, both devices show the photoresponse from the ultraviolet (UV) to near-infrared (NIR) region due to the incorporation of the BP on the surface of the Cu2O and MoO3, which significantly affects the electrical properties because of the BP-Cu2O nanoflakes and BP-MoO3 nanoribbons, resulting in enhanced spectral absorption of the light onto the photoactive layer. Overall, the activation of symmetry-forbidden Raman modes in BP-metal oxide heterostructures reveals strong interfacial coupling and the formation of a built-in electric field, thereby enhancing charge separation efficiency and enabling high-performance self-powered photodetection.