Barrier Height Studies on Metal-Semiconductor Systems

Photovoltaic and space-charge capacitance measurements have been used to study the height of the Schottky barrier at the metal-semiconductor interface of a series of metals evaporated onto ``vacuum cleaved'' samples of n-type CdS and n- and p-type GaAs. Although the barrier heights for metal-CdS samples increase with increasing metal work function as predicted by simple theory, significant deviations were noted. The barrier heights measured on metal-GaAs samples at different temperatures show very little dependence on the metal and appear to be fixed relative to the valence band edge by surface states. The results are compatible with the model in which the photoresponse, for photon energies less than the semiconductor energy gap, arises principally from photoemission of carriers from the metal into the semiconductor; however, the results are sensitive to the method of surface preparation and comparisons with other work are difficult.