THE RELATIONSHIP BETWEEN LATTICE MATCHING AND CROSSHATCH IN LIQUID-PHASE EPITAXY HGCDTE ON CDZNTE SUBSTRATES

X-ray topography provides a very sensitive map of lattice mismatch bet ween a HgCdTe LPE epitaxial layer and its (111) CdZnTe substrate. A we ll-defined crosshatch pattern in the three [110] directions indicates a positive room-temperature lattice mismatch. Fbr conditions of near-p erfect lattice matching (+/-0.003% mismatch), the crosshatch pattern d isappears, presumably because there are few or no misfit dislocations present near the interface, and a region free of topographic contrast is observed. The crosshatch-free region occurs for a small positive ro om-temperature mismatch (about 0.02%); this is attributed to differenc es in the lattice matching condition at room temperature and the growt h temperature. For negative mismatches, where the Film is in tension, a mosaic pattern, rather than a crystallographically oriented crosshat ch, is observed in the topograph. Rocking curve full width at half max imum of the epitaxial layer is minimized in the crosshatch-free zone w at a value nearly equal to that of the substrate. Etch pit density of the HgCdTe layer shows a strong minimum for perfect room temperature l attice matching, with values as low as 1 x 10(4) cm(-2). For nearly la ttice matched layers, crosshatch is present throughout the thickness o f the epitaxial layer except for a narrow graded-composition region ne ar the substrate interface. Crosshatch contrast appears to result from long-range strain fields associated with a misfit dislocation network near the substrate interface. Spatial variations in topographic featu res and mismatch across relatively small lateral distances are caused by variations in substrate alloy composition. For truly lattice-matche d substrates, better control over the substrate lattice parameter is r equired.