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

We present the Raman and infrared spectra of GaAs/AlxGa1-xAs heterostr uctures with ultrathin (1 ML thick) AlxGa1-xAs barriers. The local-mod e modification of a one-dimensional linear-chain model has been applie d to analyze the measured optical vibrational modes. We demonstrate th at the analysis based on the calculation of an effective confined leng th of vibrational modes in superlattices fails in the case of ultrathi n barriers; the frequencies of confined modes should be rather calcula ted from microscopic considerations. Our calculations show the differe nt damping of transverse and longitudinal GaAs optical phonons in a si ngle monolayer barrier. The experimental results reveal the evidence o f alteration of the symmetry of optical confined modes in superlattice s 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 i n 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.