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 reflectome try, was found to be dependent on the substrate temperature and the flow ra te 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 v arious temperatures in H-2. Two regimes are clearly identified; below 830 d egrees C with an activation energy of 1.87 eV and over 830 degrees C with a n activation energy of 0.38 eV. Finally, results are analysed using thermod ynamic calculation based on the minimisation of the Gibbs energy of the sys tem. (C) 1999 Elsevier Science B.V. All rights reserved.