Characterization of ZnTe homo-epitaxial layers by means of synchrotron X-ray topography

Synchrotron X-ray reflection topography was used to evaluate the crystal quality of a ZnTe epilayer grown by MOVPE on a low dislocation density (111) ZnTe substrate. The epilayer thicknesses were 0.35 µm and 3.0 µm, and the growth temperature was 325°C or 350°C. Another specimen whose epilayer was grown at 400°C with 3.0 µm thickness had a 0.35 µm thick buffer layer grown at 325°C. Reflection topographs and rocking curves were recorded from four equivalent 224 reflections using an X-ray wavelength of 0.1578 nm. Topographs of specimens with the epilayer grown at 325°C and 350°C did not show images of line defects, such as misfit dislocations. However, we could observe line images in the specimen with the epilayer grown at 400°C and with the buffer layer grown at 325°C. The line images were not observed in transmitted X-ray Laue topographs using a white X-ray beam. Therefore, it was concluded that the line defects existed in the epilayer and not the substrate. In addition, topographs taken with other diffraction planes showed the same images except for reversed image contrast. Therefore, the defects did not have characteristic strain fields such as for dislocations, and they are stacking faults grown in the epilayer during high temperature growth.