Surface characterization of GaN and AlGaN layers grown by MOVPE

Surface properties of GaN and Al_0.17Ga_0.83N materials grown by metal organic vapor phase epitaxy (MOVPE) were systematically investigated by X-ray photoelectron spectroscopy (XPS). Air-exposed samples showed highly non-stoichiometric surfaces, which included a large amount of natural oxides. Deposition of Al on the air-exposed GaN surface caused interfacial reactions, resulting in the formation of oxide layers including Al₂O₃ and Ga oxide at the interface. A natural oxide layer of AlGaN surface possessed a complicated composition distribution in depth where the Al-oxide component was dominant on the topmost layer. Such natural oxide layers were found to be removed from GaN and AlGaN surfaces after the treatment in an NH₄OH solution at 50°C for 10 min, resulting in oxide-free and well-ordered surfaces.