Surface morphology engineering of metal oxide-transition metal dichalcogenide heterojunction

A tremendous effort has been made to develop 2D materials-based FETs for electronic applications due to their atomically thin structures. Typically, the electrical performance of the device can vary with the surface roughness and thickness of the channel layer. Therefore, a two-step surface engineering process is demonstrated to tailor the surface roughness and thickness of MoSe₂ multilayers involving exposure of O₂ plasma followed by dipping in (NH₄)₂S(aq) solution. The O₂ plasma treatment generated an amorphous MoO_x layer to form a MoO_x/MoSe₂ heterojunction, and the (NH₄)₂S(aq) treatment tailored the surface roughness of the heterojunction. The ON/OFF current ratio of MoSe₂ FET is about 1.1 × 10⁵ and 5.7 × 10⁴ for bare and chemically etched MoSe₂, respectively. The surface roughness of the chemically treated MoSe₂ is higher than that of the bare, 4.2 ± 0.5 nm against 3.6 ± 0.5 nm. Conversely, a 1-hour exposure of the multilayer MoO_x/MoSe₂ heterostructure with the (NH₄)₂S(aq) solution removed the amorphous oxide layer and scaled down the thickness of MoSe₂ from ~92.2 nm to ~38.9 nm. The preliminary study shows that this simple two-step strategy can obtain a higher surface-area-to-volume ratio and thickness engineering with acceptable variation in electrical properties.