FETs based on wide bandgap oxides such as β-Ga 2O 3 (bandgap of 4.8 eV 20 I on/ I off ratio of ~10 7–10 9 and electron mobility of 32–180 cm 2V −1s −1 21) and In 2O 3 (bandgap of 3.1 eV 22 I on/ I off ratio of ~10 6 and electron mobility of 127 cm 2V −1s −1 23) provide excellent I on/ I off ratios but the carrier mobilities are low.

However, understanding of the carrier transport and realization of large-area growth are challenges that limit applications 18, 19. In addition, such heterostructures provide high I on/ I off ratios of ~10 3 for WSe 2–MoS 2 and MoTe 2–SnSe 2 14, ~10 4 for MoS 2–CuInP 2S 6 15, ~10 6 for MoTe 2–SnS 2 16, and ~10 7 for WS 2-graphene 17. Stacking of transition metal dichalcogenides in van der Waals heterostructures can improve the carrier mobility 13. Monolayer transition metal dichalcogenides possess (direct) bandgaps of 1–2 eV 6, 7, 8, 9 and provide high I on/ I off ratios of ~10 5–10 8 10, 11, while low carrier mobilities of ~10 2 cm 2V −1s −1 12 are not appropriate for high performance applications. Despite an ultrahigh carrier mobility of ~10 5 cm 2V −1s −1, graphene cannot be used as channel material due to its zero bandgap nature. Two-dimensional materials currently receive immense attention for application in next-generation electronic devices, particularly as channel materials in field effect transistors (FETs) 1, 2, 3, 4, 5.

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