Temperature dependent angular dispersions of surface acoustic waves on GaAs

TL;DR

This study investigates how surface acoustic wave velocities on GaAs vary with temperature and crystal orientation, revealing parabolic trends and new slow modes at low temperatures, with implications for device design.

Contribution

It provides detailed measurements of temperature-dependent SAW velocities on GaAs and ZnO/GaAs, including the discovery of low-temperature slow modes and the use of ZnO films for efficient SAW generation.

Findings

Velocity decreases with temperature following a parabolic trend.

Slower SAW modes emerge at low temperatures on ZnO/GaAs substrates.

Velocity behavior varies with crystal orientation and substrate composition.

Abstract

We measure the phase velocities of surface acoustic waves (SAWs) propagating at different crystal orientations on (001)-cut GaAs substrates and their temperature dependance. We design and fabricate sets of interdigital transducers (IDTs) to induce 4 {\mu}m SAWs via the inverse piezoelectric (PZE) effect between the PZE [110] direction (set as {\theta} = 0{\deg}) and the non-PZE [100] direction ({\theta} = 45{\deg}) on GaAs. We also prepare ZnO film sputtered GaAs substrates in order to launch SAWs efficiently by IDTs even in the non-PZE direction. We quantify acoustic velocities between 1.4 and 300 K from the resonant frequencies in the S11 parameter using a network analyzer. We observe parabolic velocity-temperature trends at all {\theta}-values both on GaAs and ZnO/GaAs substrates. Below 200 K, in ZnO/GaAs substrates slower SAW modes appear around the [110] direction, which are unseen at RT.