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

Abstract

The surface stoichiometry of GaN grown by metal-organic vapor-phase epitaxy (MOVPE) on (0001) sapphire substrate at temperatures up to about 1000°C in N2 and H2 carrier gases was monitored in situ by surface photoabsorption (SPA). In the N2 carrier gas with NH3 supply, a stable N-rich surface was formed at temperatures up to 1030°C. In contrast, the surface in H2 carrier gas was N-rich at temperatures below 850–900°C. Above these temperatures the surface became Ga-rich. These results indicate that GaN MOVPE growth at temperatures around 1000°C proceeds under N-rich and Ga-rich surface stoichiometry in N2 and H2, respectively. The N desorption rate in N2 was lower than the rate in H2, indicating that the N2 carrier gas suppresses the N desorption from the GaN MOVPE surface compared with H2.