INVESTIGATION OF THE CROSS-HATCH PATTERN AND LOCALIZED DEFECTS IN EPITAXIAL HGCDTE

The cross-hatch pattern in epitaxial HgCdTe layers grown by Hg-melt LP E on (111) CdZnTe substrates has been investigated by several means in cluding x-ray topography. Whenever present, the pattern is detectable by x-ray, being aligned along the <110> directions in the surface plan e with a spacing of about 100 to 200 mu m. A surface-relief manifestat ion of the cross hatch, however, exhibits the same orientation but wit h a smaller spacing. A surface pattern having only 10 nm of relief was found by optical profilometry mapping. Misfit dislocations are displa ced from the layer/substrate interface and appear to follow the same s ymmetry but do not have the same spacing as the other features. The me chanisms interrelating the cross-hatch phenomena and connecting them t o cross hatches in detector array performance are difficult to identif y. In addition, an array of photovoltaic LWIR HgCdTe detectors in MBE- grown HgCdTe was examined in detail according to a failure analysis pr otocol, in order to characterize the material defects and correlate th em with pixels that have higher than normal leakage current. Large, me dium, and small morphological defects, were seen before and after deco rative etching. The large kind are most likely the funnel-shaped ''voi d'' defects, and are accompanied by several dislocations. About 63% of the failed diodes contained observable material defects.