Importance of sample preheating in oxidation of Ge_xSi _1-x

Wet thermal oxidation at 1000°C of a 470-nm-thick epitaxial Ge _0.36Si_0.64 layer on (100)Si produces oxides of different composition depending on the details of the oxidation procedure. When a cold sample is directly exposed to the hot steam, the surface layer of the oxide contains both Ge and Si. Only SiO₂ forms if a preheated sample is exposed to the hot steam. The effect is not present for dry oxidation and is attributed to the known enhancement of the wet oxidation rate by Ge, coupled with the transient warm up of a sample when it is immersed cold in hot steam.