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.