X-Ray Standing Wave Analysis of GaAs/Si Interface

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The X-ray standing wave technique is applied to analyze initial structure of ultrathin GaAs/Si(111) and GaAs/Si(100) epitaxial layers grown by molecular beam epitaxy and metal-organic molecular beam epitaxy. We used two GaAs/Si(111) samples prepared with As adsorption and without As adsorption before GaAs growth, and one GaAs/Si(100) sample prepared under the same conditions as final GaAs layers being a single domain. Roughness and continuity of GaAs/Si interfaces were characterized using high resolution transmission micrographs before X-ray standing wave analysis. The sample with the initial Si(111)1×1 surface passivated by As atoms shows the same fluorescence profiles of Ga and As reported previously. When Ga was deposited first on the initial surface, however, fluorescence profiles suggested that about half of the interfacial Ga atoms are exchanged with As atoms, leaving both Si-Ga-As and Si-As-Ga bondings at the interface. The GaKα fluorescence profile of the GaAs/Si(100) sample showed a behavior similar to that of GaAs/Si(111) without As passivation. This suggests that double domain formation of GaAs is dominant at the initial stage of GaAs growth, even the final layer structure is a single domain. From the theoretical calculation, the ratios of these two domains at the initial stage are estimated to be about 0.4 and 0.6.