Abstract
We investigated the influence of low-concentration indium (In) doping on the chemical and structural properties of solution-processed zinc oxide (ZnO) films and the electrical characteristics of bottom-gate/top-contact In-doped ZnO thin-film transistors (TFTs). The thermogravimetry and differential scanning calorimetry analysis results showed that thermal annealing at 400 °C for 40 min produces In-doped ZnO films. As the In content of ZnO films was increased from 1% to 9%, the metal-oxygen bonding increased from 5.56% to 71.33%, while the metal-hydroxyl bonding decreased from 72.03% to 9.63%. The X-ray diffraction peaks and field-emission scanning microscope images of the ZnO films with different In concentrations revealed a better crystalline quality and reduced grain size of the solution-processed ZnO thin films. The thickness of the In-doped ZnO films also increased when the In content was increased up to 5%; however, the thickness decreased on further increasing the In content. The field-effect mobility and on/off current ratio of In-doped ZnO TFTs were notably affected by any change in the In concentration. Considering the overall TFT performance, the optimal In doping concentration in the solution-processed ZnO semiconductor was determined to be 5% in this study. These results suggest that low-concentration In incorporation is crucial for modulating the morphological characteristics of solution-processed ZnO thin films and the TFT performance.
Highlights
Zinc oxide (ZnO) has been extensively studied over the past few decades because it has a large direct band gap energy (3.4 eV), a high exciton binding energy (60 meV), resource availability, and nontoxicity [1,2]
Research is being carried out to improve the electrical characteristics of thin-film transistors (TFTs) fabricated with these oxide semiconductors, and pioneering work has been reported on oxide
These results demonstrate the successful fabrication of In-doped zinc oxide (ZnO) films with different In concentrations
Summary
Zinc oxide (ZnO) has been extensively studied over the past few decades because it has a large direct band gap energy (3.4 eV), a high exciton binding energy (60 meV), resource availability, and nontoxicity [1,2]. Reported a saturation mobility of 2–4 cm2 /Vs in ZnO TFTs processed via spin coating [11]. Note that grain boundaries in solution-processed ZnO semiconductor films can be a major constraint factor for the TFT performance because they act as trapping centers for mobile charge carriers. Rokn-Abadi et al reported better optical and electrical properties of the solution-processed ZnO film by doping it with 2%, 4%, 8% and 16% In concentrations [19]. These previous studies on In doping in solution-processed ZnO films focused mostly on the electrical, optical, and structural characteristics of the films. We investigated the effects of low-concentration In doping on the chemical and structural characteristics of solution-processed ZnO films. Impact of low-concentration In doping of solution-processed ZnO semiconductor films on the TFT performance
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