The temperature and doping-concentration dependence of the oscillatory properties in the photoreflectance (PR) spectra of GaAs grown by molecular-beam epitaxy has been studied in detail. The peak separation of the oscillatory part of the PR spectrum is related to the internal electric field in the sample. Both the peak spacing of the oscillations and the internal electric field increase with increasing temperature and doping density. A PR spectrum with two kinds of oscillations from two interfaces across different doping profiles was also observed. Our study of oscillatory properties not only verified the electromodulation character of the PR experiment but also extracted the temperature dependence of the surface Fermi level.
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