The correlation of material properties and deposition condition of ZnON thin films

Amorphous and nanocrystalline Zinc Oxynitride (nc-ZnON) has been found to be one kind of potential materials for thin film transistors in the application of advanced display because of their high carrier mobility and low persistent photocurrent. We report a systematic study of ZnON properties and their correlation to the deposition conditions in a reactive sputtering process using a metallic Zn target in a gas mixture of Ar, N2 and O2. The most sensitive parameter to the material properties is O2 and N2 flow rates. At given N2 and Ar flow rates, the ZnON materials show polycrystalline ZnO properties when a relatively high O2 flow rate is used; become a mixture of ZnO and Zn3N2 with a nanocrystalline structure when a medium O2 flow rate is used; and finally show polycrystalline Zn3N2 properties when a small or no O2 flow rate is used. The RF power also shows a strong influence on the material properties. At a given gas mixture, a low RF power produces polycrystalline ZnO-like materials and a high power produces polycrystalline Zn3N2-like materials. At an optimized medium RF power, the material shows nc-ZnON properties. Finally, under the optimized condition, the nc-ZnON films are made with an optical bandgap of 1.3-1.5 eV, electron mobility above 80 cm2/V.s and electron density of 1x1018 cm-3, which are suitable for high quality TFTs in advanced display application.