Abstract
The thermal oxidation of polycrystalline GexSi1−x (0.10≤x≤0.47) and pseudomorphic Ge0.2Si0.8 has been studied in wet ambient at 550 to 900 °C. A uniform GexSi1−xO2 oxide is observed by backscattering spectrometry for a high Ge content at low oxidation temperatures; a SiO2 oxide is obtained for a low Ge content at high temperatures; a GeySi1−yO2 oxide with reduced Ge content (y<x) is found in between. Ge piles up behind the oxide when SiO2 or GeySi1−yO2 form. The transition between these three types of oxides also depends on the crystallinity of the GeSi alloy. When a uniform GexSi1−xO2 oxide grows, its thickness is proportional to the square root of the oxidation duration, which indicates that the rate-limiting process is the diffusive transport across the oxide of, most probably, the oxidant. The rate increases with the Ge content in the alloys. The proportionality constant, B, for this process is B(T)=[(1.0±0.2)×1011 nm2/h]exp[(−1.1±0.2 eV)/kT] for Ge0.47Si0.53. It is proposed that, in general, the oxidation behavior is determined by the competition between the speed of the diffusive process in the unoxidized GeSi alloy and the velocity at which the oxidation front progresses. The controlling factors are the oxidation temperature, the composition, and the structure of the GexSi1−x alloy. A model is proposed that is based on these three factors. Analogies with this system exist where all three elements are solid.
Published Version
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