CVD grown bilayer WSe2/MoSe2 heterostructures for high performance tunnel transistors

Bilayer WSe2/MoSe2 van der Waals heterostructures have been directly grown on SiO2/Si substrates by 2-step chemical vapor deposition method. Bilayer nature with well aligned in-plane crystal orientation has been confirmed by Raman and transmission electron microscopy characterizations. Back gate transistors having bilayer WSe2/MoSe2 in the source side have been fabricated and high on/off ratio larger than 106 have been obtained. Gate-induced modulation of electron direct tunneling from source metal to the bottom MoSe2 layer and band to band tunneling from the valence band of WSe2 to the conduction band of MoSe2 can be an operation mechanism. Thanks to the drastic reduction of contact resistance due to the change of electron injection configuration, from edge to area injection at the source electrode, much higher on/off ratio with steeper switching was obtained in the WSe2/MoSe2 bilayer device as compared with the monolayer MoSe2 and WSe2 devices.