Broadband Phototransistors Enabled by Dual Transport Channels in Topological Insulator Bi ₂ Te ₂ Se

Topological insulators (TIs), characterized by insulating bulk states and metallic surface states hosting Dirac Fermions, exhibit remarkable nonlinear, optical, and optoelectronic properties. Owing to their narrow bandgaps and gapless surface conduction channels, TI-based phototransistors demonstrate high responsivity, low dark currents, and broadband spectral responses. However, the limited diversity of the reported TI materials has constrained their application in high-performance broadband photodetectors. Here, we report the growth of high-quality two-dimensional layered Bi₂Te₂Se via chemical vapor transport and systematically investigate its electronic and optoelectronic properties. Field-effect transistors (FETs) based on Bi₂Te₂Se show an impressive on/off current ratio of ∼10³ and a carrier mobility of 20.9 cm²V^-1s^-1. Notably, the devices exhibit a dual-channel transport mechanism, which relies on the synergy between the topological surface states, providing high-mobility pathways for rapid response (∼1.3 μs), and the thermally activated bulk carriers, which can be effectively depleted by gating to suppress the dark current. Furthermore, Bi₂Te₂Se phototransistors exhibit broadband photodetection across the visible to infrared range (450-1550 nm), achieving a peak responsivity of 155 A/W and a specific detectivity of 2.1 × 10¹⁰ Jones under 700 nm illumination. These results highlight the potential of layered Bi₂Te₂Se as a promising platform for next-generation broadband and high-speed optoelectronic devices.