THE EXAMINATION OF THE INFLUENCE OF A SPACE-CHARGE LAYER ON THE FORMATION KINETICS OF THIN PASSIVE FILMS BY SCHOTTKY-MOTT ANALYSIS

Passive layers are treated as highly doped semiconductors with an amorphous character. The donor number obtained experimentally is about N almost-equal-to 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(ox) = 1-100 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 films. Near the phase boundary to the metal a region without an electric field will be established. The rate determining step for TiOx is the field assisted transport. For FeOx, the rate determining step changes from a field assisted transport at thin layers to a thickness controlled mechanism at thicker layers.