In situ Raman monitoring of the molecular beam epitaxial growth of gallium nitride

Raman spectroscopy was applied to monitor the growth of GaN st temperatures around 600 degrees C without interrupting the growth process. GaN was deposited on GaAs(100) and Si(111) substrates by molecular beam epitaxy using elemental Ga and atomic nitrogen provided by an r.f. plasma source. Sufficient signal-to-noise ratio in the spectra was achieved by carefully choosing the excitation photon energy in the vicinity of the bandgap at the elevated temperature and thus realizing conditions for resonant Raman scattering. Owing to the difference in bandgap energy of 0.2 eV between the distinct modifications of GaN, the resonance condition also leads to a selective enhancement of the scattering cross-section of either the cubic or the hexagonal phase. (C) 1997 John Wiley & Sons, Ltd.