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In atomically thin two-dimensional (2D) materials, free charges have quantized energy levels in one spatial dimension, while they are mobile in the other two.[1] The interest in such 2D materials increased in the late 1970s and early 1980s driven by a large amount of experimental outcomes from the development of molecular beam epitaxy (MBE) equipment for the deposition of high quality thin films of III-V semiconductors.[2] This resulted in the realization of high electron mobility transistors, with thin films of different bandgaps that can operate at very high frequencies. In such devices, the conduction band energy of at least one of the films is forced under the Fermi level at the junction, creating a narrow quantum well, and the quantization of free charges.[3] Such structures can offer electron mobilities larger than 10 6 cm 2 V− 1 s− 1 (at near zero Kelvin temperatures), which is significantly larger than that of silicon.[4] However, the high cost of the rare-earth materials, lack of compatibility, and technological difficulties for creating III-V structures hinders their widespread adaptation.

The emergence of graphene has revived the interest in 2D materials, due to its many favorable properties including enhanced electron mobilities that exceed 10 5 cm 2 V− 1 s− 1.[5] However, graphene lacks the semiconducting characteristics of prevalent materials, such as silicon with their natural energy bandgap.[5, 6] Even though there have been advancements in introducing a bandgap to graphene,[7] the required complex synthesis processes always resulted in significant loss in the much desired carrier mobilities.[8] It is suggested that alternative layered materials such …