In situ optical monitoring of the decomposition of GaN thin films

The GaN thermal decomposition versus the annealing ambient (H-2, N-2 + H-2, H-2 + NH3), is investigated in an atmospheric pressure metalorganic vapour phase reactor. The GaN decomposition rate, measured using laser reflectometry, was found to be dependent on the substrate temperature and the flow rate of H-2. A high thermal unstability of GaN in the presence of H-2 gas at 1050 degrees C, is shown. The introduction of nitrogen N-2 blocks partially the decomposition of GaN. Also, we investigated the GaN decomposition at various temperatures in H-2. Two regimes are clearly identified; below 830 degrees C with an activation energy of 1.87 eV and over 830 degrees C with an activation energy of 0.38 eV. Finally, results are analysed using thermodynamic calculation based on the minimisation of the Gibbs energy of the system. (C) 1999 Elsevier Science B.V. All rights reserved.