Correlation of interference effects in photoreflectance spectra with GaAs homolayer thickness

Undoped GaAs epilayers grown by metalorganic chemical vapor deposition on Zn- and Si-doped GaAs substrates were studied using the technique of photoreflectance (PR) spectroscopy. Oscillations were observed in the PR spectra of the samples grown on n-type substrates below the fundamental band gap of GaAs. The origin of these oscillations was investigated in terms of interference between the light beam reflected from the air/film interface and the modulated beam reflected from the film/substrate interface. The latter is due to the modulation of the index of refraction of the substrate. The thickness of each film was calculated by a model which was used to fit the experimental spectra of the differential change in reflectance (ΔR/R) versus energy. The observed changes in the period of these oscillations as a function of film thickness were in good agreement with the calculated results. Scanning electron microscope measurements of the thicknesses of the films supported these calculations.