A model of ohmic contacts to semiconductors

A unified and detailed model of both thermionic and tunneling ohmic contacts to semiconductors is described. The model takes into account the actual profile of the energy barrier as it is determined by the difference between the metal work function and the semiconductor electron affinity, by the ionized impurities in the semiconductor, by the interfacial quantum electric dipole and by the classical and quantum penetration of the charge carriers into the depletion layer. The current, above and below the energy barrier peak, is computed by using the Kemble generalized transmission coefficient, by taking into account the anisotropy of the effective masses as well as their dependence on impurity-concentration, and by employing the Fermi-Dirac statistics. Good agreement between theoretical and experimental results is observed. The model enables the design of ohmic contacts to semiconductors, i.e. the determination of the semiconductor impurity concentration required to achieve pre-assigned features.