Variation in the effective Richardson constant of a metal-silicon contact due to metal-film thickness

Metal-Si Schottky contacts have been made by using various metals in order to investigate the dependence of typical diode parameters, such as the barrier height and the effective Richardson constant, on a film thickness of the metal electrode. In any contact with a metal-electrode film below 400 Å thickness, the Schottky barrier height evidently varies with the film thickness. The effective Richardson constant obtained by a photoelectrical measurement shows different values, depending upon the choice of metal, and also shows a metal thickness dependence, contrary to the generally accepted theory for metal-semiconductor contacts. In particular, the effective Richardson constant in a sample made by rf sputtering shows a much larger film thickness dependence than that in a sample by vacuum evaporation.