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

Abstract

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 (ΔEC and ΔEV) 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 (ΔEC=3.98) and a better electrical stability than Gd2O3/ZnO (ΔEC=3.62) TFTs. The ZrZnO device achieves a threshold voltage (VTH) of −0.96V; the sub-threshold slope (S.S) is 0.21V/decade, the Ion/Ioff ratio is 2.46×106, and the field-effect mobility is 1.06cm2/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 αH=1.18×10−1 for the ZrZnO TFTs and αH=5.5×105 for the ZnO TFTs.