Solid phase reactions in Fe thin films on epi-Si0.8Ge0.2, poly-Si0.7Ge0.3, a-Si0.8Ge0.2, and a-Si0.7Ge0.3 layers on silicon have been investigated. The as-deposited samples were in situ annealed in the ultrahigh vacuum chamber at 400-800 degreesC for 30 min. The island structure was found to cause the abrupt increase in the sheet resistance of the annealed Fe/SiGe samples at 700 - 800 degreesC. The formation of FeSi islands containing a small amount of Ge is attributed to the preferential reactions of Fe with Si to Ge. As the annealing temperature was raised to 800 degreesC, the Fe(Si1-xGex) phase is the only phase found in the annealed Fe/epi-Si0.8Ge0.2 and Fe/poly-Si0.7Ge0.3 samples. On the other hand, at the annealing temperature above 700 degreesC, the beta-Fe(Si1-xGex)(2) phase was observed in the annealed Fe/a-Si0.8Ge0.2 and Fe/a-Si0.7Ge0.3 but the Fe(Si1-xGex) is still the dominant phase. The results indicate that the formation of Fe disilicide was retarded by the presence of Ge atoms. (C) 2004 Elsevier B.V. All rights reserved.