Programmable Bandgap in a Topological Semimetal Enables Zero‐Bias UV/NIR Dual Band Photodetection and Optical Encryption Applications

ABSTRACT

The monolithic integration of ultraviolet (UV) and near‐infrared (NIR) photodetection in a single device is fundamentally constrained by the inherent spectral crosstalk and architectural complexity of traditional heterostructures. Herein, we circumvent these limitations by introducing a paradigm‐shifting halide‐assisted defect‐compensation strategy that induces a semimetallic‐to‐semiconducting transition in topological 1T’‐MoTe ₂ , opening a tunable bandgap while preserving its intrinsically high carrier mobility. This material transformation enables a monolithic I‐1T’‐MoTe ₂ /GaN van der Waals heterojunction that achieves two mechanistically distinct, zero‐bias photodetection pathways within a single interface: a Schottky‐junction‐mediated UV response and a band‐engineered NIR absorption. The device delivers exceptional performance, including responsivities of 268 mA/W (350 nm) and 258 mA/W (750 nm), detectivities exceeding 10 ¹¹ Jones, and microsecond‐scale response speeds. Crucially, it overcomes the persistent trade‐off between high sensitivity and polarization discrimination, yielding a record polarization ratio of 8.55 in the NIR regime. We further validate its practical utility through robust demonstrations in encrypted optical communication and filter‐free multispectral imaging, underscoring its resilience and readiness for real‐world deployment. By establishing a material‐intrinsic route to programmable band‐structure engineering in topological systems, this work lays a transformative foundation for intelligent, polarization‐resolved photonic platforms and next‐generation secure sensing technologies.