Screening limited switching performance of multilayer 2D semiconductor FETs: the case for SnS

Multilayer tin mono-sulfide (SnS) field-effect transistor (FET) devices with thickness between 50 to 100 nm with gate tunable p-type carriers were fabricated and studied. The fabricated devices demonstrated anisotropic inplane conductance and room temperature field effect mobility ranging from 5 to 10 cm$^{\mathrm{2}}$/Vs. However, weak gate tuning was shown to underestimate the field effect mobility. The finite screening length effect was demonstrated to be the cause of appreciable OFF state conductance, ON-OFF ratio of 10 at room temperature and the weak gate tuning. Etching and n-type surface doping by Cs$_{\mathrm{2}}$CO$_{\mathrm{3}}$ to reduce non-gatable holes near the sample's top surface were perform and the devices showed an order of magnitude improvement in the ON-OFF ratio and hole Hall mobility \textasciitilde 100 cm$^{\mathrm{2}}$/Vs at room temperature is observed. This demonstrates that in order to obtain strong gate effect and switching on 2D semiconductor, the samples thickness must lie within the regime of Debye screening length. Work's online publication:~DOI: 10.1039/C6NR07098A.~\underline {\textbf{arXiv:1608.06501}}