Propagation of guided optical waves in thick GaN layers grown on (0001) sapphire

We report on the propagation of guided optical modes in insulating and Si-doped n-GaN layers grown by low-pressure metalorganic chemical vapor deposition (MOCVD) on (0001) sapphire substrates. The effective refractive indices of the guided modes were measured using the prism-coupling technique for layers with thicknesses from 1 to 6 μm. Ordinary and extraordinary refractive indices of GaN layers at wavelength of 632.8 nm were evaluated from the comparison of the measured index values and the index values calculated by solving the characteristic equation for a planar optical waveguide. The obtained results are in a good agreement with the step-like index profile model, indicating a high optical homogeneity of the investigated layers.