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

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.