Field-Effect Transistors Based on Few-Layered Ambipolar MoSe$_{2}$ and $\alpha $-MoTe$_{2}$*

We report a room temperature study on the electrical responses of field-effect transistors (FETs) based on few-layered MoSe$_{2}$ and MoTe$_{2}$, grown by chemical vapor transport, mechanically exfoliated onto SiO$_{2}$. MoSe$_{2}$ FETs electrically contacted with Ti display ambipolar behavior with current on/off ratios up to 10$^{6}$ for both hole and electron channels. For both channels the Hall effect indicates Hall mobilities $\mu_{\mathrm{H}} \quad \simeq $ 250 cm$^{2}$/(Vs), which are comparable to the corresponding field-effect mobilities, $\mu_{\mathrm{FE}} \quad \sim $ 175 cm$^{2}$/(Vs), evaluated through two-terminal field-effect configuration. MoTe$_{2}$ field-effect transistors are observed to be hole-doped, displaying on/off ratios of $\sim$ 10$^{6}$ and subthreshold swings of $\sim $140 mV per decade. Our results suggest that MoSe$_{2}$ is a good candidate for single atomic layer p$-$n junctions and for low-power, complementary logic applications, with MoTe$_{2}$ having similar properties. However, in MoTe$_{2}$ we observe a field-effect mobility of only $\mu_{\mathrm{FE}} \quad \sim $ 20 cm$^{2}$/(Vs) in a bilayer device and $\sim$ 27 cm$^{2}$/(Vs) in seven layers.