Analysis of phase shifts due to etching in photoreflectance spectra of a GaAs/AlGaAs single-quantum well structure

Room-temperature photoreflectance measurements of a GaAs/Al0.2Ga0.8As single-quantum well structure showed well defined Franz–Keldysh oscillations in the neighborhood of the GaAs and Al0.2Ga0.8As band-edge energies. That experiment investigated the origin of the Franz–Keldysh oscillations by sequential etching and photoreflectance analysis of the grown layers and showed that the phase of the Franz–Keldysh oscillations shifted as the upper Al0.2Ga0.8As barrier was etched, with eventual phase reversal when roughly half of the upper barrier was removed. Here, these phase shifts are determined accurately using a novel Kramers–Kronig approach and they are interpreted in terms of optical interference effects using both a simple two-ray model and a multiple-reflection treatment incorporating a calculation of the Seraphin coefficients. The results also enable the thickness of the layers removed to be determined.