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Defects and X-ray Topography
On the left is an optical image of (the Zn surface of a) ZnO substrate
which gradually transforms into a x-ray reflection topograph. To the eye,
other than a few scratches (in this case on the rear surface), the ZnO wafer
looks clear and has a mirror finish. As the substrate is transparent, we
see both surfaces in this (scanner) image. As the Cu K-alpha x-ray wavelength
was used was in an asymmetric scattering geometry [(1 0 -1 4) reflection],
the x-rays only penetrate a few microns into the surface. For this particular
wafer, we can see that there is serious polishing damage and that the surface
needs further pretreatment before it can be used as an epitaxial template
for homoepitaxy. |