Kinetics of tin segregation on crystalline semiconductor surfaces: effect of the defects induced by ion bombardment

Sn surface segregation kinetics from (111) and (123) Ge(Sn) single crystalline solid solutions were studied by AES experiments. One observes (i) a great influence of the surface orientation on the phenomenon (ii) a very high value of the Sn diffusion coefficients which do not present an Arrhenius behaviour linked to bulk diffusion of tin in germanium. The results are analysed taking into account the effect of the ion sputtering performed to clean the surface before segregation studies. If the main interaction term responsible for tin surface segregation is Sn–Sn attraction as in metallic alloys, ion bombardment amorphizes the bulk near-surface region of the semiconductor alloy and thus, during segregation annealing, partial re-crystallisation (depending on the temperature) occurs leading to large variations in the mass transport. From this viewpoint, semiconductors differ largely from metallic solid solutions.