PHOTOCURRENT MEASUREMENTS ON THIN PASSIVE FILMS AT HIGH LOCAL RESOLUTION

Photocurrent spectra i(ph)(lambda) and UV laser scanning measurements at high lateral resolution for the investigation of local properties o f the Ti/TiO2 system are presented. The measurements are carried out o n Ti single crystals of known orientation. It is emphasized and proved that the interpretation of i(ph) values requires consideration of mul tiple internal reflections within the ultrathin TiO2 layers. An extend ed Butler-Gartner model is applied which explains the i(ph)(d)-curves. The model enables determination of both electronic and optical layer properties such as optical constants, extension of the space charge la yer, and defect state concentration. These layer quantities are correl ated with the crystal orientation of the Ti substrate. Thickness depen dent photocurrent measurements on oxide thickness gradients generated by UV laser illumination showed an excellent qualitative agreement wit h simulations according to the model in a wide thickness range. The la rgest growth factor for the laser induced oxides was found for the (00 01) orientation, which is the densest packed surface. The oxide gradie nt generated on this surface covered the range from 30 to 80 nm. In th is range, i(ph) runs through one maximum and a successive minimum as p redicted by the theory. However, the comparison of electronic paramete rs ((epsilon(O)/N-D)-values) determined by a fit according to this mod el and impedance measurements still shows significant deviations deman ding further improvement of the model.