Determination of observable depth of dislocations in 4H-SiC by X-ray topography in back reflection

We performed X-ray topography using the asymmetric 1128 back-reflection by changing the incident X-ray energy (E) in order to evaluate the observable depth (t(obs)) of dislocations in 4H-SiC(0001) wafers with a 4 degrees off-axis angle toward the [1120]-direction. Since the incident angle (omega) of the X-rays satisfying the Bragg condition changed along with E, the observable length of the straight segment of the basal plane dislocation (BPD) on the X-ray topographs also changed. The t(obs) values were determined from the observable length of the straight BPD segment, and consequently, plots of t(obs) versus E, and tobs versus omega were obtained. We discussed the relationships between tobs and the absorption depth (t(mu)), between t(obs) and the extinction depth (t(Lambda)), and between tobs and t(Lambda)/t(mu) as criteria of the dislocation visibility, and we found that the plot of t(obs) versus t(mu) was described as t(obs) similar to 0.75t(mu) with good linearity. (C) 2017 The Japan Society of Applied Physics