## 2 Materials and Methods  
Single crystals of silicon carbide are grown industrially for high-power electronic applications. The experiment was carried out at the beamline ID06-HXM of the ESRF [14] on a commercially produced 0.35 mm thick single crystal wafer of 4H-SiC. The surface orientation of our sample was nearly (0001), with a 4\({}^{\circ}\) offset towards the [10\(\overline{1}\)0] direction. We studied the \(\left(40\overline{4}0\right)\) reflection in transmission mode (Laue geometry) using an X-ray beam energy of 10 keV with \(\Theta_{\text{B}}\) = 14.6\({}^{\circ}\). The beam size was 1 \(\times\) 1 mm\({}^{2}\). An indirect two-dimensional detector with an effective pixel size of 0.6 \(\times\) 0.6 \(\upmu\)m\({}^{2}\) (leading to a field of view of 1.2 \(\times\) 1.2 mm\({}^{2}\)) was positioned approximately 40 mm downstream of the sample. The experimental technique we used is Rocking Curve Imaging (RCI), which gives access to quantitative data associated with crystal distortion with a spatial resolution in the \(\upmu\)m range. RCI is an extension of monochromatic Bragg diffraction topography. Experimentally, it is performed by recording a series of images (200 in the present work) at slightly different consecutive angular positions on the Bragg diffraction curve (\"rocking curve\") using a two-dimensional pixelated detector (Figure 1). The data recorded along the rocking curve are processed and analysed pixel by pixel using purpose-built software [15]. Maps of the \"local\" integrated intensity, Full Width at Half-Maximum (FWHM) and peak position are then generated from the rocking curves recorded in each pixel. The last two maps result from a Gaussian fit of the rocking curve recorded on each individual pixel, as schematically indicated in Figure 1.  
RCI was developed using synchrotron radiation because it is difficult to implement with conventional laboratory X-ray equipment. In particular, the number of photons recorded in a given pixel of the detector (with a surface typically in the 1 \(\upmu\)m\({}^{2}\) range) should be statistically meaningful, which implies that a high photon flux and a bijective (reversible) relationship between one pixel of the detector and one voxel in the crystal should exist. Figure 1: RCI technique: (**a**) the sample is in Bragg position for a chosen reflection; the diffracted intensity is recorded by a pixelated detector. (**b**) A series of images (\(\sim\)200) is recorded for different angular positions (rotation \(\omega\)) along the rocking curve corresponding to the whole sample; a few representative images along the rocking curve of the 4H-SiC crystal are displayed. (**c**) RCI maps generated from the rocking curves recorded on each of the pixels of the detector show the variation across the crystal of the integrated intensity, peak width and peak position (in \(\omega\)). This implies a low divergence beam. This technique was initially implemented in the reflection geometry [10] and was used for the characterisation of crystals and deposited layers with thicknesses in the \(\upmu\)m range [12]. In order not to be limited to the near-surface distortion, we use RCI in transmission geometry. Most of our RCI work relies on two assumptions that simplify the interpretation of the various maps. We first assume that interferences, such as Kato fringes, associated with dynamical diffraction effects [16], are averaged out and that the diffracted beam recorded in a given pixel of the detector originates from a well-defined volume (\"voxel\") in the crystal that corresponds to the intersection of the incident beam with the projection of the considered pixel along the Bragg diffracted direction. We assume, in addition, that all of the beam diffracted by the considered voxel goes to one pixel of the detector; this assumption is valid when the \"mosaic spread\" in this voxel, measured by the FWHM obtained from the Gaussian fit, is small enough (smaller than \(\sim\)2 \(\times\) 10\({}^{2}\)\(\upmu\)radian for our experimental conditions).