Reflectance-difference spectroscopy study of the Fermi-level position of low-temperature-grown GaAs

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Abstract
The results of a reflectance-difference spectroscopy study of GaAs grown on (100) GaAs substrates by low-temperature molecular-beam epitaxy (LT-GaAs) are presented. In-plane optical anisotropy resonances which come from the linear electro-optic effect produced by the surface electric field are observed. The RDS line shape of the resonances clearly shows that the depletion region of LT-GaAs is indeed extremely narrow (≪200 Å). The surface potential is obtained from the RDS resonance amplitude without the knowledge of space-charge density. The change of the surface potential with post-growth annealing temperatures reflects a complicated movement of the Fermi level in LT-GaAs. The Fermi level still moves for samples annealed at above 600 °C, instead of being pinned to the As precipitates. This behavior can be explained by the dynamic properties of defects in the annealing process.

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