The choice of germanium as a substrate for CdTe and HgCdTe (MCT) epitaxial films is discussed. Ge appears to be a good candidate to solve the weakness of CdTe homosubstrates. Direct growth of CdTe(331) B 4° off epitaxial films was achieved on a Ge (001) substrate tilted 8° around [11¯0] by molecular beam epitaxy (MBE). Hence MCT(331) 4° off MBE epilayers were grown and characterized. The surface morphology was smooth and mirrorlike. X-ray double-crystal rocking curve on (331) planes showed full-width at half-maximum of 130 arc sec. Transmission electron microscopy is also reported to show the misfit accommodation at the CdTe/Ge interface; two domains were observed close to the interface but only a (331) orientation remained after a 50-nm-thick growth. The first photodiodes on MCT on Ge were fabricated and exhibited high performances: for a cutoff wavelength value of 5.24 &mgr;m atT=77 K,the shunt impedance measured was6.6×109 &OHgr;and theR0Aproduct was1.8×105 &OHgr; cm2.©1997 American Institute of Physics.