A facile solution-doping method to improve a low-temperature zinc oxide precursor : Towards low-cost electronics on plastic foil

Optimization of thin-film transistors performance is usually accompanied by an increase of the process temperature. This work presents a method to raise the field effect mobility by a factor of 3 without a change of the process parameters. The modification involves a solution doping process where an ammine zinc complex is formed in the presence of metal ions of the 13th group, namely gallium and indium. Morphological studies, including scanning electron microscopy and atomic force microscopy, reveal the difference among the resulting films. Moreover, X-ray diffraction results show that the doping affects the preferred orientation of the zinc oxide crystals in the resulting film. The electrical properties vary distinctly and are best for a solution doped with both gallium and indium. With a double-layer system the performance of this new precursor exceeds field effect mobility values of 1 cm2 V-1 s-1 after a maximum process temperature of 160 °C. The performance of ZnO-based field-effect transistors is improved by a simple solution-doping procedure using ions of the 13th group. The method has a strong influence on the film morphology and orientation of the crystallites. This leads to field effect mobility values comparable to amorphous silicon. The low conversion temperature allows the fabrication on flexible substrates.