Atomic layer deposition of Nb-doped ZnO for thin film transistors

摘要

We present physical and electrical characterization of niobium-doped zinc oxide (NbZnO) for thin film transistor (TFT) applications. The NbZnO films were deposited using atomic layer deposition. X-ray diffraction measurements indicate that the crystallinity of the NbZnO films reduces with an increase in the Nb content and lower deposition temperature. It was confirmed using X-ray photo-electron spectroscopy that Nb~(5+) is present within the NbZnO matrix. Furthermore, photolumines-cence indicates that the band gap of the ZnO increases with a higher Nb content, which is explained by the Burstein-Moss effect. For TFT applications, a growth temperature of 175 ℃ for 3.8% NbZnO provided the best TFT characteristics with a saturation mobility of 7.9cm~2/Vs, the current On/Off ratio of 1 × 10~8, and the subthreshold swing of 0.34 V/decade. The transport is seen to follow a multiple-trap and release mechanism at lower gate voltages and percolation thereafter.