Refractive index and birefringence of In x Ga 1– x N films grown by MOCVD

Abstract

The refractive index and birefringence of InxGa1–xN films grown on GaN layers were measured by prism coupling used in conjunction with multilayer optical waveguide analysis. Samples with x = 0.036, 0.049, 0.060, and 0.066 were examined at the separate wavelengths of 442, 457.9, 476.5, 488, 514.5, 532, and 632.8 nm. The In fraction x was determined by Rutherford backscattering spectroscopy. Separate measurements of the film thicknesses were performed by cross-sectional field-emission scanning electron microscopy (FESEM). Film thickness information was required in order to constrain the numerical simulation used to solve for the ordinary (no) and extraordinary (ne) refractive indices. We found that no is a weak function of both x and wavelength for the InGaN layers and could only be well distinguished from GaN (x = 0) for the two shortest wavelengths used. On the other hand, ne for the InGaN layers was resolved from GaN for all the wavelengths and x values. The measurements for ne are limited by optical scattering observed at the shortest wavelengths and the higher values of x. Cross-sectional FESEM reveals that a source of this scattering is most likely triangular pits at the InGaN/GaN upper interface. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)