Tetrapod-Like ZnO Nanostructures Deposited on Si Substrates with AlN as Buffer Layer

Abstract

In this work, radio-frequency (RF) nitrogen plasma-assisted molecular beam epitaxy (PA-MBE) technique was used to grow AlN 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. The effect of annealing temperatures ranging from 600°C to 700°C in air for 1 h on the structural and optical properties of ZnO films is evaluated using X-ray diffraction (XRD) and room temperature photoluminescence (PL) spectroscopy. Tetrapod-like ZnO nanostructures were obtained from zinc granulated (99.99%) by thermal oxidation at 600°C in air for 1 h without any catalysts. The films show a polycrystalline hexagonal (wurtzite) structure without preferred (0002) orientation. The mean grain sizes are calculated to be about 22 nm and 50 nm for the ZnO films prepared at temperatures of 600°C and 700°C. The as-synthesized ZnO nanostructures were characterized by using scanning electron microscopy (SEM). Room temperature PL spectra of the ZnO films exhibit dominant excitonic ultraviolet (UV) emission and weak deep level visible emission. It is perceived that the ZnO film annealed at 600°C shows the strongest UV emission intensity among the temperatures ranges studied. From the ZnO film annealed at 600°C, the excellent UV emission is assigned to the good crystalline quality of the ZnO film and the low rate of formation of intrinsic defects.