RHEED patterns from the -plane sapphire substrate after the thermal cleaning for the azimuths of (a)  and (b) . RHEED patterns from the ZnO films grown at different growth temperatures on the sapphire substrate with azimuths of (a) and (b) were displayed in (c) and (d), respectively. The azimuths of ZnO films determined based on the pattern from the film grown at were mentioned in (c) and (d). The white arrows indicate the extra spots.
XRD curves for the ZnO films grown at a temperature range of with an interval of . The position of diffraction peaks for bulk ZnO is mentioned by the vertical line.
Plots of the peak intensity ratio of (a) reflections and (b) ZnO reflections.
FWHMs XRCs for the on-axis reflection and off-axis reflection for the ZnO films grown at different growth temperatures between 200 and . In the case of the on-axis XRCs, measurements were performed under different angles ( and 90°), where the (90°) represents that the ⟨0001⟩ direction of the ZnO is parallel (perpendicular) to the axis.
(a) AFM images ( scan area) for the ZnO films with different growth temperatures between 200 and . The arrow marked on the images indicates the ZnO ⟨0001⟩ direction. (b) rms roughness values measured from (a).
(a) Cross-sectional bright field TEM micrograph at the ZnO/sapphire interface and (b) corresponding SAED pattern. The zone axes of ZnO and are ZnO  and .
(a) Cross-sectional bright field TEM micrograph taken along the ZnO  zone axis showing the ZnO inclusion with different planes from the surrounding -plane. Note that the inclusion was not nucleated at the interface and reached the surface of the ZnO film. (b) Cross-sectional HRTEM micrograph for the inclusion surrounded by -plane ZnO taken along the ZnO zone axis. (c) Digital diffraction patterns are obtained by fast Fourier transform from the marked square regions in (b). Index for the diffracted spots is given.
FWHMs (in degree) of the various ZnO peaks appeared in Fig. 2.
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