Self-powered, broadband Ta₂NiSe₅/p-GaAs van der Waals heterojunction photodetector with high polarization sensitivity

The increasing demand for high-performance, low-power, and broadband photodetection in advanced optoelectronic applications-such as optical communication, imaging, sensing, and environmental monitoring-have driven significant interest in mixed-dimensional heterostructures. Here, we demonstrate a novel van der Waals heterojunction photodetector based on a Ta₂NiSe₅/p-GaAs architecture. By integrating two-dimensional (2D) Ta₂NiSe₅ nanosheets, which exhibit a narrow bandgap and high carrier mobility, with p-type GaAs possessing a low-lying Fermi level, a type-I band alignment is achieved. This configuration enables efficient separation of photogenerated carriers while suppressing interfacial recombination. The resulting device exhibits a broadband self-powered photoresponse ranging from 375 to 1310 nm. At 808 nm, it achieves a high responsivity of 10.14 A W^-1, a specific detectivity of 1.95 × 10¹³ Jones, and rapid temporal response (rise/fall times of 0.94/1.02 ms). Furthermore, the device demonstrates strong polarization sensitivity under linearly polarized illumination, with an anisotropy ratio of 4.38. These results underscore the potential of the Ta₂NiSe₅/p-GaAs heterojunction for the development of next-generation photodetectors with broadband, self-powered, and polarization-resolved capabilities.