CHARACTERISTICS OF LOCALIZED ACOUSTIC MODES IN A N -LAYER-BASED SUPERLATTICE WITH DEFECT LAYERS

We present general expressions to calculate localized acoustic modes in a N-layer-based superlattice with defect layers by using a transfer-matrix method. Numerically, we investigate the properties of the localized modes in an AlAs-AlxGa1-xAs-GaAs superlattice with a defect layer AlyGa1-yAs. The influences of material and structural parameters on the localized modes are revealed with analyses. A comparison between the higher and lower branches of the localized modes is made. We show that the minigap and optimum localization are determined by the material and structural parameters of constituent layers in a unit cell as well as periodicity, while localized modes are dependent on both constituent and defect layers. Moreover, we find that the localized modes vary periodically with the width of the defect layer, and the number of branches of localized modes increases with the index of minigaps.