Enhanced electronic transport and near-infrared photodetection in multilayer Bi-doped InSe

Two-dimensional (2D) indium selenide (InSe) is a promising semiconductor for next-generation electronic and near-infrared (NIR) photonic devices. However, its practical performance is constrained by low intrinsic carrier concentration, limited NIR absorption, and contact-induced transport barriers. Here, we systematically investigate the electronic transport and NIR optoelectronic properties of multilayer InSe field-effect transistors (FETs) enabled by bismuth (Bi) doping. Structural and spectroscopic analyses indicate that the Bi doping preserves the layered crystal framework of InSe, while simultaneously altering the microscopic optical and electronic properties through local atomic rearrangement and energy band engineering. Owing to the increased carrier concentration, Bi-doped InSe (Bi-InSe) FETs exhibit a substantially enhanced field-effect mobility of 429 cm2 V−1 s−1, exceeding that of intrinsic InSe devices. When operated as NIR phototransistors, Bi-InSe devices deliver significantly higher photocurrent, responsivity (up to 4.82 × 103 A W−1), and detectivity (1.99 × 1011 Jones). These improvements are attributed to impurity-assisted carrier excitation and more efficient charge transport. A band-modulation mechanism is proposed to account for the dual photoresponse observed in the doped devices. This study demonstrates that Bi doping is an effective approach for tuning carrier dynamics and optical absorption in InSe, providing a viable pathway toward high-performance 2D FETs and sensitive NIR photodetectors.