Heavy C atomic-layer doping of about 10(14)cm(-2) at the heterointerface between Si1- xGex and Si using an ultraclean low-pressure chemical vapor deposition has been investigated. By heavy C atomic-layer doping at heterointerface between a Si cap layer and a Si0.55Ge0.45 layer in Si/Si0.55Ge0.45/Si(100) heterostructure, the intermixing between Si and Ge at heterointerface is effectively suppressed. For 4 run thick Si0.55Ge0.45 cap layer/Si(100) heterostructure with C atomic-layer doping, Ge fraction of (0.45) and strain scarcely change with the heat treatment at 750 degrees C, while those without C atomic-layer doping are reduced. For 40 nm thick Si0.55Ge0.45 cap layer/Si(100) heterostructure, whose Si0.55Ge0.45 thickness is close to the critical thickness, it is found that the strained Si0.55Ge0.45 cap layer is relaxed by C atomic-layer doping at heterointerface. These results suggest that the heavy C atomic-layer doping suppresses strain relaxation as well as intermixing between Si and Ge at the Si-1 (-) Ge-x(x)/Si heterointerface especially for the heterostructure composed of nm-order thick films. (C) 2009 Elsevier B.V. All rights reserved.