Scaling analysis of the low temperature conductivity in neutron-transmutation-doped Ge-70 : Ga

We report on the scaling analysis of low temperature electron transport pro perties of nominally uncompensated neutron-transmutation-doped Ge-70:Ga sam ples in the critical regime for the metal-insulator transition. Ga concentr ation (N) and temperature (T) dependent conductivities sigma(N,T) are shown to collapse onto a single universal curve using finite temperature scaling of a form sigma(N,T) proportional to T-x f(\N/N-c - 1\/T-y) with x approxi mate to 0.38 and y approximate to 0.32 for the very small region of N = N-c +/- 0.004N(c). The conductivity critical exponent mu = x/y = 1.2 +/- 0.2 f ound from this analysis is significantly larger than mu approximate to 0.5 found from the analysis we performed previously on the same series of sampl es covering the much larger region of the concentration N-c < N < 1.4N(c). Determination of the true critical region, either N = N-c +/- 0.4% or N = N -c +/- 40%, is necessary in the future for the reliable determination of mu in Ge:Ga.