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

Abstract

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 × 10−24 m2/s would have led to an observable change in the impurity profile. Therefore the room-temperature diffusivity must be less than that (3 × 10−24 m2/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.