Perhaps you are thinking of the Schottky barrier. (Curioisly though, in the Schottky diode they typically do use the n-doped silicon, although the p-type also f

Perhaps you are thinking of the Schottky barrier. (Curioisly though, in the Schottky diode they typically do use the n-doped silicon, although the p-type also forms the Schottky barrier with metals.)