Morphology and Optical Properties of RF Sputtering Deposited Indium Nitride Layers Under Different N₂/Ar Ratio

InN thin films were prepared using reactive radio frequency sputtering on (111) Si substrates under different N₂/Ar ratio. The surface morphology and optical properties of InN thin films were characterized by X-ray diffraction, atomic force microscopy, scanning electron microscope, energy dispersive spectrometer, and UV-visible-NIR spectrophotometer at room temperature. It was found that the growth rate and surface RMS roughness of InN layers all significantly decreased with the increasing of N₂ content in the sputtering gas. All the InN films were wurtzite structure with the proportion of N₂ increasing from 40% to 100% in the mixture gas. The highly c-axis orientation InN films could only be obtained in the composition ratios of N₂ higher than 90%. The atomic percentage of N is much higher than that of In at high N₂ content films, which mainly due to the chemical reaction on the surface of Si substrate. The apparent optical band gap energy is estimated at 1.83 eV. However, the InN absorption band tail is strongly influenced by the sputtering due to a change in the species of the plasma.