CHARACTERIZATION OF TITANIUM PASSIVATION FILMS BY IN-SITU AC-IMPEDANCE MEASUREMENTS AND XPS ANALYSIS

Capacitance-potential measurements by ac impedance methods have shown that for polarisations of 0.5 to 0.7 V from the flat band potential, t itanium passivation films formed between 0.2 and 2 V (thicknesses rang ing from 15 to 100 Angstrom) display Mott-Schottky behaviour, with fre quency dependent slopes. This study develops a theoretical approach wh ich takes account of the frequency dispersion and allows the determina tion of flat band potentials, donor densities, and Helmholtz capacitan ces for the films. The Mott-Schottky behaviour was attributed to the p resence of Ti3+ as the doping element. Experimental evidence for this was obtained from XPS spectra. For films formed above 2 V the linear M ott-Schottky region was difficult to define, and capacitance vs. poten tial plots resembled the behaviour of amorphous semiconductors.