Thickness-dependent Electrical Conductivities in Transition Metal Dichalcogenides Layer Semiconductor Nanostructures
Ruei-San Chen (陳瑞山)1*, Chih-Che Tang (湯志哲)2, Wei-Chu Shen (沈韋竹)2, Ying-Sheng Huang (黃鶯聲)2
1Graduate Institute of Applied Science and Technology, National Taiwan University of Science and Technology, Taipei, Taiwan
2Department of Electronic Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan
* presenting author:陳瑞山,
We report on the observation of the substantial thickness (t)-dependent electrical conductivity (σ) at a wide thickness range for MoSe₂ layer semiconductor. The conductivity increases for over two orders of magnitude from 4.6 to 1500 Ω-1cm-1 with the decrease of thickness from 2700 to 6 nm. The conductivity was found to follow a nearly linear relationship with the reciprocal thickness, i.e. σ ∝ 1/t. The temperature-dependent conductivity measurements also show that the MoSe₂ multilayers with much lower activation energies at 3.5-8.5 meV than those (36-38 meV) of the bulks, indicating the different origins of majority carrier. Similar thickness-dependent transport properties can also be reproduced and observed in the other transition metal dichalcogenide (TMD) layer semiconductors such as MoS₂ and WS₂. These results imply the presence of higher surface conductivity or electron surface accumulation in these layer crystals. In addition, the fabrication of ohmic contacts for the MoSe₂ layer nanocrystals by focused-ion beam (FIB) technique was also demonstrated.

Keywords: molybdenum diselenide, layer semiconductor, conductivity, ohmic contact, transition metal dichalcogenide