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 ii the vicinity of the critical impurity concentration N-c are discussed: (i) The temperature dependences of conductivity sigma(T) for barely metallic samples are almost parallel. This allows to suggest a new method for determining at, non-zero tem peratures the value of the critical exponent mu in the scaling behavior of sigma(O). It is shown that mu = 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 sigma(M). It is shown that sigma(M) nor malizes the scaling behavior of sigma(O) 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.