Abstract:

In addition to the well-known conventional acoustic wave propagation mode in three-dimensional solids, there exists the surface acoustic wave propagation mode where energy is only concentrated near the two-dimensional interface. In this work, utilizing the piezoelectric and inverse piezoelectric effects from GaAs substrates, we achieve the conversion between radiofrequency electromagnetic waves and surface acoustic waves with planar interdigital transducers, and successfully measure the surface acoustic wave velocity on a sample with a dimension of only 4 mm using superheterodyne-scheme lock-in technique, yielding a result of (2.9±0.1) km/s. We also fabricate a uniaxial stress cell with piezoelectric ceramics, capable of applying uniaxial strains up to approximately 10⁻⁴ to the sample, and observe the influence of strain on the surface acoustic wave velocity. We measure the surface acoustic wave velocity of the important semiconductor GaAs under stress, demonstrating the capability of this velocity measurement technique to probe the internal mechanical properties of solids in situ. The wave velocity measurements based on planar interdigital transducers overcome the macroscopic size requirements of traditional time-of-flight and standing wave methods. The superheterodyne-scheme lock-in technique established in this article has replaced the commercial vector network analyzers for measuring surface acoustic wave velocity, enabling possible future applications with low power input and high phase stability. As the measurement setup can also be used for experimental teaching related to solid-state physics, this work provides detailed parameters and fabrication processes for surface acoustic wave devices and homemade stress cell.

Key words: surface acoustic wave, uniaxial strain, uniaxial stress