We report photoreflectance-difference and reflectance-difference measurements on reconstructed GaAs (001) surfaces. From these data the linear and quadratic electro-optic coefficient spectra are determined in the important 2.8–3.4 eV spectral region. The surface strain and fields induced by the surface reconstruction are also determined. We show experimentally that between $c(4\times 4)$ and $(2\times 4)$ surfaces, there is an inversion of the surface electric field which we attribute to a direct piezo-electric effect related to the surface strain induced by reconstruction.

• Received 7 June 2005

DOI:https://doi.org/10.1103/PhysRevLett.96.047402