Quantitative analysis of delocalization in the vicinity of the metal–insulator transition in doped semiconductors

Abstract. A temperature-induced crossover from hopping to metallic conductivity is observed for barely insulating samples of Ge:As and Ge:Sb with impurity concentration N just below the critical value Nc0. The values of the correlation length are obtained on both sides of the transition. A method is developed for determination of a ‘delocalization temperature ’ Td, which separates the hopping and metallic conductivity. It is shown that the dependence of Td on N for various semiconductors can be reduced to a universal curve using normalization of the T-scale by the mean energy of the Coulomb interaction W D.e2=0/N1=3c0. The metal–insulator transition (MIT) is defined by the vanishing of the dc conductivity at zero temperature [1]: the value of .0 / .T! 0 / when plotted as a function of the impurity concentration N, is equal to zero on the insulating side of the MIT and remains finite on the metallic side, obeying scaling behaviour in the vicinity of the transition [2]: .0 / D γ e 2 h