Metal-Insulator Transition in Homogeneously Doped Germanium
  We have measured the electrical conductivity of Ge:Ga samples prepared by neutron-transmutation doping of isotopically enriched 70Ge single crystals in order to study the metal-insulator transition (MIT) ruling out an ambiguity due to inhomogeneous distribution of impurities. The critical exponent for the zero-temperature conductivity is 0.5 in zero magnetic field and 1.1 in magnetic fields. Variable-range-hopping conduction of the insulating samples and finite-temperature scaling analysis of the MIT induced by the external magnetic field are also discussed. 
Michio Watanabe