Spectroscopic ellipsometry study of GaAs/AlAs superlattices and Al0.5Ga0.5As alloy

We report the optical properties of a series of (GaAs)(n)(AlAs)(n) superlattices (SL) and the corresponding ternary alloy, Al0.5Ga0.5As, grown by Molecular Beam Epitaxy on the semi-insulating GaAs(011) substrates at 610 degrees C. The structural properties were confirmed by X-ray diffraction measurements. Spectroscopic ellipsometry (SE) measurements were performed to determine energies of the interband transitions at room temperature. For small SL periods (n < 5), the optical properties of the SLs are similar to those of the random alloy. As n increases, we found that the lower transition energies (below 4.0 eV) decrease from their alloy values. The results are compared with low temperature photoluminescence measurements. We also found a new structure at the lower E-2 peak, which is the best resolution of the E-2 structure in SL so far obtained by SE.