The examination of the influence of a space-charge layer on the formation kinetics of thin passive films by Schottky-Mott analysis

Abstract

Passive layers are treated as highly doped semiconductors with an amorphous character. The donor number obtained experimentally is about N≈10 20 cm -3 and decreases with increasing film thickness. The extension of the resulting space-charge layer d sc will reach some nm only and approaches the thickness of the passive layers ( d ox1−100 nm). This contradicts common models of the kinetics of layer formation, which assume a linear potential drop within the film. The influence of the space-charge layer is examined for the oxide layer formation on Ti and Fe. The carrier distribution is determined by C(U)-measurements using a special pulse technique. It is now possible to realize one C(U)-cycle within 1 ms. d ox exceeds d sc in both systems at thicker Near the phase boundary to the metal a region without an electric field will be established. The rate determining step for TiO x is the field assisted transport. For FeO x , the rate determining step changes from a field assisted transport at thin layers to a thickness controlled mechanism at thicker layers.