Rectification Properties of Metal Semiconductor Contacts

Metal semiconductor contacts of a number of different metals were made on n- and p-type germanium using jet etching and plating techniques. Current voltage curves taken on 12 of these metals on 5 ohm-cm n-type germanium showed rectification which follows the diode equation J=J0(eqV/kT−1). No correlation was found between the reverse saturation current densities of these diodes and such properties of the metals as work function, electromotive force, etc. For those metal contacts possessing the lowest saturation current densities, calculations indicated the current crossing the contact was to a large percent hole current and that the magnitude of the hole current was controlled primarily by the geometry of the diode. All metals plated on 5 ohm-cm p-type germanium produced ohmic contacts of resistivity comparable to the spreading resistance expected for the diode geometry used. For indium diodes, a study of rectification versus resistivity indicated that the barrier produced on both n- and p-type germanium with plated contacts is one to electron flow rather than hole flow. When the assumption of only hole current crossing the barrier was made, it was shown that the I–V curves calculated from the diode theory, for different resistivities of germanium, were in qualitative agreement with the measured curves. Curves of zero voltage conductance versus temperature for different resistivities of germanium were also found to be in good agreement with those calculated on the assumption of all hole current.