ABSTRACTThe structural properties of LPE-grown HgCdTe on heteroepitaxial MOCVD-grown CdZnTe/GaAs/Si substrates were evaluated using high-resolution x-ray diffraction techniques and TEM. Large tilts {up to 4°} between CdZnTe layers and GaAs/Si substrates are a general characteristic of this heteroepitaxial system and are are attributed to the interaction of closely spaced misfit dislocations that arrange to form a tilt boundary. Either {112}CdTe or {552}CdTe can be grown on {112}GaAs/Si; the {552} was shown to result from a first-order twinning operation of {112}. Lamnella {111} microtwins in {111}CdZnTe/{100}GaAs/Si substrates, measured by x-ray techniques, are not readily propagated into the LPE-grown HgCdTe layer. The x-ray FWHM of the LPE HgCdTe is typically at least a factor of two lower than that of the Si-based substrate from annealing and due to the increased thickness of the layer; both mechanisms promote dislocation interaction and annihilation. High performance MWIR and LWIR HgCdTe 128×128 hybrid focal plane arrays were fabricated on these Si-based substrates. An array average of ROAj = 17.8 ohmcm2 for a cutoff wavelength of 10.8 μm at 78K was demonstrated.