Dislocation contrast on X-ray topographs under weak diffraction conditions

Abstract

The contrast of dislocations in 4H-SiC crystals shows distinctive features on grazing-incidence X-ray topographs for diffraction at different positions on the operative rocking curve. Ray-tracing simulations have previously been successfully applied to describe the dislocation contrast at the peak of a rocking curve.The present work shows that the dislocation images observed under weak diffraction conditions can also be simulated using the ray-tracing method. These simulations indicate that the contrast of the dislocations is dominated by orientation contrast. Analysis of the effective misorientation reveals that the dislocation contrast in weak-beam topography is more sensitive to the local lattice distortion, consequently enabling information to be obtained on the dislocation sense which cannot be obtained from the peak.

Dislocation Climb in AlN Crystals Grown at Low-Temperature Gradients Revealed by 3D X-ray Diffraction Imaging

“…The displacement fields of dislocations and their effect on XRT or other diffraction contrast images are well understood. − Although it is still rather uncommon, MB-XRT (or “rocking curve imaging”) allows the quantification of these displacement fields and a direct comparison to theory . Another consequence is the apparent shift of the dislocation when inverting the sign of the angular detuning from the Bragg condition (used to achieve weak-beam contrast) as shown in Figure .…”

“…25 Monochromatic beam X-ray topography (MB-XRT), also referred to as double-crystal or plane-wave topography, allows enhancing the resolution for the imaging of dislocations by exploiting the so-called weak-beam contrast. 26,27 The typical energy bandwidth of ΔE/E ∼ 10 −4 of a double-crystal monochromator in combination with a highly parallel beam allows the strong suppression of diffraction signals from undistorted crystal regions, while selectively highlighting sufficiently distorted crystal regions only close to the dislocation cores. This leads to dislocation images with very narrow lines� usually with a width of only a few micrometers�and thus to an enhanced spatial resolution as compared, e.g., to WB-XRT.…”

Quantitative analysis of dislocations in 4H-SiC wafers using synchrotron X-ray topography with ultra-high angular resolution

“…However, the contrast of the defect is determined not only by the overlap or separation of diffracted X-rays but also by the intensity of individual X-rays following diffraction. Therefore, in order to apply ray-tracing simulations to interpret the dislocation images in synchrotron weak-beam topography (Peng, Ailihumaer, Liu et al, 2021) or plane-wave topography, the intensity of each of the diffracted X-ray beams must be taken into consideration.…”

“…It is almost impossible to distinguish the sign of the Burgers vectors since there is no additional contrast outside the circle. Previous work by Peng, Ailihumaer, Liu et al (2021) showed that additional dislocation features could be revealed when the topographs were recorded on the flanks of the rocking curve where the maximum strain sensitivity is obtained (Klapper, 1996). In 0008 SXPWT, however, we show that even without going to the flanks the dislocations already exhibit distinct features on the topographs, since the RC width is more than one order of magnitude narrower and there is significant slope even near the peak.…”

“…The orientation contrast formation mechanism is defined as an inhomogeneous intensity distribution caused by the overlap or separation of diffracted X-rays according to the local lattice misorientation generated by the dislocations. Furthermore, the orientation contrast model can be modified by incorporating the rocking curve (RC) of the sample to describe the intensity of diffracted X-rays as a function of the deviation from the perfect Bragg angle (Peng, Ailihumaer, Liu et al, 2021). If the diffraction takes place at the peak of the RC, the lattice misorientation around the defects will reduce the diffraction intensity, and the sensitivity to the lattice misorientation is determined by the RC width.…”