Modelling and analysis of photoreflectance spectra of GaAs/AlGaAs single-quantum-well structures

Results are presented for room-temperature photoreflectance measurements on four GaAs/AlxGa1-xAs single-quantum-well structures, with x=0.2 and x=0.3, and nominal GaAs quantum well widths of 50 AA and 100 AA. However, the photoreflectance spectra of all the samples display pronounced Franz-Keldysh oscillations in the neighbourhood of both the GaAs and AlxGa1-xAs band edge energies which overlap with, and partially obscure, the photoreflectance features from the quantum well. The spectra are fitted with a model incorporating an approximate lineshape form for the Franz-Keldysh oscillations together with third-derivative functional forms. This has enabled the single-quantum-well transition energies to be determined as well as the DC electric field responsible for the Franz-Keldysh oscillations. In order to identify these transitions, the results are compared with a theoretical model for the single-quantum-well structures, which incorporates parabolic effective masses, and good agreement is obtained.