Influence of N2 carrier gas on surface stoichiometry in GaN MOVPE studied by surface photoabsorption

The surface stoichiometry of GaN grown by metal-organic vapor-phase epitaxy (MOVPE) on (0 0 0 1) sapphire substrate at temperatures up to about 1000 degrees C in N-2 and H-2 carrier gases was monitored in situ by surface photoabsorption (SPA). In the N-2 carrier gas with NH3 supply, a stable N-rich surface was formed at temperatures up to 1030 degrees C. In contrast, the surface in H-2 carrier gas was N-rich at temperatures below 850-900 degrees C. Above these temperatures the surface became Ga-rich. These results indicate that GaN MOVPE growth at temperatures around 1000 degrees C proceeds under N-rich and Ga-rich surface stoichiometry in N-2 and H-2, respectively, The N desorption rate in N-2 was lower than the rate in H-2, indicating that the N-2 carrier gas suppresses the N desorption from the GaN MOVPE surface compared with H-2. (C) 1998 Elsevier Science B.V. All rights reserved.