Effects of Nitrogen Flow Ratio on the Properties of Radiofrequency-Sputtered InGaN Films

Indium gallium nitride (InGaN) thin films have been prepared on quartz glass substrates at various nitrogen flow ratios by radiofrequency (rf) reactive magnetron sputtering. At lower nitrogen flow ratio of 30%, the as-grown InGaN film exhibits an amorphous structure. As the nitrogen flow ratio increases from 40% to 60%, grazing-incidence x-ray diffraction (GIXRD) peaks corresponding to wurtzite InGaN are observed. At higher nitrogen flow ratios of 80% and 100%, the films exhibit highly oriented fine columnar structure and the texture of the wurtzite structure changes from (0002) to (). The nitrogen flow ratio has a significant effect on the crystalline orientation and the intensity of the peak signals. A redshift of the absorption edge occurs, and the bandgap E (g) tends to decrease with increasing nitrogen flow ratio. The sheet resistance R (s) and the resistivity rho of the InGaN films decrease due to the contribution of the comparatively narrow intercrystalline barriers. All the InGaN films have low mobility values, and show n-type conductivity with carrier concentration depending on the nitrogen flow ratio.