New Approach for Determination of the Critical Behavior of Conductivity near the Metal-Insulator Transition in Doped Semiconductors

Three peculiarities of the metal-insulator transition in the vicinity of the critical impurity concentration N_c are discussed: (i) The temperature dependences of conductivity σ(T) for barely metallic samples are almost parallel. This allows to suggest a new method for determining at non-zero temperatures the value of the critical exponent μ in the scaling behavior of σ(0). It is shown that μ = 1 for different impurities in Ge and Si. (ii) The temperature-independent conductivity at N > N_c is proposed to be considered as the Mott minimal metallic conductivity σ_M. It is shown that σ_M normalizes the scaling behavior of σ(0) for various impurities, (iii) The temperature-induced delocalization at T > T_d is observed for barely insulating samples. The values of T_d are normalized by the mean energy of the Coulomb interaction.