Abstract
The electronic structure of several n-type GaAs samples containing ‘‘δ-doping’’ layers of Si have been studied using photoreflectance (PR) spectroscopy. Well-defined oscillatory features due to electronic transitions well above the band gap are observed at 300 K and identified as Franz–Keldysh oscillations. The energy spacing and the intensity of the oscillations decrease with decreasing temperature as a consequence, we believe, of changes in the electric field due to the surface charges. Self-consistent energy-band calculations support the interpretation that the oscillatory structure is due to Franz–Keldysh effects. The imposition of magnetic fields up to 15 even at room temperature has a pronounced influence on the PR spectrum. Parallel fields suppress the oscillatory structure but cause a large increase in the PR peaks near the GaAs energy gap. At 4.2 K Landau-like spectral features are observed for fields applied perpendicular to the doping layer.
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