Crossover between Thermo- and Field-assisted Carrier Injection in Staggered pn Heterojunction of MoTe2 and ReS2

Abstract In semiconductor devices, understanding and controlling the properties of metal-semiconductor and semiconductor-semiconductor junctions is vital. A wide variety of heterojunctions using transition metal dichalcogenides (TMDs) have been fabricated and characterized. Rectification of the drain-source current (Ids) has been observed from p/n-TMD junctions, which is responsible for thermionic emission. In this study, we investigated diode behaviors of MoTe2 and ReS2 heterostructures, whose built-in potential ranged between 0.18 and 0.37 eV; however, we observed that the device showed a crossover between thermionic and Fowler-Nordheim (F-N) tunneling for a carrier injection mechanism. Thermionic emission existed within a narrow temperature and bias windows. Our experimental and theoretical analyses revealed that the carrier injection can be controlled by modulating the potential barrier height, temperature, and applied strength. For instance, at 300 K under a low drain-source voltage Vds, the carriers were thermally injected. Subsequently, the injection mechanism quickly shifted to the thermal field and F-N tunneling as Vds increased. Furthermore, when the temperature was lower than 220 K, the field-enhanced tunneling of the carrier prevailed regardless of Vds magnitude. This result expands the insight into the charge transport mechanism in staggered TMD heterojunctions.