Upper limit on room-temperature diffusion of metal impurities interstitially dissolved in amorphous Si

Impurity profiles of Cu and Ag in amorphous silicon were studied before and after one year storage at room temperature and found to be indistinguishable. Since just before storage, hydrogen had been ion implanted into the uniformly metal doped layer, a diffusivity in excess of 3 x [10.sup.-24] [m.sup.2]/s would have led to an observable change in the impurity profile. Therefore the room-temperature diffusivity must be less than that (3 x [10.sup.-24] [m.sup.2]/s), which in turn implies one of two possibilities: either the interstitial diffusivity is much lower than previously determined, or the metal impurities were not fully detrapped by the implanted hydrogen. A subsequent thermal anneal at 450°C confirmed that the detrapping and diffusion of Ag and Cu in H-implanted amorphous Si conforms to its normal behaviour. The low value of the room-temperature diffusivity is important for the interpretation of forthcoming measurements on high-energy ion tracks in amorphous Si. PACS Nos.: 66.30.J-, 71.55.Jv, 61.72.uf, 81.05.Gc Nous avons etudie les profils d'impurete de Cu et de Ag dans du silicium amorphe, avant et apres remisage d'un an a la temperature de la piece et nous observons qu'ils sont indiscernables. L'implantation ionique d'hydrogene dans la couche dopee metalliquement aurait cause un changement observable dans les profils d'impurete si le coefficient de diffusion avait ete plus grand que 3 x [10.sup.-24] [m.sup.2]/s. Ce coefficient est donc plus petit que 3 x [10.sup.-24] [m.sup.2]/s, ce qui implique deux possibilites. Soit que la diffusivite est plus faible que determinee precedemment, soit que les impuretes metalliques n'ont pas ete liberees de leur piege par l'hydrogene. Un recuit subsequent a 450°C confirme que la liberation et la diffusion de Ag et Cu dans du Si amorphe avec implantation de H sont conformes au comportement normal. La basse valeur du coefficient de diffusion a la temperature de la piece est importante dans l'interpretation de mesures a venir de trajectoires d'ions de haute energie dans du Si amorphe. [Traduit par la Redaction]
Introduction Metals such as Cu, Ag, and Au are known to be very fast diffusers in crystalline (c-) Si [1] and Ge [2]. In the study of amorphous silicon (a-Si), [...]