Polarized Raman spectroscopy and X-ray diffuse scattering in InGaAs/GaAs(100) quantum-dot chains

Using polarized Raman spectroscopy and high resolution X-ray diffraction we have investigated self-organized In_0.45Ga_0.55As quantum-dot chains in InGaAs/GaAs multilayer structures. It is shown that the formation of InGaAs QDs in InGaAs/GaAs multilayered structures is accompanied by a strong improvement in the uniformity of size and shapes of QDs as well as vertical alignment and lateral ordering. At mean densities, extended chains of QDs (up to 5 μm) appear along the $ 1\bar 10] $ direction; however, increased ordering of QDs along the 110] direction could be observed, too. For the first time, InGaAs dot-chains were investigated using polarized Raman scattering. Observation of optical phonons localized in InGaAs QDs and two-dimensional (2D) layers is demonstrated. An obvious anisotropy in the intensity of Raman modes was observed when the electric field vector of the exciting laser beam is parallel or perpendicular to the wire-like axis $ 1\bar 10] $ of dot-chains. This effect may be related to symmetry lowering effects and real anisotropic geometry of the QDs and 2D wetting layers.