Annealing Effect on a (0001)-Oriented ZnO Single-Crystal Bulk-Acoustic-Wave X-Ray Detector

This work demonstrates a ZnO single-crystal bulk-acoustic-wave (BAW) nuclear radiation detector based on piezoelectricity-photoconductivity interactions, which is suitable for developing a frequency-domain multiplexing system for cosmic X-ray and γ-ray observations. The nuclear radiation-generated photocarriers in ZnO crystals screen the piezoelectric charge and reduce the acoustic velocity, inducing a negative resonant frequency shift for the detector. (0001)-oriented ZnO single crystals are used to fabricate high-quality BAW detectors. Unannealed and annealed crystal detectors are compared, and the annealed detector is found to show a higher signal-to-noise ratio and faster response speed due to a higher quality factor and fewer defects. The annealed ZnO crystal shows a resistivity of 1011 Ω cm, a high electromechanical coupling factor of 10.4%, and a high quality factor of 500. The annealed detector also shows a linear X-ray response with a responsivity of 0.89 k/Gy for an X-ray tube voltage of 70 kV, indicating great potential for application of bulk single-crystal-based BAW detectors in the field of nuclear radiation detection.