Spectroscopic ellipsometry characterization of amorphous aluminum nitride and indium nitride thin films

We have measured and analyzed the optical characteristics of a series of amorphous aluminum nitride, a-AIN, End amorphous indium nitride, a-InN, thin films deposited on crystalline silicon, c-Si (111), by RF reactive magnetron sputtering at temperature T < 325 K. Spectroscopic Ellipsometry measurements were carried out at two angles of incidence, 70 degrees and 75 degrees, over the wavelength range 300-1400 nm. The measured ellipsometric data were fitted to models consisting of air / a-AIN/Sio(2) / c-Si (111) and air / roughness / a-InN/ Sio(2)/ c-Si (111). The roughness was modeled using the Bruggeman effective medium approximation, assuming 50% a-InN and 50% voids. The optical constants and the thicknesses of amorphous (Al, In) N films were obtained by the analysis of the measured ellipsometric spectra through the Cauchy-Urbach and the Tauc-Lorentz models, respectively. X-ray diffraction (XRD) analysis confirmed the amorphous nature of the films under study.