Systematic Phosphorus‐Driven Structural and Field Engineering of n‐a‐Si:H for Flexible n‐a‐Si:H/Te Near‐Infrared Photodetectors

ABSTRACT Flexible near‐infrared (NIR) photodetectors are promising for optical communication, imaging, and wearable sensing, yet simultaneously achieving high responsivity, low dark current, and mechanical robustness remains challenging. Here, we report a flexible n ‐type hydrogenated amorphous silicon/tellurium (n‐a‐Si:H/Te) heterojunction photodiode enabled by systematic control of the phosphine‐to‐silane dilution ratio and the introduction of a front‐surface‐field (FSF) layer. At the optimized phosphine dilution (P ratio = 25%), the n‐a‐Si:H film exhibits reduced defect density and improved structural ordering, forming an electronically coherent heterojunction with crystalline Te. The resulting device shows pronounced diode rectification and a strong photoresponse at 1050 nm, driven by efficient Te absorption and built‐in‐field‐assisted carrier separation. Furthermore, inserting a 10‐nm‐thick heavily doped n‐a‐Si:H FSF layer between the transparent conductive oxide and the active layer enhances band bending and suppresses interfacial recombination, leading to 5.1‐ and 2.6‐fold improvements in responsivity and detectivity, respectively. External quantum efficiency analysis confirms that the performance enhancement originates from electrical field modulation rather than optical effects. The FSF‐engineered device exhibits broadband operation (400–1600 nm) and maintains over 90% of its initial responsivity after 4000 bending cycles, demonstrating a robust strategy for high‐performance flexible NIR optoelectronics.