Synergistic Pyro‐Phototronics and Structural Anisotropy in CsAg ₂ I ₃ /GaN Heterostructures for High‐Performance Polarization‐Sensitive UV Photodetectors

ABSTRACT Ultraviolet photodetectors capable of spectral selectivity, self‐powered operation, and polarization sensitivity are vital for next‐generation secure communication and sensing, yet their progress is hampered by material instability, interfacial losses, and the difficulty of multifunctional integration. Here, we report a groundbreaking CsAg ₂ I ₃ /GaN van der Waals (vdWs) heterojunction that uniquely integrates in‐plane structural anisotropy, pronounced pyro‐phototronic effect, and atomically sharp interface engineering. The CsAg ₂ I ₃ single‐crystals, synthesized via chemical vapor deposition, exhibit a wide‐bandgap (∼3.38 eV), strong second‐order nonlinear response, and remarkable pyroelectricity, overcoming the stability and symmetry limitations of conventional perovskites and inorganic wide‐bandgap semiconductors. The CsAg ₂ I ₃ /GaN device delivers record‐breaking performance: an ultralow dark current of 0.3 pA, high responsivity of 0.28 A/W, specific detectivity of 1.7 × 10 ¹² Jones, and ultrafast response speeds of 16/21 µs, outperforming most state‐of‐the‐art perovskites and wide‐bandgap photodetectors. Crucially, the pyro‐phototronic effect amplifies polarization sensitivity, achieving an unprecedented dichroic ratio of 10.5 under bias, the highest reported for all‐inorganic perovskite systems and other competitors. The device also demonstrates exceptional operational stability and robust performance in an information‐splitting encryption system, validating its real‐world applicability. This work establishes a new paradigm for synergizing pyro‐phototronics and structural anisotropy in heterostructures, enabling a versatile platform for high‐performance, self‐powered, polarization‐sensitive optoelectronics.