Field Effect Transistors Using Atomically Thin Layers of Copper Indium Selenide (CuInSe)*

We will report fabrication of field-effect transistors (FETs) using few-layers of Copper Indium Selenide (CuInSe) flakes exfoliated from crystals grown using chemical vapor transport technique. Our transport measurements indicate n-type FET with electron mobility \textmu $\approx $ 3 cm$^{\mathrm{2}}$ V$^{\mathrm{-1}}$ s$^{\mathrm{-1}}$ at room temperature when Silicon dioxide (SiO$_{\mathrm{2}})$ is used as a back gate. Mobility can be further increased significantly when ionic liquid 1-Butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF$_{\mathrm{6}})$ is used as top gate. Similarly subthreshold swing can be further improved from 103 V/dec to 0.55 V/dec by using ionic liquid as a top gate. We also found ON/OFF ratio of $\approx $ 10$^{\mathrm{2}}$ for both top and back gate. Comparison between ionic liquid top gate and SiO$_{\mathrm{2}}$ back gate will be presented and discussed.