Band offsets and electrical stability characterization of Zr-doped ZnO thin-film transistors with a Gd2O3 gate insulator

The performance of zirconium (Zr) doped zinc oxide (ZnO) thin-film transistors (TFTs) grown using an RF co-sputtering method is investigated. This study determines the properties of ZrZnO channel and ZnO channel TFT devices using reactively evaporated Gd2O3 as a gate dielectric. The energy discontinuity in the band offsets (Delta E-C and Delta E-V) of the Gd2O3/ZrZnO and Gd2O3/ZnO heterostructures is measured using X-ray photoelectron spectroscopy (XPS). The Gd2O3/ZrZnO TFTs exhibit a better conduction band offset (Delta E-C = 3.98) and a better electrical stability than Gd2O3/ZnO (Delta E-C = 3.62) TFTs. The ZrZnO device achieves a threshold voltage (V-TH) of -0.96 V; the sub-threshold slope (S.S) is 0.21 V/decade, the I-on/l(off) ratio is 2.46 x 106, and the field-effect mobility is 1.06 cm(2)/V-s. In addition, the low-frequency noise (LFN) behavior of ZrZnO and ZnO thin-film transistors is also observed. The fluctuation caused by trapping/ detrapping can be reduced by the Zr dopants of the TFT devices. The Hooge's parameters are determined to be alpha(H) = 1.18 x 10(-1) for the ZrZnO TFTs and alpha(H) = 5.5 x 10(5) for the ZnO TFTs. (C) 2014 Elsevier B.V. All rights reserved.