Ultrafast Dynamics and Self-Powered High-Responsive Broadband Ultraviolet Photodetection in Topological Bi ₂ Se ₃ /p-GaN Heterojunction

Ultraviolet (UV) radiation has a variety of impacts, affecting human health, agricultural productivity, and the integrity of materials across diverse environments. In the modern era, self-powered UV photodetectors provide detection of UV radiation enabled by the photovoltaic effect without any power consumption. Here, topological Bi 2 Se 3 thin film was deposited using the magnetron sputtering technique on p-GaN/sapphire (0001) substrate for multifunctional study of magneto-transport under 2 to 100 K temperature, self-powered broadband high-responsive UV photodetection, and ultrafast charge carrier dynamics properties. The magneto-transport analysis reveals weak antilocalization in Bi 2 Se 3 /p-GaN, with a coherence length of ∼187 nm at 2 K, confirming the presence of topological surface states. Transient absorption spectra of the Bi 2 Se 3 /p-GaN heterojunction reveal oscillations attributed to the Se–Se interface, along with a notably faster carrier lifetime from the visible to near-infrared spectrum region. Under self-powered conditions, the photodetector exhibits remarkable responsivity, achieving ∼1.9 × 10 2 mA/W at 255 nm (UV–C), ∼2.0 × 10 2 mA/W at 295 nm (UV–B), and an impressive ∼1.3 × 10 3 mA/W at 340 nm (UV–A) illumination, highlighting its superior sensitivity across the UV region. At 5 V bias, it achieves a high UV–A responsivity of ∼1.1 × 10 4 A/W which is ∼1.2 × 10 3 fold higher than pristine p-GaN/sapphire. The strong built-in electric field and high-mobility surface states in the Bi 2 Se 3 /p-GaN heterojunction facilitate efficient charge separation and rapid transport, enabling self-powered operation and superior photodetection performance, and providing valuable insights for the design of next-generation high-performance photodetectors.