AlGaAs/GaAs two-dimensional electron gas structures studied by photoreflectance spectroscopy

AlxGa1-x As/GaAS two-dimensional electron gas (2-DEG) heterostructures were fabricated by molecular beam epitaxy in three different laboratories. The samples were characterized by room temperature Photoreflectance (PR) spectroscopy and Hall measurements at 77 K. Internal electric fields were detected by the presence of Franz-Keldysh (FK) oscillations in the PR spectra. From a FK analysis we obtained the GaAs band-gap energy and the built-in electric field strength in each sample. On the other hand, in the energy region corresponding to AIxGa1-x As a broad PR signal was registered typical of a highly doped material. Using the third derivative theory we obtained the AlxGa1-xAs band-gap energy, and from this value the Al concentration in the samples. Results showed that the sample with highest electron mobility exhibited the lowest internal electric field strength.

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