THE EFFECTS OF IMPURITY BANDS ON THE ELECTRICAL CHARACTERISTICS OF METAL-SEMICONDUCTOR OHMIC CONTACTS

Abstract

The effects of semiconductor heavy doping on the I-V characteristics and the specific contact resistivity rho(c) of semiconductor-metal ohmic contacts have been theoretically studied by incorporating the band-edge-tailing and impurity band effects. The Fermi level and the effective conduction band edge have been recalculated to determine the electron population and the bandgap narrowing. When the available electrons with higher transmission probability, which dominate the tunneling process, have been reduced by the presence of an impurity band, the tunneling current density becomes lower and hence the specific contact resistivity becomes higher for the case with the impurity band than that without the impurity band. Considering the physical properties inherent in a heavily-doped semiconductor, it is possible to explain the deviations of the experimental data from the theoretical results obtained from the conventionally used tunneling theory for the ohmic contacts. Furthermore, by comparing the simulated results and the measured rho(c) data deduced from the Al and Ti contacts on both doping types of the Si-substrate, satisfactory agreements have been obtained.