Fabrication and characterization of ZnO nanostructures on Si (111) substrate using a thin ALN buffer layer

In the present work, radio-frequency (RF) nitrogen plasma-assisted molecular beam epitaxy (PA-MBE) technique was used to grow AlN thin layers on Si(111) substrate. Subsequently, the thermal evaporation technique was used to deposit the zinc films on Si(111) substrates with AlN as buffer layer. ZnO nanostructures were obtained from zinc granulated (99.99%) by thermal oxidation from 400 °C to 600 °C in air for 1 hours without any catalysts. The effect of annealing temperatures were studied ranging from 400 °C to 600 °C in air for 1 hours. The AlN was introduced to accommodate the lattice mismatch and thermal expansion mismatch between ZnO layer and Si substrate. The structural and optical properties of ZnO nanostructures are studied through scanning electron microscopy (SEM), X-ray diffraction (XRD) and room temperature photoluminescence (PL) spectroscopy. The films show a polycrystalline hexagonal wurtzite structure without preferred (0002) orientation. The mean grain sizes are calculated to be about 18 nm, 22 nm and 50 nm for the ZnO films prepared at temperatures of 400 °C, 500 °C and 600 °C. The structure of the fabricated nanomaterials were characterized by scanning electron microscopy (SEM). The PL spectra of the ZnO nanostructures having a sharp excitonic ultraviolet (UV) emission and very weak defect-related deep level visible emissions. It is showed that the ZnO nanostructures thermal annealed treatment was performed at 600 °C shows the strongest UV emission intensity among the temperatures ranges studied. In addition, from the one-dimensional ZnO nanostructures thermal annealed at 600 °C, the stronger UV emission is assigned to the best crystalline quality of the ZnO film