We report a novel approach for obtaining precise control of both p-and n-type dopant concentrations in bulk Ge single crystals. High-purity Ge single crystals of controlled 74Ge/70Ge isotope composition ratios were grown and subsequently doped by the neutron transmutation doping (NTD) technique. The resulting net-impurity concentrations and the compensation ratios were precisely determined by the thermal neutron fluence and the [74Ge]/[70Ge] ratios of the starting Ge materials, respectively.

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... lication of NTD to seven crystals with 0<[74Ge]/[70Ge]<4.34 lead to p-type Ge:Ga,As with compensation ratios in the range o-0.76. The ability to grow crystals with accurately controlled Ge isotope mixtures allows us to obtain ratios anywhere between 0 and 1 for both p-and n-type doping.