Comparison of Electrical and Photoelectrical Properties of ReS 2 Field-Effect Transistors on Different Dielectric Substrates

As one of the newly discovered transition-metal dichalcogenides (TMDs), rhenium disulfide (ReS 2 ) has been investigated mostly because of its unique characteristics such as the direct band gap nature even in bulk form, which is not prominent in other TMDs (e.g., MoS 2, WSe 2, etc.). However, this material possesses a low mobility and an on/off ratio, which restrict its usage in high-speed and fast switching applications. Low mobilities or on/off ratios can also be caused by substrate scattering as well as environmental effects. In this study, we used few-layer ReS 2 (FL-ReS 2 ) as a channel material to investigate the substrate-dependent mobility, current on/off ratio, Schottky barrier height (SBH), and trap density of states of different dielectric substrates. The hexagonal boron nitride (h-BN)/FL-ReS 2 /h-BN structure was observed to exhibit a high mobility of 45 cm 2 V –1 s –1, current on/off ratio of about 10 7, the lowest SBH of about 12 mV at a zero back-gate voltage ( V bg ), and a low trap density of states of about 5 × 10 13 cm –3 . These quantities are reasonably superior compared to the FL-ReS 2 devices on SiO 2 substrates. We also observed a nearly 5-fold improvement in the photoresponsivity and external quantum efficiency values for the FL-ReS 2 devices on h-BN substrates. We believe that the photonic characteristics of TMDs can be improved by using h-BN as the substrate and capping layer.