Focusing of surface-acoustic-wave fields on (100) GaAs surfaces

Focused surface-acoustic waves (SAWs) provide a way to reach intense acoustic fields for electro- and optoacoustic applications on semiconductors. We have investigated the focusing of SAWs by interdigital transducers (IDTs) deposited on (100)-oriented GaAs substrates. The focusing IDTs have curved fingers designed to account for the acoustic anisotropy of the substrate. Different factors that affect focusing, such as the aperture angle and the configuration of the IDT fingers, were systematically addressed. We show that the focusing performance can be considerably improved by appropriate choice of the IDT metal pads, which, under appropriate conditions, create an acoustic waveguide within the IDT. We demonstrate the generation of narrow (full width at half maximum of approx 15 mum), high-frequency (0.5 GHz), continuous SAW beams with vertical displacement as high as 4 nm collimated over distances that exceed 100 mum. (C) 2003 American Institute of Physics.