Influence of the disorder in doped germanium changed by compensation on the critical indices of the metal-insulator transition

We present a critical review of the present status of the critical exponent puzzle of the metal-insulator transition of doped semiconductors with the emphasis on the role of mcsos- and macroscopically inhomogeneity caused by the disorder of intended or unintended acceptors and donors in the crystals. By using both the isotopic engineering and the neutron transmutation doping (NTD) of Germanium we found for low compensations (at K = 1.4 and 12%) that the critical exponents of the localization length and the dielectric constant are nearly v = 1/2 and ζ = 1, which double for medium compensations (at K = 38 and 54%) to v = 1 and Ç= 2, respectively.