Acoustic waves in finite superlattices: Influence of buffer layers

摘要

The influence of buffer layers on acoustic waves of shear horizontal polarization in finite superlattices is investigated here theoretically. Using a Green's-function method, we have obtained closed-form expressions of local and total densities of states as a function of the frequency omega and the wave vector k(parallel to) parallel to the layers. The expressions of the phonon trapping times are also derived and compared to the density of states. Due to the substrate/buffer layer/superlattice interaction, different kind's of localized and resonant discrete modes are found and their properties are investigated. In particular, we show the possibility of finding well-defined guided modes in the buffer layer or in the superlattice depending on whether the velocity of the transverse acoustic waves in the buffer is lower or higher than those in the superlattice and the substrate, respectively. These modes appear as well-defined peaks of the density of states and trapping times. Specific applications of our analytical results are given in this paper for a GaAs (Si) buffer layer embedded between a Si (GaAs) substrate and a finite GaAs-AlAs superlattice. [S0163-1829(99)13003-0]. [References: 48]