Optical investigations and strain effect in AlGaN/GaN epitaxial layers

AlxGa1-xN epilayers with x ranging from 0.20 to 0.50 have been grown on c-plane sapphire substrate by metal-organic chemical vapor deposition. The thickness, composition, strain and stress values of the AlGaN were determined by high resolution X-ray diffraction. The optical properties of the epilayers were studied using photoluminescence (PL) and reflectivity measurements. The effect of the stress on the bandgap can be explained by room temperature PL. The temperature dependent PL result shows the well-known "S-shape" behavior.