Growth of ZnO films on (012)LiTaO3 by ECR-MBE and determination of their polarity

Single-crystal ZnO films were grown on (012)LiTaO₃ substrates by electron cyclotron resonance-assisted molecular beam epitaxy (ECR-assisted MBE). The film orientation differed with the ratio of oxygen to zinc. Under oxygen-rich conditions, (110)ZnO films with the c-axis parallel to the substrate surface were epitaxially grown. To identify the polarity of ZnO films with the c-axis parallel to the surface, a method using sideways chemical etching was proposed. The polarity of ZnO films was different when the films were grown on the + plane or the - plane of (012)LiTaO₃ substrates. For comparison, the polarity of ZnO films grown on r-plane sapphire was determined. As a result, it was found that the polarity of substrates greatly affected that of ZnO films. The ZnO/LiTaO₃ substrates offer a high electromechanical coupling factor of the shear horizontal-type leaky surface acoustic wave (SH-type leaky SAW) propagating along the X-axis due to an additional contribution of the piezoelectric shear effect of ZnO