2ATR Adaptive Communications Research Laboratories.

The modification of the optical properties of semiconductors applying external electric fiels has been known for a while. In fact, in III-V heterostructure based quantum systems the quantum confined Stark effect (QCSE) has been showed, here the quantum well (QW) excitonic transitions are modified by the influence of an electric field. Most of the work in this direction has been carried out employing heterostructures grown on GaAs(100) substrates. The advance in the development of growing techniques such as molecular beam epitaxy has promoted the research in QWs heterostructures grown on substrate orientations with high piezoelectric coefficients such as GaAs(111) and GaAs(311). The main attraction of these orientations is to employ their built-in electric fields to produce the QCSE. However, a clear understanding of the effect of the built-in electric fields on the QW excitonic states is very important to any possible application. In this work we report results of the optical characterization of GaAs/In_1-xGa_xAs/GaAs QWs grown by MBE on (100), (111) and (311) GaAs substrates employing photoluminescence (PL), photoreflectance (PR) and PR subjected to the action of an uniform external field. PL spectroscopy through the line full width at half maximum, give us information about the structural quality and interface sharpness of the QWs. Besides of the room temperature direct identification of the confined excitonic transitions energies, PR permitted us to evaluate the strength of an effective internal electric field through the analysis of the Franz-Keldysh oscillations.