Negative photoconductivity-driven interface engineering in topological insulator BiSb/InP heterojunctions for switchable ultraviolet-visible broadband photodetection

This study addresses the critical challenge of developing broadband ultraviolet-visible-infrared photodetectors for optical communication systems. While conventional indium phosphide (InP)-based detectors are primarily limited to short-wave infrared bands, their response in the ultraviolet-visible spectrum remains substantially inadequate. To overcome this limitation, we demonstrate an innovative heterojunction architecture by integrating a topological insulator BiSb with an InP substrate. Through the (012)-oriented preferential growth of a BiSb layer on InP, we achieved a type-II band alignment that leverages Dirac surface states for efficient carrier transport and tunable narrow-bandgap broadband light capture. The implementation of a negative photoconductance (NPC) regulatory mechanism enables selective suppression of low-energy photocarrier trapping at BiSb surface states. Density functional theory (DFT) calculations elucidate the interfacial physics, revealing that a 0.18 eV interfacial dipole optimizes carrier transport pathways. Experimental results show 0.4/1.76 ms rise/fall times at 650 nm and a photocurrent drop to 9.35 × 10^-7 A at 365 nm (3 V bias) relative to the dark current, achieving dual-band synergy with responsivities of 5.75 mA/W@365 nm and 10 mA/W@650 nm. This work pioneers the integration of topological surface state engineering with NPC modulation strategy on industrial InP platforms, providing a scalable solution for high-sensitivity multispectral imaging and high-speed optical communication systems.