Franz-Keldysh and band-filling effects in the electroreflectance of highly dopedp-type GaAs

The electroreflectance of highly doped semiconductors has been modeled in terms of the Franz-Keldysh effect and the band-filling (Moss-Burstein) effect, including the spatial variation of the modulation. Calculations are compared to experimental electrolyte electroreflectance results obtained from 2×${10}^{18}$ ${\mathrm{cm}}^{\mathrm{-}3}$ p-type GaAs electrodes in a dilute sulfuric-acid electrolyte. The form of the experimental line-shape variation with applied potential is successfully predicted, although it appears that only about a third of any change in dc potential applied to the electrode is actually dropped across the semiconductor space-charge region in samples of this dopant density. The relative significance of the Franz-Keldysh and Moss-Burstein effects is discussed in light of the possibility of band-gap narrowing.