Hall and field-effect mobilities in few layered $p$-WSe$_2$ field-effect transistors

Abstract: Here, we present a temperature ($T$) dependent comparison between field-effect and Hall mobilities in field-effect transistors based on few-layered WSe$_2$ exfoliated onto SiO$_2$. Without dielectric engineering and beyond a $T$-dependent threshold gate-voltage, we observe maximum hole mobilities approaching 350 cm$^2$/Vs at $T$=300 K. The hole Hall mobility reaches a maximum value of 650 cm$^2$/Vs as $T$ is lowered below $\sim$ 150 K, indicating that insofar WSe$_2$-based field-effect transistors (FETs) display the largest Hall mobilities among the transition metal dichalcogenides. The gate capacitance, as extracted from the Hall-effect, reveals the presence of spurious charges in the channel, while the two-terminal sheet resistivity displays two-dimensional variable-range hopping behavior, indicating carrier localization induced by disorder at the interface between WSe$_2$ and SiO$_2$. We argue that improvements in the fabrication protocols as, for example, the use of a substrate free of dangling bonds are likely to produce WSe$_2$-based FETs displaying higher room temperature mobilities, i.e. approaching those of $p$-doped Si, which would make it a suitable candidate for high performance opto-electronics.