High optoelectronic performance of a local-back-gate ReS 2 /ReSe 2 heterojunction phototransistor with hafnium oxide dielectric.

A high optoelectronic performance ReS ₂ /ReSe ₂ van der Waals (vdW) heterojunction phototransistor utilizing thin hafnium oxide (HfO ₂ ) as a local-back-gate dielectric layer was prepared and studied. The heterojunction-based phototransistor exhibits a superior electrical performance with a large rectification ratio of ∼10 ³ . Furthermore, unlike diode-like heterojunction devices, the innovative introduction of a local-back-gate in this phototransistor provides an outstanding gate-tunable capability with an ultra-low off-state current of 433 fA and a high on/off current ratio of over 10 ⁶ . And under optical excitation of a wide spectrum from 400 to 633 nm, an excellent photodetection responsivity at the 10 ⁴ A W ^-1 level and the maximum normalized detectivity of 1.8 × 10 ¹⁵ Jones @ 633 nm have been demonstrated. Such high performances are attributed to the band alignment of the type-II heterojunction and the suppression of dark current by the local-back-gate. This work provides a promising reference for two-dimensional (2D) Re-based heterojunction optoelectronic devices.