Synchrotron Bragg diffraction imaging characterization of synthetic diamond crystals for optical and electronic power device applications

Abstract

Bragg diffraction imaging enables the quality of synthetic single-crystal diamond substrates and their overgrown, mostly doped, diamond layers to be characterized. This is very important for improving diamond-based devices produced for X-ray optics and power electronics applications. The usual first step for this characterization is white-beam X-ray diffraction topography, which is a simple and fast method to identify the extended defects (dislocations, growth sectors, boundaries, stacking faults, overall curvature etc.) within the crystal. This allows easy and quick comparison of the crystal quality of diamond plates available from various commercial suppliers. When needed, rocking curve imaging (RCI) is also employed, which is the quantitative counterpart of monochromatic Bragg diffraction imaging. RCI enables the local determination of both the effective misorientation, which results from lattice parameter variation and the local lattice tilt, and the local Bragg position. Maps derived from these parameters are used to measure the magnitude of the distortions associated with polishing damage and the depth of this damage within the volume of the crystal. For overgrown layers, these maps also reveal the distortion induced by the incorporation of impurities such as boron, or the lattice parameter variations associated with the presence of growthincorporated nitrogen. These techniques are described, and their capabilities for studying the quality of diamond substrates and overgrown layers, and the surface damage caused by mechanical polishing, are illustrated by examples.

Relationship between Birefringence and Surface Morphology in Single‐Crystal Diamonds Grown by MPCVD

“…This phenomenon is related to the growth of sample 2. X‐ray white topography is a method used to examine the microstructure defects of crystal material, and it is widely used in the study of the integrity of crystal material . Figure a shows an X‐ray white morphology image of HPHT type Ib seed substrate, showing the defects of the seed substrate and their distribution.…”

Substrate Effects on Charge Carrier Transport Properties of Single‐Crystal CVD Diamonds and an 8 mm Square Radiation Energy Spectrometer

“…However, this difficulty did not occur on HP/HT type IIa substrates with a few ppm of nitrogen impurities. The impurity amount of “general grade” single‐crystal CVD diamond (Element Six Ltd.) is unknown, but it is presumably equal to or smaller than that of HP/HT type IIa: it is described elsewhere in the literature as less than 5 ppm in “optical grade” elsewhere in the literature …”

“…Regarding crystallinity, an earlier study reported synchrotron radiation topography for single‐crystal CVD (low‐grade) (Element Six Ltd.), HP/HT type Ib single‐crystal (Sumitomo Electric Industries, Ltd.), and HP/HT type IIa single‐crystal diamond (Element Six Ltd.). Although produced by different manufacturers, HP/HT type IIa crystal shows the least dislocation.…”

Comparison of the quality of single-crystal diamonds grown on two types of seed substrates by MPCVD

“…The rocking curves of the two types of seed substrates and CVD layers grown on each were measured by a Bruker D8 DISCOVER X-ray high-resolution diffractometer using a monochromized Cu-Kα1 X-ray source with a Ge (220) four-crystal monochromator. X-ray topography is a powerful tool for studying extended defects such as dislocations and stacking faults [23,24]. X-ray topography was performed on two types of seed substrates and the samples grown on each.…”

“…(c, d) X-ray topography images of as-grown CVD seed substrate. The X-ray rocking curve is very sensitive to dislocations and other defects in the crystal, and the quality of the crystal can be judged according to the FWHM of rocking curve [23]. When the dislocation density is high (10 4 -10 7 cm -2 ), the dislocation density (Nd) of the sample can be calculated from the FWHM of rocking curve, which was calculated by the formula [33]: Nd=(△θ1/2) 2 /9b 2 , where △θ1/2 and b are the real FWHM of the double crystal diffraction of a specimen crystal and Burgers vector length, respectively.…”