Ambipolar transistor action of germanane electric double layer transistor

Abstract

Germanane (GeH) is a hydrogen-terminated layered crystal of germanium. We fabricated an electric double layer transistor (EDLT) on a GeH thin film on the Ge (111) substrate and investigated its electronic properties. The EDLT showed ambipolar transfer characteristics at 240 K. The sheet resistance Rsheet at null gate bias (VG = 0 V) exceeded 1 MΩ below 100 K, which indicates an insulating behavior. For VG = −2 V (hole accumulation), a gradual increase in Rsheet up to 10 kΩ was found upon decreasing temperature to 40 K, i.e., semiconducting or even weakly insulating. Remarkably, Rsheet for VG = 1 V (electron accumulation) decreased down to 3 kΩ upon decreasing temperature to 40 K, indicating metallic conduction. Accumulation of electrons (holes) was confirmed for VG > 1 V (VG < −1 V) by Hall effect measurements. Hall mobilities of electrons and holes, which increase with decreasing temperature, were 6500 cm2 V−1 s−1 and 570 cm2 V−1 s−1, respectively, at 120 K.