Determination of metallic impurities in high-purity type IIa diamond grownby high-pressure and high-temperature synthesis using neutron activation analysis

Metallic impurities in high-purity type IIa and conventional type To diamon d single crystals grown by high-pressure and high-temperature (HPHT) synthe sis were determined by neutron activation analysis using thermal neutrons. Metallic impurities of Fe, Co, Cr and other minor elements were detected in the high-purity type IIa diamond crystal. The typical quantities of these metallic impurities were a few ppb. The influence of these metallic impurit ies on the electrical properties of the type IIa diamond crystal was practi cally negligible compared with nitrogen and boron impurities behaving as a donor and an acceptor, respectively. In addition to the impurities detected in the type IIa diamond crystal, Ni impurities of several hundreds of ppb were detected in conventional type Ib diamond crystals. A difference in mol ten metal solvents used in the synthesis of each diamond crystal resulted i n the difference in metallic impurities. (C) 2000 Elsevier Science B.V. All rights reserved.