Investigation of penetration depth and defect image contrast formation in grazing incidence X-ray topography of 4H-SiC wafers

Techniques utilizing the grazing incidence geometry are particularly useful for discerning defects at different depths below the crystal surface particularly for 4H-SiC epitaxial wafers. The penetration depths calculated theoretically by just considering a dislocation as simple line defect are much smaller than those measured experimentally. In our study we have developed and compared two models involving different diffracting volumes to account for this discrepancy. In one model, the image contrast is formed by simulating the density map of the diffracted beam according to the local lattice plane tilt assuming the dislocation image formation is dominated by orientation contrast. In the second model, diffracting volume for kinematical diffraction is defined by the surface over which the effective misorientation associated with the dislocation is equal to the rocking curve width of dislocations with different Burgers vectors. By comparing between measured penetration-depths in grazing incidence geometry with these two approaches, our study show that both model play a role in dislocation contrast formation mechanism.