Spectroscopic ellipsometry studies on the m-plane Al1%xInxN epilayers grown by metalorganic vapor phase epitaxy on a freestanding GaN substrate

Dispersion relationships of the refractive index and extinction coefficient of m-plane Al^1-xIn_xN epitaxial films (x = 0.00, 0.23, and 0.30) grown on a freestanding m-plane GaN substrate were determined by spectroscopic ellipsometry measurement. The experimentally obtained ellipsometric parameters tanψ and cosδ, which represent the differences in the p-and s-polarized amplitudes and phases of the incident light, respectively, were well fitted using the standard analytical functions. As the measurement was carried out at photon energies between 1.55 and 5.40 eV, the dispersion curves of the extinction coefficient k exhibited local maxima at approximately the Al_1-xIn_xN bandgap energies of x = 0.23 and 0.30, and the sample with x = 0.00 showed an ordinal absorption spectrum with a bandtail formed owing to high-concentration residual impurities. A large and x-dependent energy difference between the absorption and emission spectra (Stokes' shift) was observed for the Al_1-xIn_xN films, suggesting the presence of carrier localization phenomena.