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K131The electron work function (x ) at the metal-insulator interface i s usually determined by the tunnel current-voltage characteristics of metal/insulator/metal systems. The values of x for the AI/Al 0 /A1 system, thus obtained by different 2 3 authors (1 to 3), vary in a large range from 1 . 6 to 2 . 5 eV. Another method i s based on the equation of Richardson-Schottky for thermionic emission from metals into insulators. Considerably lower values of x (between 0 . 7 and 1 . 1 5 eV) have been obtained by this method (4 to 6).Many authors (7 to 13) assume that the work function can be determined in an independent way by means of photoconductivity measurements. In some cases ( 7 , 8) the data thus obtained agree well with those determined from the tunnel characteristics, but they are in large disagreement with the values of x ionic experiments (4 to 6). obtained by therm-A possible explanation of the above discrepancies is given in the present work on the basis of some new experimental results. The spectral dependence of the photocurrent was investigated by changing both the emitting top electrode and the thickness of the dielectric layer. The specimens used were microscope slides with evaporated base aluminium. The A1203 Lilms were formed by two different methods: (i) thermal oxidation and (ii) electrolytic anodization in H BO + NH OH aqueous solution (pH = 6) o r 0 . 5 N ammonium salicylate in dimethylformamide. Electrodes of high purity aluminium foil (99.999% Al) were also anodized in 0.01 N ammonium salicylate in dimethlyformamide to obtain thick A1 0 films. Either semitransparent metal films (A1 o r Zn) or an electrolyte (the forming solution for the aluminium foil) were used as top electrode. The 3 3 4 2 3 K132 physica status solidi (a) 32

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