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Homoepitaxial chemical vapour deposition (CVD) on high pressure, high temperature (HPHT) synthetic diamond substrates allows the production of diamond material with controlled point defect content. In order to minimize the extended defect content, however, it is necessary to minimize the number of substrate extended defects that reach the initial growth surface and the nucleation of dislocations at the interface between the CVD layer and its substrate. X-ray topography has indicated that when type IIa HPHT synthetic substrates are used, the density of dislocations nucleating at the interface can be less than 400  cm(-2). X-ray topography, photoluminescence imaging and birefringence microscopy of HPHT grown synthetic type IIa diamond clearly show that the extended defect content is growth sector dependent. ⟨111⟩ sectors contain the highest concentration of both stacking faults and dislocations but ⟨100⟩ sectors are relatively free of both. It has been shown that HPHT treatment of such material can significantly reduce the area of stacking faults and cause dislocations to move. This knowledge, coupled with an understanding of how growth sectors develop during HPHT synthesis, has been used to guide selection and processing of substrates suitable for CVD synthesis of material with high crystalline perfection and controlled point defect content.

Single crystal CVD synthetic diamond samples grown on (001) substrates have been studied using X‐ray topography, photoluminescence imaging, cathodoluminescence imaging and transmission electron microscopy. X‐ray section topographs sampling a plane very close to the surface of a (010) cross‐sectional slice show contrast that is closely correlated with photoluminescence image contrast relating to differences in incorporation of point defects on step risers and terraces during growth. The point defect content is too low to influence X‐ray topography contrast and therefore the correlation suggests a difference between the dislocation content for terrace and riser growth. Dislocations imaged in cathodoluminescence have been observed to follow paths that are strongly influenced by step flow during growth. Transmission electron micrographs show [001] dislocations with sections of <110> 60° or edge dislocations in configurations consistent with formation as a result of step flow growth. It is proposed that a passing riser can cause dislocations to switch from [001] to [101] line direction when this minimises the increase in the energy associated with the dislocation as riser growth proceeds. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

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