Deep-level transient spectroscopy was used to determine Pt concentrations at various depths. Inverse U-shaped Pt profiles were found after diffusion at 700C. A higher Pt concentration was found in the bulk than at the surface. Such profiles could be explained by invoking the Frank-Turnbull mechanism, if it were assumed that the initial vacancy concentration was higher than the equilibrium concentration. It was suggested that the observation of inverse U-shaped profiles implied that the diffusion process in the bulk was governed by the initial vacancy concentration, and not by vacancy equilibrium, at temperatures below about 850C.

H.Zimmermann, H.Ryssel: Applied Physics Letters, 1991, 59[10], 1209-11