Electrical Properties of Nonstoichiometric Semiconductors

Abstract

The electrical conductivity σ, thermoelectric power Q, and Hall coefficient R are examined as a function of the ratio of hole‐to‐electron concentrations p/n for a nondegenerate semiconductor at constant temperature. From these relations the fundamental parameters of the material (forbidden band gap, mobilities, and effective masses) can be derived. This approach is particularly applicable to materials whose stoichiometry varies as a function of temperature and vapor pressure of the constituents P. For any model of this equilibrium decomposition, it is easy to transform the calculations in terms of p/n into results as a function of P. As p/n increases, σ passes through a minimum, while Q and R traverse minimum (negative), zero, and maximum (positive) values. These extrema are of special interest. In the simple case of one kind of imperfection, σ, Q, and R become independent of P in a certain pressure range (i.e., when the intrinsic condition n=p has been reached). It is then possible to derive the ratio of mobilities μ_n/μ_p and the ratio of the average effective masses m_n*/m_p* from σ(P) and Q(P) only. Hence, if μ_n or m_n* are known (i.e., from measurements at lower temperatures), one can calculate these parameters for the other charge carrier.