Surface Segregation of the Composition in Gallium-Nitride Films

Resumo

The micro- and nanomorphology and local composition of gallium-nitride GaN films synthesized according to the metalorganic chemical-vapor deposition (MOCVD) technology are studied with the aim of detecting segregation phenomena. As a result, a complex picture of autosegregation is shown and discussed. In the main thick (~15 µm) gallium-nitride film, surface nonstoichiometry of the chemical composition (gallium deficiency) is revealed. The degree of nonstoichiometry (deviation of the relation at % Ga/at %N from unity) is ~0.20, whereas in the depth the deviation is less: from 0.02 to 0.10. At the same time in the thin (~1 µm) film, there is a significant excess of gallium up to individual nanocrystallites of metallic gallium. The mechanism of segregation which is presumably associated with the selective diffusion of nitrogen atoms or of gallium atoms to the surface and with the tendency of liquid gallium nanodroplets to coagulation is discussed.