Oxidation of GeSi and applications

Citation

Liu, Wen-Shu (1994) Oxidation of GeSi and applications. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/pv5t-qy03. https://resolver.caltech.edu/CaltechETD:etd-11302007-084825

Abstract

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. The thermal oxidation of epitaxial and polycrystalline [...] has been studied in a dry or wet ambient at various temperatures. It is found that the composition of the resulting oxide depends on temperature, ambient, Ge content, structure of the [...] alloy, and the oxidation procedure. While in a wet ambient, and following the preheating procedure, a uniform [...] oxide is observed for a high Ge content at low oxidation temperatures, a [...] oxide is obtained for a low Ge content at high temperatures. A [...] oxide with reduced Ge content (y < x) is found in between. Ge piles up behind the oxide when [...] or [...] forms. When a uniform [...] 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. 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 [...] alloy. A model is proposed that is based on these three factors. The stability of an amorphous [...] in contact with an epitaxial (100)[...] layer obtained by partially oxidizing an epitaxial [...] layer on a (100)Si substrate in a wet ambient at 700°C has been investigated. It is noticed that [...] is thermodynamically unstable in contact with Si or GeSi, or in the presence of hydrogen and [...] will be reduced to elemental Ge. When [...] films are exposed to hydrogen, germanium nucleates homogeneously and the result is a suspension of nanocrystalline Ge grains embedded in a film of [...]. This nanocrystalline Ge is photoluminescent, as would be surmised by analogy with porous Si. When some parameters of the reduction experiment just described are altered, the outcome is radically different. This is accomplished by annealing a [...] bilayer on a Si substrate in a 5% [...] ambient. A heterogeneous nucleation occurs on the interface between the epitaxial [...] and the oxide, with the consequence that Ge grows in the form of an epitaxial layer there as it precipitates out of the oxide. Surprisingly, this Ge layer is of a superior crystalline quality than that of [...] seed layer on which it grows. Finally, we oxidized amorphous Ge/Si bilayers on Si substartes. Epitaxial [...] layers can be produced this way. Vacuum annealing of these samples only results in polycrystalline [...] layers.

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