Optical characterization of sputtered amorphous aluminum nitride thin films by spectroscopic ellipsometry

• Published in: Journal of non-crystalline solids Vol. 351; no. 40-42; pp. 3334 - 3340
• Main Authors: Khoshman, Jebreel M., Kordesch, Martin E.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.10.2005; Elsevier
• Subjects: Amorphous semiconductors; glasses; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of specific thin films; Physics; 78.20.−e; A1955; E280; O110; E260; T200; 78.20.Ci; Spectroscopic ellipsometry; Refractive index; 78.20.-e; Amorphous state; Absorption coefficients; Extinction index; Thin films; Reflectivity; Cathode sputtering; Energy gap; Aluminium nitrides; Reactive sputtering; Urbach rule; Optical constants; Radiofrequency sputtering
• ISSN: 0022-3093; 1873-4812
• DOI: 10.1016/j.jnoncrysol.2005.08.009

We have measured and analyzed the optical constants and polarized optical properties of amorphous aluminum nitride (a-AlN) thin films deposited by RF reactive magnetron sputtering onto silicon(111) and glass substrates. The optical constants were obtained by analysis of the measured ellipsometric spectra in the wavelength range 300–1400nm, using the Cauchy–Urbach model. Refractive indices and extinction coefficients of the films were determined to be in the range 1.80–2.11 and 8.6×10−3–1.5×10−5, respectively. Analysis of the absorption coefficient, in the wavelength range 200–1400nm, shows the bandgap of a-AlN thin films to be 5.84±0.05eV. From the angle dependence of the p-polarized reflectivity we deduce a Brewster angle of 61° and a principal angle of 64°. Measurement of the polarized optical properties reveals a high transmissivity and very low absorptivity for a-AlN films in the visible and near infrared regions. X-ray diffraction analysis confirmed the amorphous nature of the films under study.