Enhanced photoresponsivity and hole mobility of MoTe₂ phototransistors by using an Al₂O₃ high-κ gate dielectric

Molybdenum ditelluride (MoTe₂) has been demonstrated great potential in electronic and optoelectronic applications. However, the reported effective hole mobility remains far below its theoretical value. Herein, taking advantage of high-κ screening effect, we have fabricated back-gated MoTe₂ transistors on an Al₂O₃ high-κ dielectric and systematically investigated the electronic and optoelectronic properties. A high current on/off ratio exceeding 10⁶ is achieved in the Al₂O₃-based MoTe₂ transistors, and the hole mobility is demonstrated to be 150 cm² V⁻¹ s⁻¹, compared to 0.2–20 cm² V⁻¹ s⁻¹ ever obtained from back-gated MoTe₂ transistors in the literatures. Moreover, a considerable hole concentration of 1.2 × 10¹³ cm⁻² is attained in our Al₂O₃-based MoTe₂ transistors owing to the strong gate control capability, leading to a high on-state hole current of 6.1 μA μm⁻¹. After optimization, our Al₂O₃-based MoTe₂ phototransistor exhibits outstanding photodetective performance, with a high responsivity of 543 A W⁻¹ and a high photogain of 1,662 at 405 nm light illumination, which are boosted around 419 times compared to the referential SiO₂-based control devices. The mechanisms of photoconductivity in the Al₂O₃-based MoTe₂ phototransistors have been analyzed in detail, and the photogating effect is considered to play an important role. This work may provide useful insight to improve carrier mobility in two-dimensional layered semiconductors and open opportunities to facilitate the development of high-performance photodetectors in the future.