On the Determination of the Metal-Insulator Work Function by Photoelectric Measurements

Values reported for Al/Al2O3 from tunnel current-voltage characteristics for Al/Al2O3/Al range from 1.6 to 2.5 eV, and from a method based on the Richardson-Schottky equation for thermionic emission, from 0.7 to 1.15 eV. Photocon ductivity results generally agree well with tunnel measure ments. Using microscope slides with evaporated base Al, Al2O3 films were formed by thermal oxidation or anodizing in H3BO3 + NaOH (pH 6) or 0.5N ammonium salicylate in dimethylformamide. Electrodes of 99.999per cent Al foil were also anodized in 0.01N salicylate. The photoresponse curve was the same for thermal and anodic films, film thicknesses 5.5-200.0 nm and for Al or Zn cathodes or an electrolyte as bulk emitter. The process is bulk-limited, and the photoactivation energy must be determined by the method of Moss, giving 2.75 + 0.05 eV. The existence of an internal photoeffect in the Al2O3 films throws doubt on the method of applicability. The Richardson-Schottky equation method is considered the most appropriate. 19 ref.--EPAA/AF.