Determination of crystallographic polarity of ZnO bulk crystals and epilayers

The crystallographic polarity of ZnO bulk crystals and epilayers were determined by X-ray diffraction (XRD) using anomalous dispersion near the Zn K-edge. The method is not destructive and is straightforward to carry out using a typical XRD measurement system. The polarity difference between the Zn (0001) and O (000 1̄) surfaces could be easily determined using a {0002} diffraction peak and the Bremstrahlung radiation from a Cu rotating anode source. By using the normalized pre and post-Zn K-edge diffraction intensity ratios of the {0002} diffraction peak, Zn polar and O polar ZnO layers could always be distinguished but, the absolute value of the ratio was found to change with layer thickness. Acid etching results confirmed the veracity of the polarity determination of the XRD measurement. To test the technique, Zn and O polar ZnO layers were grown by radical source molecular beam epitaxy on MgO buffer layers on c-sapphire substrate and O polar ZnO layers were grown on a-plane substrates and measured using the X-ray technique with excellent agreement.