X-ray characterisation of zinc oxide (ZnO) single crystal substrates

Single crystal substrates of low defect density are paramount for fully realising the numerous applications of zinc oxide (ZnO) wide bandgap semiconductors. While ZnO substrates are commercially available from various vendors, very little information is available on the structural properties of these substrates. Therefore, an extensive evaluation of available substrates would serve as a basis for the development of ZnO based devices and technologies. In this study, bulk ZnO single crystal substrates grown by different growth techniques have been characterised using synchrotron white beam X-ray topography and high resolution X-ray diffraction. The substrates exhibit a wide range of dislocation densities from as high as 10⁶ cm ^-2 down to less than 1000 cm^-2 depending on the growth technique employed. The authors' evaluation reveals that ZnO crystals grown by the hydrothermal technique possess the best structural quality with dislocation densities of 800-1000 cm^-2 and rocking curves with a full width half maximum of less than 12 arc seconds.