Residual strain around grown-in defects in CVD diamond single crystals: A 2D and 3D Raman imaging study

Abstract

Single crystal diamond grown by chemical vapor deposition (CVD) sometimes exhibits strain induced birefringence arising from bundles of dislocations lying almost parallel to the [001] growth axis. Some of these specific birefringence patterns consist of four or eight bright petals, depending of the observation conditions. The present study reports results of a Raman imaging investigation of such defects. A specific homoepitaxial film still attached to its substrate, which contained a few of these defects, has been studied. Point by point mapping was used to visualize structural features at certain depths inside the crystals to produce either 2D or 3D tomographic images. These defects were easily detected in the Raman images, with specific line intensity, frequency, and width contrasts. Systematically, dislocations were found to nucleate at the epitaxial interface. In each case, dislocation nucleation was caused by particulate (carbon) contamination. High compressive strain was evidenced in the vicinity of the carbon particles, which was found to decrease in magnitude as the film grew in thickness. Dislocation walls were revealed by the width images. In most cases, 4-arm patterns lying along < 110 > directions were evidenced, but sometimes, more complex features were observed. Finally, polarized Raman measurements gave intensity contrasts that were rather similar to those seen in the birefringence images. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim