Effect of C on the thermal stability of an atomic layer of Si on Ge(1 0 0) was investigated during heat treatment between 500 and 700 degreesC. Because of the decrease of the Si coverage and the appearance of Ge hydride are observed after heat treatment at 500-700 degreesC, Si atoms deposited on Ge(1 0 0) tend to diffuse into the Ge layer. It is shown that an atomic layer of C suppresses the Si diffusion into Ge layer and a C containing Si atomic layer on Ge(1 0 0) is stable up to 600 degreesC. (C) 2003 Elsevier B.V. All rights reserved.