STUDY OF THE INTERNAL ELECTRIC-FIELDS ACROSS THE INTERFACES IN THE GAAS (1 A1,GA)AS MICROSTRUCTURES/

The electro-optical properties of MBE grown selectively doped GaAs/Al0 .3Ga0.7As heterostructures have been studied by photoreflectance spect roscopy. The spectra contained three types of oscillations in differen t spectra regions. The origins of different features in the spectra we re identified by comparing the spectra after different layers were etc hed off, and under external electric fields. There are two types of sp ectra oscillations above the energy gap of the GaAs. The one with a la rge oscillation period was due to the modulation of the internal elect ric field in the cap region and the one with a small period originated from the space-charge region near the back GaAs/Al0.3Ga0.7As interfac e, The lineshape oscillations above the energy gap of Al0.3Ga0.7As ori ginate from the undoped Al0.3Ga0.7As spacer. The internal electric fie lds were deduced from the spectra, and compared with the numerically c alculated results.