Chemical Structure of As-Stabilized Surface during GaAs Metalorganic Vapor Phase Epitaxy Studied by Surface Photo-Absorption

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Abstract
As-stabilized surface structures during GaAs metalorganic vapor phase epitaxy (MOVPE) are investigated by taking a difference in surface photo-absorption spectrum between two principal axes, which produces the surface anisotropic spectra mainly due to As dimers on the surface. We established the surface phase diagram as a function of substrate temperature and AsH3partial pressure. Below 630° C, independently of AsH3partial pressure, the surface isc(4×4)-like whose As dimers have a bond axis parallel to [110]. As the substrate temperature increases and the AsH3partial pressure decreases, the surface evolves to (2×4)γ-like which contains As dimers having a bond axis parallel to [1̄10]. At a substrate temperature of around 600° C, a phase diagram comparison between MOVPE and molecular beam epitaxy (MBE) shows that thec(4×4)-like surface is stable in MOVPE, while the (2×4) surface is stable in MBE. The characterization of step structure by atomic force microscopy shows that the difference of As structures has a significant effect on the step straightening mechanism.