# Generation and propagation of super-high-frequency bulk acoustic wave in GaAs

## TL;DR

This study demonstrates the generation and propagation of super-high-frequency bulk acoustic waves in GaAs using piezoelectric resonators, revealing temperature-dependent absorption mechanisms and enabling high-quality acoustic devices for semiconductor control.

## Contribution

It introduces a method to generate and analyze 20 GHz acoustic waves in GaAs, showing their potential for high-frequency modulation of semiconductor properties.

## Key findings

- Intrinsic acoustic absorption in GaAs is dominated by phonon scattering at high temperatures.
- Absorption saturates at low temperatures due to boundary reflection losses.
- High-Q resonators with Bragg reflectors are feasible on GaAs nanostructures.

## Abstract

Coherent super-high-frequency (SHF) vibrations provide an excellent tool for the modulation and control of excitations in semiconductors. Here, we investigate the piezoelectric generation and propagation of longitudinal bulk acoustic waves (LBAWs) with frequencies up to 20 GHz in GaAs crystals using bulk acoustic wave resonators (BAWRs) based on piezoelectric thin ZnO films. We show that the electro-acoustic conversion efficiency of the BAWRs depends sensitively on the sputtering conditions of the ZnO films. The BAWRs were then used for the study of the propagation properties of the LBAWs in GaAs in the frequency and temperature ranges from 1 to 20 GHz and 10 and 300 K, respectively, which have so far not been experimentally accessed. We found that the intrinsic acoustic absorption of GaAs in the temperature range from 80 K to 300 K is dominated by scattering with thermal phonons. At lower temperatures, in contrast, the intrinsic acoustic absorption saturates at a frequency-dependent value. Experiments carried out with different propagation lengths indicate that the saturation is associated with losses during reflection at the sample boundaries. We also demonstrate devices with high quality factor fabricated on top of acoustic Bragg-reflectors. The results presented here prove the feasibility of high-quality acoustic resonators embedding GaAs-based nanostructures, thus opening the way for the modulation and control of their properties by electrically excited SHF LBAWs.