SiGe single crystals with different concentrations of doping Ge in CZSi were measured by FTIR together with the analysis by secondary ion mass spectroscopy and single-crystal X-ray diffraction. The results indicate that when Ge dopant is lower than 1.0wt%, the FTIR spectroscopy is nearly the same as that of CZSi. With increasing Ge, the spectroscopy becomes complex in the lower wave number range. At the wave number of 7 10 cm(-1) a new peak appears, which is considered to be related to Ge dopant. The new peak of the spectroscopy becomes clearer with an increase in Ge, possibly due to the Ge-C or Si-Ge-C system. (C) 2004 Elsevier B.V. All rights reserved.