Method of four coefficients in the presence of multiple carrier scattering mechanisms

In the “method of four coefficients,” experimental electrical resistivity, Seebeck coefficient, Hall coefficient and Nernst coefficient of a material are fitted within Boltzmann transport theory at temperature T to extract four material parameters, e.g. the charge carrier mobility, carrier concentration, density of states effective mass, and scattering exponent λ. In the present work, we evaluated the practice of modeling the relaxation time energy dependence using a single effective scattering exponent λ_eff when multiple scattering mechanisms are present. Since the use of a single λ_eff is not directly justified by Mattheisen’s rule for scattering rates when multiple scattering mechanisms are present, the interpretation of the obtained λ_eff is not entirely well-defined. We therefore performed an evaluation to determine what information on individual scattering mechanisms and their relative contributions to the overall relaxation time might be extracted from λ_eff. Alternative approaches to fitting the experimental data by including the temperature dependence of the transport coefficients will also be discussed.