Structural and optical characterization of AlGaN/GaN layers

Abstract

High quality AlxGa1−xN layers have been grown on c-plane sapphire substrate by Metal Organic Vapor Phase Epitaxy. The aluminum (Al) composition was varied from 15% to 51%. When the flow rate of trimethylaluminum was increased, the growth rate was found to be decreased. The crystalline quality of AlGaN layers has been evaluated using High Resolution X-ray Diffraction rocking curves. Reciprocal Space Mapping results confirmed that at low Al composition (x=0.15), AlGaN layers are found to be fully strained. At high Al composition (x=0.33, 0.51), AlGaN layers are relaxed by generation of cracks due to lattice mismatch. The optical properties of AlGaN/GaN layers have been investigated by room temperature photoluminescence. With increasing Al content, the AlGaN emission peak has been found to shift towards higher energies. The surface morphology and roughness of AlGaN have been studied by Atomic Force Microscopy. Root Mean Square roughness values have been found to increase with the increase of Al.