Observing defects in diamonds

Defects in crystalline materials can have a dramatic impact on the performance of devices using those materials. The ESRF’s synchrotron X-rays provide a unique method for rapid mapping of defects in crystalline materials. 

In the Green Diamond project, synchrotron X-ray topography maps were recorded for diamond substrates to show defect density distribution and the coordinates of severe defect locations of primarily bulk-to-surface defects. This was an essential prerequisite to correlate the relationship between the location of these defects and their impact on the performance of diode and transistor devices.

The ESRF’s monochromatic beam X-ray diffraction rocking-curve imaging instrument BM05 was employed using a novel methodology that is unique to the ESRF. This method enabled depth-profiling measurements of the quality of the near surface layer of substrates, the crystal-structure quality of CVD grown doped diamond epi-layers and defects at the epi-to-substrate interface.  The resulting mapping of the diamonds showed clearly that the epilayer quality depends strongly on the quality of substrate and moreover the quality of treated surface.

Figure 1. Topography map of an industrial synthetic diamond used in the Green Diamond project. A 3x3 mm2 diamond was surface treated after standard mechanical polishing and then a thin n-type doped diamond layer was grown on top. The high FWHM value (2.2 x10-3 degrees) which is presented in red signifies high crystal distortion from the surface while the blue colour (FWHM ~ 1.7x10-3 degrees) signifies good crystal quality of the bulk. Several features are noticeable in this image: (i) unidirectional striations from polishing lines, (ii) concentric arcs also due to polishing lines, (iii) surface hillock type defects surrounded by high strain fields.

For further information: Diamonds have a glittering future in green energy production

Top image: Beamline BM05