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)Al2O3 and [(1) over bar 2 (1) over bar 0]ZnO \\ [(1) over bar 100]Al2O3. This is equivalent to a 30 degrees rotation of ZnO relative to sapphire in (0001) plane.