EN
We present a study of detailed line shapes of photoreflectance spectra for Al_{0.3}Ga_{0.7} As/SI-GaAs epitaxial layers grown by MBE. All measurements were performed at 80 K under UHV conditions with a special care for the samples surface quality. A set of the photoreflectance spectra was collected for photon energies close to the GaAs and Al_{0.3}Ga_{0.7}As band gaps (E_{0}). The photoreflectance spectra originated in the vicinity of the Al_{0.3}Ga_{0.7}As/SI-GaAs interface were analyzed using the complex Airy function model of Franz-Keldysh oscillations. To examine the effect of the epitaxial layer thickness on parameters characterizing the interface, a step-by-step chemical etching was applied for stripping the top layers. The built-in electric field intensity, field inhomogeneity and phenomenological broadening parameter for interface regions were determined as a function of the epilayer thickness.