Temperature Dependent Model for Hole Effective Mass in Heavily Doped p-type SiGe

Abstract
As a consequence of compressive strain and alloying, the hole effective mass in p-type strained SiGe differs significantly from its Si value. Influencing the carrier concentrations in the base, the hole effective mass affects the base transport properties of npn SiGe HBTs. A new model for hole effective mass is presented in this work, which takes into consideration the dependence on temperature, doping concentration and germanium fraction. The model is based on experimental data and theoretical studies of the valence band structure supported by the detailed numerical analysis of hole effective mass. It is suitable for efficient analysis and optimization of SiGe HBTs, and can be tuned to the measurements of carrier transport. The model is valid in the temperature range from 77K to 300K, for doping concentrations up to 10²⁰cm^-3 and for germanium fractions up to 0.2.