SPECTROSCOPY OF THE OPTICAL VIBRATIONAL MODES IN GAAS/ALXGA1-XAS HETEROSTRUCTURES WITH MONOLAYER-WIDE ALXGA1-XAS BARRIERS

摘要

We present the Raman and infrared spectra of GaAs/AlxGa1-xAs heterostructures with ultrathin (1 ML thick) AlxGa1-xAs barriers. The local-mode modification of a one-dimensional linear-chain model has been applied to analyze the measured optical vibrational modes. We demonstrate that the analysis based on the calculation of an effective confined length of vibrational modes in superlattices fails in the case of ultrathin barriers; the frequencies of confined modes should be rather calculated from microscopic considerations. Our calculations show the different damping of transverse and longitudinal GaAs optical phonons in a single monolayer barrier. The experimental results reveal the evidence of alteration of the symmetry of optical confined modes in superlattices with monolayer-wide barriers caused by the different arrangement of normal and inverted interfaces. The analysis of local modes originated from monolayer-wide barriers shows that the bonding of cation atoms in the monolayer-wide AlxGa1-xAs barriers differs from that in the bulk AlxGa1-xAs alloy and that more complicated bonding than the one used in a linear-chain model should be involved. [References: 22]