High-performance heterojunctions based on 2D semiconductors

Electronic devices based on atomic layered two-dimensional materials have recently attracted great research attention due to their unique electronic properties and the feasibility of hybrid integration which provides the unprecedented opportunities for various van der Waals heterojunctions. The fact that the formation of heterojunctions can be achieved by simple dry transfer has eliminated the necessity of high-temperature and high vacuum process required for traditional heterojunction growth which also needs to consider lattice constant and thermal expansion coefficient mismatch. Transitional metal dichalcogenides such as molybdenum disulfide is typically an n-type material with a bandgap of around 1.7 eV. Elemental layered black phosphorus has been discovered to be p-type doped with a bandgap of around 0.3 eV for film thickness above 10 nm. The combination of these two materials enables the possibility to form both vertical and lateral p-n heterojunctions where the Fermi level and band alignment can be modulated by the gate voltage and drain voltage. As an example, vertical heterojunction based on the above two materials exhibits both diode and transistor behavior with ultrahigh rectification ratio and on-off ratio simultaneously. Lateral heterojunctions, on the other hand, exhibit unique negative transconductance and thus will result in non-traditional ternary inverters whose transition from the conventional binary CMOS inverter can be realized by the band profile alignment from drain bias.