Abstract: A gas phase epitaxial deposition method deposits silicon, germanium, or silicon-germanium on a single-crystal semiconductor surface of a substrate. The substrate is placed in an epitaxy reactor swept by a carrier gas. The substrate temperature is controlled to increase to a first temperature value. Then, for a first time period, at least a first silicon precursor gas and/or a germanium precursor gas introduced. Then, the substrate temperature is decreased to a second temperature value. At the end of the first time period and during the temperature decrease, introduction of the first silicon precursor gas and/or the introduction of a second silicon precursor gas is maintained. The gases preferably have a partial pressure adapted to the formation of a silicon layer having a thickness smaller than 0.5 nm.