Initial growth stages of cubic GaN (c-GaN) films on GaAs(0 0 1) in low-pressure MOVPE were studied by spectroscopic ellipsometry. The GaN buffer layer was deposited at 500°C and was then annealed at 700°C with H2/monomethylhydrazine (MMHy) ambient. Spectroscopic ellipsometry revealed that the buffer layer thickness was increased and the surface was roughened during the annealing process. The change of surface morphology was also confirmed by the atomic force microscopy measurement. These observations would be associated with the nitridation of the GaAs substrate by the ambient MMHy and re-crystallization of the GaN buffer layer. Spectroscopic ellipsometry is a helpful technique to study the initial growth stages of GaN films on GaAs substrates.
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