Measurements of acoustic properties of ZnO single crystals by the LFB/PW ultrasonic material characterization system

We evaluated the resistivities of a Z-cut ZnO single crystal plate specimen by measuring longitudinal-wave propagation characteristics (velocity and attenuation) in frequencies from 50 MHz to 1.5 GHz and also leaky surface acoustic wave (LSAW) velocities (V_LSAW) on the specimen surfaces at 225 MHz using a line-focus-beam/plane-wave (LFB/PW) ultrasonic material characterization (UMC) system. A slight decrease of V_LSAW was observed on -Z-plane of the specimen initially prepared in comparison with V_LSAW on the +Z surface. The corresponding Z-axis longitudinal-wave propagation characteristics exhibited significant velocity dispersion and frequency dependence of attenuation associated with relatively low resistivity. For the specimen by removing the -Z side surface by about 0.5-mm thickness, we observed the same high V_LSAW on both the ±Z surfaces. We could estimate the resistivities of 1·10⁴ ¿m for the specimen after removal of the 0.5-mm thick layer and 30 ¿m to 1·10⁴ ¿m distributed for the removed layer. This approach will contribute to establish our resistivity evaluation method using the LSAW propagation characteristics.