Mapping of CdZnTe substrates and CdHgTe epitaxial layers by X-ray diffraction

A simple procedure is described for mapping of lattice parameter and X-ray rocking curve width across Cd1-yZnyTe (CZT) substrates and CdxHg1-xTe (CMT) epitaxial layers. It is shown how screening of the crystallinity and composition of CZT substrates can be utilized to make subsequent X-ray characterizations of epitaxial layers more reliable. This also allows selection of substrates with a close lattice matching to a given CMT composition, to reduce or avoid layer relaxation. Substrates with laterally Varying Zn content give a Varying lattice mismatch on a single epitaxial layer. Correlation of the lattice parameter maps of substrate and layer shows the resulting variations in layer strain, and the onset of relaxation can be clearly identified. Mapping of rocking curve peak widths on good quality CZT substrates and closely lattice matched CMT layers shows that the peak width can be below 6 arcsec, limited essentially by the intrinsic peak width of the materials. Additional broadening of the layer peaks is introduced primarily by substrate defects and misfit dislocations, unless epitaxial growth conditions deviate significantly from their optimum.