Raman scattering properties of GaN thin films grown on sapphire under visible and ultraviolet excitation

Raman scattering properties from various GaN thin films grown on sapphire by metalorganic chemical vapor deposition were studied. Visible micro-Raman measurements show different mode behaviors with different laser incidence configurations. Raman lineshape analyses through two sets of equations led to the monitoring of the sample quality and stress and the optical determination of electrical properties of GaN films. An approximate 3 cm(-1) shift in the EI(LO) mode wavenumber is observed across the GaN film from the sapphire/GaN interface to the GaN surface, indicating the spatial variation of strains along the film growth direction within a few microns thickness range. Combined Raman and PL spectra were obtained under UV excitation, and interesting high-order resonance Raman features were observed using a sensitive UV-Raman-photoluminescence microscope. A new way to characterize p-type GaN is introduced. Copyright (C) 2001 John Wiley & Sons, Ltd.