Charge injection mechanism from contact electrodes into two-dimensional (2D) dichalcogenides is an essential topic for exploiting electronics based on 2D channels, but remains not well understood. Here, low-work-function metal ytterbium (Yb) was employed as contacts for tungsten disulfide (WS2) to understand the realistic injection mechanism. The contact properties in WS2 with variable temperature (T) and channel thickness (tch) were synergetically characterized. It is found that the Yb/WS2 interfaces exhibit a strong pinning effect between energy levels and a low contact resistance (R_\rm{C}) value down to 5kΩ⋅μm. Cryogenic electrical measurements reveal that R_\rm{C} exhibits weakly positive dependence on T till 77 K, as well as a weakly negative correlation with tch. In contrast to the non-negligible R_\rm{C} values extracted, an unexpectedly low effective thermal injection barrier of 36 meV is estimated, indicating the presence of significant tunneling injection in subthreshold regime and the inapplicability of the pure thermionic emission model to estimate the height of injection barrier.
@article{arxiv.2306.15689,
title = {Electrical contact properties between Yb and few-layer WS$_2$},
author = {Shihao Ju and Lipeng Qiu and Jian Zhou and Binxi Liang and Wenfeng Wang and Taotao Li and Jian Chen and Xinran Wang and Yi Shi and Songlin Li},
journal= {arXiv preprint arXiv:2306.15689},
year = {2023}
}