A comparison of MoSe$_{2}$ field-effect transistors on SiO$_{2}$ and parylene-C substrates: possible surface polar phonon effects*

We report the fabrication and electrical characterization of high quality MoSe$_{2}$ field-effect transistors fabricated on both SiO$_{2}$ and parylene-C substrates. Multilayer MoSe$_{2}$ on parylene-C shows a significantly higher room temperature mobility of 100 cm$^{2}$V$^{-1}$s$^{-1} -$ 160 cm$^{2}$V$^{-1}$s$^{-1}$ than that on SiO$_{2}$ ($\approx $50 cm$^{2}$V$^{-1}$s$^{-1})$. Our variable temperature transport measurements indicate that the mobility of MoSe$_{2}$ devices on both SiO$_{2}$ and parylene-C increases to $\approx $ 500 cm$^{2}$V$^{-1}$s$^{-1}$ as the temperature decreases to below 100 K, with the mobility of MoSe$_{2}$ on SiO$_{2}$ increasing more rapidly. We attribute the observed difference in mobility and its temperature dependence between MoSe$_{2}$ on SiO$_{2}$ and on parylene-C primarily to the surface polar optical phonon scattering in the SiO$_{2}$ substrate, which is absent in parylene-C.