Diamond (SC-HPHT-D) of hitherto unavailable large volume can now be synthesized. Samples of exceptionally good mosaic spread are obtained by controlled precipitation of carbon from solutions in molten metals and alloys (typically cobalt, iron, nickel) . According to the presence and form of the major atomic-scale impurities, which is nitrogen and boron, diamond has been classified into four main types: Ia, Ib, IIa,IIb. Stimulated and guided by Professor Friedel Sellschop, who has very unfortunately past away in last summer, we started to test HPHT diamond. We are striving on one hand for radiation-hard particle detectors suitable for time- and energy resolution, investigating on the other hand the suitability of the material for electronic devices. In 2002, the work was focused on the investigation of Ib type material produced in Johannesburg. There are indications that this type of diamond has the best crystalline structure, although it contains hundreds of ppm nitrogen but in a singlesubstitutional form (P1 centres) only. Three samples of a homogeneous transparent dark yellow color have been characterized. 1 Photoconductivity In order to compare the defect-state concentrations, photoconductivity measurements have been performed. In Figure 1 the Photo-Current (PC) obtained irradiating the samples with different lamps is plotted against the energy of the incident photons. The PC is normalized to the number of photons and to the thickness of the diamond probes. PC norm. to γ's and
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