Interference effects probed by photoreflectance spectroscopy

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Abstract
We report on oscillations in the photoreflectance (PR) spectra in the energy range below the band gap of GaAs on samples containing GaAs/AlGaAs quantum wells and the other multilayers grown on Si-doped GaAs substrates. The PR spectra with the quantum well chemically removed continue to show these oscillations, indicating that they are not related to the quantum well. These oscillations, which are probed by the modulation technique, are attributed to the interference effect of two light beams reflected from different interfaces of the sample. These spectra are calculated and good agreement with experimental data is obtained. We find that the interference effect distorts the line shape of the PR features associated with quantum wells and band edge of bulk semiconductors, especially at the low-energy side. Therefore, this effect must be taken into account during analysis. As an application, this interference effect can be used to accurately measure epilayer thicknesses.