Reflectance Modulation by the Surface Field in GaAs

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Abstract
By studying reflectance spectra in GaAs modulated by a second, intense light beam, we have observed oscillatory structures in the spectra near the energy gap as well as near 3 eV. We conclude that these structures result from a neutralization of the builtin surface field by free carriers created by the intense light beam. The experimental line shape near the band gap is qualitatively very similar to the theoretical prediction for the Franz-Keldysh effect but is shifted to lower energies presumably due to exciton effects.