Transferable Polycrystalline Diamond Membranes for Solar‐Blind Deep Ultraviolet Photodetectors

Abstract Solar‐blind deep ultraviolet (UV) photodetectors based on polycrystalline diamond membranes (PCDm) are promising for extreme‐environment optoelectronics owing to their wide bandgap, superior thermal conductivity, and mechanical resilience. Here, the correlation between surface properties and photodetection performance is systematically investigated by fabricating metal–semiconductor–metal photodiodes on three distinct PCDm surfaces: the as‐grown top surface (T‐PCDm), the nucleation bottom surface (B‐PCDm), and an etched bottom surface (EB‐PCDm). T‐PCDm exhibits the highest responsivity (0.55 A W −1 at 265 nm), large on/off ratio (650), and ultrahigh detectivity (≈1.4 × 10 12 Jones), attributed to its larger grain size, rougher morphology, and lowest sp 2 fraction, which enhance light trapping and carrier transport. B‐PCDm suffers from smaller grains and elevated sp 2 content, yielding suppressed photocurrent. EB‐PCDm demonstrates improved responsivity and the fastest time response among the three types of structures, reflecting its smoother morphology and reduced trap states after plasma etching. Furthermore, flexible devices on polyimide substrates show stable responsivity under tensile and compressive strains, underscoring the mechanical robustness of PCDm. The work highlights the critical interplay between microstructure, chemical purity, and surface engineering in dictating optoelectronic properties, and establishes freestanding PCDm as a versatile platform for high‐performance, flexible, solar‐blind UV photodetectors.