Hypersound in simple one-dimensional device structures

Abstract

Brillouin spectroscopy, an inelastic laser light scattering technique capable of probing long wavelength acoustic phonons in a variety of material systems, was used to study hypersound in simple one-dimensional mesoporous silicon-based device structures formed using electrochemical etching methods. Brillouin spectra of porous silicon superlattices with binary periodicity on the order of the hypersound wavelength reveal zone folding, band gaps, and localized modes, indicating that these structures behave as hypersonic phononic crystals. Superlattices with smaller modulation wavelengths act as effective elastic media. New results on the behavior of hypersound in stacked superlattices and those with deliberately introduced defects will also be presented. Collectively, these studies have led to an improved fundamental understanding of classical wave behavior and interaction in low-dimensional systems and open up exciting opportunities for phonon engineering in a silicon-based platform.