A study of variable range hopping conduction of a sol-gel ZnSnO thin film transistor using low temperature measurements

Abstract

This paper investigates variable range hopping conduction of a zinc tin oxide (ZTO) thin-film transistor (TFT). The ZTO channel layer was fabricated using a sol-gel process. Existence of Zn2SnO4 and ZnSnO3 crystal phases in the ZTO film is observed in the X-ray diffraction pattern. Distinct lattice fringes with different orientations that are observed in the transmission electron microscopy image verify the polycrystalline structure of the ZTO layer. To study the hopping mechanism, electrical characteristics of the ZTO TFT were measured at low temperatures of 100–220 K. The activation energy (Ea) is 97 meV when the gate voltage is 0 V, and it exponentially decreases with increasing gate voltage. The Ea is 22 meV when the gate voltage increases to 30 V. A negative exponential relationship between the density of states and the Ea is found. Temperature and gate voltage dependence of the hopping distance and hopping energy are also explored.