Effect of fluctuation in Al incorporation on the microstructure, bond lengths, and surface properties of an Al x Ga1−x N epitaxial layer

Abstract

Al x Ga1−x N (0.15 ≤ x ≤ 0.87) epilayers were grown on sapphire substrates by metal-organic chemical vapor deposition (MOCVD). The lattice deformation, chemical bonding states, and local electronic structure were characterized by a series of techniques, including X-ray diffraction (XRD), Raman scattering, X-ray photoelectron (XPS), and extended Xray absorption fine structure (EXAFS) spectroscopy. The XRD and Raman spectra revealed that substitution of Ga with Al in Al x Ga1−x N epilayers induces a significant contraction in the crystal lattice and a slight expansion of internal parameter u. The XPS measurements indicated the absence of remarkable disorder of the chemical bonds in AlGaN with a high Al content. The EXAFS analysis also demonstrated that the Ga-N and Ga-Al bond lengths are independent of the Al content, whereas the Ga-Ga bond length varies with Al content.