Insulator-to-metal transition in ZnO by electric double layer gating

The authors report high-density carrier accumulation and a gate-induced insulator-to-metal transition in ZnO single-crystalline thin-film field effect transistors by adopting electric double layers as gate dielectrics. Hall effect measurements showed that a sheet carrier density of 4.2x10(13) cm(-2) was achieved. The highest sheet conductance at room temperature was similar to 1 mS, which was sufficient to maintain the metallic state down to 10 K. These results strongly suggest the versatility of electric double layer gating for various materials.