Linear- and nonlinear-optical properties of GaN thin films

Abstract

Results of a linear- and nonlinear-optical investigation of GaN thin films epitaxially deposited onto (0001)-oriented sapphire are reported. Wavelength- and angle-dependent linear transmission measurements were used to determine the thickness and the refractive index in the 500–1200-nm spectral region for a series of six GaN films. Analysis of angle-dependent, second-harmonic (SH) transmission profiles at 532 nm provided a quantitative evaluation of χxzx(2),χzxx(2), and χzzz(2) and a determination of the GaN lattice structure and tilt angle between the optical axis of the film and the surface normal of the sample. Dispersion effects between 500 nm and 1.064 μm prevented efficient SH production in individual GaN films that were greater than 2.5 μm in thickness. However, field calculations on a proposed multilayer GaN–sapphire structure observed a ninefold increase in the transmitted SH power as compared with a single GaN film.