Optical anisotropy of a-plane Al0.8In0.2N grown on an a-plane GaN pseudosubstrate

The optical properties of a-plane Al_1−xIn_xN grown by metal-organic vapor phase epitaxy on an a-plane GaN/r-plane sapphire template are reported. X-ray diffraction yielded an In content of ∼20%. The ordinary and extraordinary dielectric functions (DFs) were obtained by spectroscopic ellipsometry in the spectral range from 1 eV up to 6 eV at room temperature. By fitting the experimentally obtained complex DF, the inter-band transitions E_A and E_B, which are allowed for configurations  and , respectively, were determined. A redshift of ∼200 meV is found for the transition E_B with respect to transition E_A attributed to the optical selection rules. Furthermore, the ordinary and extraordinary refractive indices in the transparent region (below the band gap) are represented in the analytical form. The AlInN alloy shows the positive birefringence and the difference between the extraordinary and ordinary refractive index n_e − n_o is defined to be 0.068 at photon energy of 3 eV. Finally, the ordinary and extraordinary high-energy dielectric constants were estimated.