Resumen

Título: Photoreflectance spectroscopy of AlGaAs/GaAs heterostructures with a two-dimensional electrón gas system.
Resumen: We report a study of AlGaAs/GaAs semiconductor heterostructures with a two-dimensional electron gas system grown under different conditions by molecular beam epitaxy in three different laboratories. We performed photoreflectance (PR) measurements of this set of samples and analyzed the Franz–Keldysh oscillations associated with the E0 transition of GaAs. We found that the sample with the highest electron mobility, as observed in Hall measurements at 77 K exhibited the lowest electric field strength. In addition, the 12 K photoluminescence (PL) spectra of the samples revealed intense and narrow free exciton luminescence in the sample with the highest electron mobility, while samples with lower mobility values showed impurities related PL lines. It is suggested that the electron mobility is affected by unintentional C impurities, which act like dispersion centers in the 2-DEG and increase the internal electric fields in the GaAs region. On the other hand, the PR spectra close to the AlGaAs band-gap energy region presented broad PR signals, due to the Si-doping in the alloy. The sample with the highest quality presented the most intense AlGaAs PR signal. We believe that low AlGaAs PR signal intensities are caused by unintentional incorporation of impurities during the preparation of the samples, which degrade the optical properties of the alloy. ©2002 American Vacuum Society.
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