An XPS study of the effect of nitrogen exposure time and temperature on the GaAs(001) surface using atomic nitrogen

The effect of atomic nitrogen, generated by a radio frequency plasma source, on clean GaAs(001) surfaces, has been examined using X-ray photoemission spectroscopy (XPS). The GaAs substrates were cleaned in a molecular-beam epitaxy style growth chamber using atomic hydrogen with the sample held at 400°C. The ‘nitridation’ of the surface was performed under fixed plasma conditions, compatible with the molecular beam epitaxial growth on GaN, and as a function of both time (up to 45 min) and temperature (in the range ∼ 300–620°C). Curve fitting of the XPS spectra, to reveal the nature of the reaction products, showed a chemically shifted Ga 3d core level peak corresponding to the formation of GaN on GaAs. The rate of the nitridation reaction was found to decrease with nitrogen exposure time and became effectively zero at the low temperatures (300 and 450°C) after approximately 20 min. The rate of the reaction increased with sample temperature and was very aggressive above 600°C, readily forming thicker GaN films of a polycrystalline nature.