Spectroscopic ellipsometry studies of reactively sputtered nitrogen-rich GaAsN films

Nitrogen-rich GaAsN thin films have been deposited at 500 °C by reactive rf sputtering of GaAs target in argon-nitrogen atmosphere. The arsenic content of the films was varied by changing the nitrogen percentage in the sputtering atmosphere and the As/Ga ratio in the films was estimated by X-ray fluorescence measurements. Spectroscopic ellipsometry measurements have been carried out on these films and the measured ellispometric spectra were fitted with theoretical spectra generated by using suitable model sample structures. From the best fit parameters of the dispersion model, band-gap values and variation of refractive index and extinction coefficient as a function of wavelength have been obtained for films deposited with different percentages of nitrogen in the sputtering atmosphere. The films deposited with 12% to 100% nitrogen in the sputtering atmosphere, which are of hexagonal GaN, exhibit GaN-like optical properties, though effects due to excess arsenic in amorphous phase are seen in the films deposited with less than 40% nitrogen. The films deposited with 5% to 12% nitrogen in sputtering atmosphere are dominantly polycrystalline GaAs_xN_1−x (x ≈ 0.01 to 0.08) and exhibit variations in optical parameters, which are consistent with their structure and composition. The films deposited with less than 5% nitrogen in sputtering atmosphere are arsenic-rich and amorphous.