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We present a theoretical approach to study the dependence of the electron mobility on the dopant species in n-doped silicon under low electric fields. The electron charge distribution of the impurities is calculated by the Thomas-Fermi theory using the energy functional formulation. Ionized impurity scattering has been treated within the Born approximation. Our model accounts for degenerate statistics, dispersive screening and pair scattering, which become important in heavily doped semiconductors. The dielectric function is accurately approximated by a rational function. A new expression for the second Born amplitude of a Yukawa-like charge distribution is derived, which now depends on the atomic and electron numbers of the impurity ion. Monte Carlo simulations including all important scattering mechanism have been performed in the doping concentration range from 10 15 to 10 21 cm Ϫ3. The agreement with experimental data is excellent. The results confirm the lower electron mobility in As-doped silicon in comparison to P-doped silicon.

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Band gap narrowing is one of the crucial heavy-doping effects to be considered for bipolar devices. We present a new band gap narrowing model which considers the semiconductor material and the dopant species for arbitrary finite temperatures. As the minority carrier mobility is of considerable importance for modeling advanced n-p-n bipolar transistors, we implemented the new universal low field mobility model [1] in MINIMOS-NT [2]. This model distinguishes between majority and minority electron mobilities on one hand, and between different dopant species on the otheF hand, both as a function of temperature and dopant concentration. This unified treatment is especially useful for accurate device simulation. As a particular example we present the results for SiGe HBT.