Epitaxial Growth of ZnO Films on (0001) Sapphire at Low Temperatures by Electron Cyclotron Resonance-assisted Molecular Beam Epitaxy and Their Microstructural Characterizations

The details of epitaxial growth and microstructural characteristics of ZnO films grown on (0001) sapphire were investigated using X-ray diffraction (XRD), reflection high energy electron diffraction (RHEED), and plan-view and cross-sectional transmission electron microscopy (TEM). The films were grown by electron cyclotron resonance-assisted molecular beam epitaxy (ECR-assisted MBE). The ECR-assisted MBE was found to be capable of growing high quality epitaxial ZnO films at low temperatures in comparison with chemical vapor deposition (CVD) and RF sputtering. The films exhibited a high degree of epitaxy, a sharp interface between film and substrate, and a smooth surface morphology. The TEM observations revealed that the films were epitaxial with an orientational relationship of (0001)ZnO ∥(0001)Al_2O_3 and [1̄21̄0]ZnO ∥[1̄100] Al_2O_3. This is equivalent to a 30° rotation of ZnO relative to sapphire in (0001) plane.