CdTe/Si substrates with etch-pit densities ~5 x 104 - 2 x105 cm-2 and x-ray diffraction full-width at half-maximum <60 arcsec over >60% of a 3" substrate and ≤85 arcsec over the entire area are now available. Midwave and shortwave HgCdTe infrared detectors fabricated on these substrates have device characteristics as good as those of detectors fabricated on lattice-matched CdZnTe substrates. Also, minority carrier lifetimes of 100s of nanoseconds are measured for CdTe/Si and CdZnTe/Si, and both can be p-doped 1017 cm-3 and n-doped >1020 cm-3. Calculations suggest that the use of these materials should yield multijunction solar cells with efficiencies higher than those of the corresponding III-V multijunction cells at much lower cost, using rugged, large-area, inexpensive active Si substrates. The first CdZnTe/Si single-junction solar cells fabricated by EPIR displayed an electronic-charge times open-circuit voltage, qVoc, within ~0.45 eV of the CdZnTe bandgap Eg, as good a result as that for the best III-V alloy single-junction cells, and confirmed the suitability of single-crystal CdZnTe/Si for the manufacture of high-efficiency solar cells.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.