Dramatically enhanced ambient effects in a multi-layer MoS₂ transistor with channel thickness near maximum depletion width

It is known that semiconducting two-dimensional transition metal dichalcogenides such as MoS₂ and WSe₂, widely attracted as advanced field-effect transistors (FETs) due to good surface roughness in nano-scale and outstanding gate control with the desired bandgap, are significantly affected by oxygen and water molecules in air. Here, the channel thickness-dependent ambient effects on operation of multi-layer MoS₂ FETs are investigated for the first time. In particular, a multi-layer MoS₂ FET with channel thickness similar to the maximum depletion width (D_max) exhibited dramatic changes in the on-current to off-current (I_on/I_off) ratio under ambient conditions. The results were verified using numerical simulations. Our work is important in terms of the development and optimization of highly sensitive chemical or gas sensors, and it furthers our understanding of how multi-layer MoS₂ FETs operate.