Investigation of the cross-hatch pattern and localized defects in epitaxial HgCdTe

The cross-hatch pattern in epitaxial HgCdTe layers grown by Hg-melt LPE on (111)CdZnTe substrates has been investigated by several means including x-ray topography. Whenever present, the pattern is detectable by x-ray, being aligned along the <110> directions in the surface plane with a spacing of about 100 to 200 μm. A surface-relief manifestation of the cross hatch, however, exhibits the same orientation but with a smaller spacing. A surface pattern having only 10 nm of relief was found by optical profilometry mapping. Misfit dislocations are displaced from the layer/substrate interface and appear to follow the same symmetry but do not have the same spacing as the other features. The mechanisms interrelating the cross-hatch phenomena and connecting them to cross hatches in detector array performance are difficult to identify. In addition, an array of photovoltaic LWIR HgCdTe detectors in MBE-grown HgCdTe was examined in detail according to a failure analysis protocol, in order to characterize the material defects and correlate them with pixels that have higher than normal leakage current. Large, medium, and small morphological defects were seen before and after decorative etching. The large kind are most likely the funnel-shaped "void" defects, and are accompanied by several dislocations. About 63% of the failed diodes contained observable material defects.