NEUTRON TRANSMUTATION DOPING OF ISOTOPICALLY ENGINEERED GE

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 Ge-74/Ge-70 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 [Ge-74]/[Ge-70] ratios of the starting Ge materials, respectively. Application of NTD to seven crystals with O less-than-or-equal-to [Ge-74]/[Ge-70] less-than-or-equal-to 4.34 lead to p-type Ge:Ga,As with compensation ratios in the range 0-0.76. 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.