OPTICAL ANISOTROPY IN GAAS/ALAS(110) SUPERLATTICES

Short-period GaAs/AlAs superlattices grown along the [110] direction have orthorhombic symmetry and thus exhibit two different dielectric functions epsilon(omega) along the main axes perpendicular to the growth direction ([001] and [110BAR] direction). Spectroscopic ellipsometry as well as ab initio calculations have been used to determine the optical properties of these superlattices. The E1 transitions split into two components with different strengths for the two principal polarizations. This effect can be qualitatively interpreted on the basis of a k.p model for the E1 transitions and confinement arguments. The E2 transition for [001] polarization is lower in energy than the one for [110BAR] polarization. In addition, we observe a transition slightly above E2, which occurs predominantly in [001] polarization. Two other structures specific to the superlattices are identified, in analogy to the case GaAs/AlAs superlattices grown along [001]. Confinement effects on optical transitions for various superlattice periods are also discussed.