PL and XPS depth profiling of Si/Al 2O 3 co-sputtered films and evidence of the formation of silicon nanocrystals

Abstract

We have studied the correlation between light emission and structural properties of silicon nanocrystals formed in Al 2O 3 matrix by co-sputtering followed by an annealing in the temperature range of 900–1100 °C. X-ray diffraction (XRD) experiments revealed the nanocrystal formation which is a function of Si sputtering power and annealing temperature. The chemical structure and atomic compositions of Si, Al, O and their variations with depth from the sample surface have been investigated by X-ray photoelectron spectroscopy (XPS). Formation of Si nanocrystals is identified from the presence of Si–Si bonds whose strength increases with the annealing temperature. However, Si atoms resting in the region close to the surface of the sample is found to be oxidized. Photoluminescence (PL) spectroscopy is employed as a function of Si power, annealing temperature and sample depth. The origin of various PL peaks is discussed in terms of defect formation in Al 2O 3, emission from nanocrystals and interfaces. Defect related peaks are attributed to Cr 3+, Ti 3+ and F centers which are commonly observed in Al 2O 3. The emission from the Si nanocrystals is clearly identified in the wavelength range of 700–900 nm. The variation of this emission with the depth is in good correlation with the depth profile of Si–Si bonds as determined by the XPS analysis.