Structure and light emission of Si-rich Al2O3 and Si-rich-SiO2 nanocomposites (original) (raw)
Related papers
2013
The present work deals with the comparative investigation of Si-ncs embedded in SiO 2 and Al 2 O 3 dielectrics grown by RF magnetron sputtering on fused quarts substrate. The effect of post-deposition processing on the evolution of microstructure of the films and their optic and luminescent properties was investigated. It was observed that photoluminescence (PL) spectra of Si x (SiO 2 ) 1-x films showed one PL band, which peak position shifts from 860 nm to 700 nm when the x decreases from 0.7 to 0.3. It is due to exciton recombination in Si-ncs. For Si x (Al 2 O 3 ) 1-x films, several PL bands peaked at about 570-600 nm and 700-750 nm and near-infrared tail or band peaked at about 800 nm were found. Two first PL bands were ascribed to different oxygendeficient defects of oxide host, whereas near-infrared PL component is due to exciton recombination in Si-ncs. The comparison of both types of the samples showed that the main radiative recombination channel in Si x (SiO 2 ) 1-x films is exciton recombination in Si-ncs, while in Si x (Al 2 O 3 ) 1-x films the recombination via defects prevails due to higher amount of interface defects in the Si x (Al 2 O 3 ) 1-x caused by stresses.
Nanoscale Research Letters, 2013
Silicon-rich Al 2 O 3 films (Si x (Al 2 O 3 ) 1−x ) were co-sputtered from two separate silicon and alumina targets onto a long silicon oxide substrate. The effects of different annealing treatments on the structure and light emission of the films versus x were investigated by means of spectroscopic ellipsometry, X-ray diffraction, micro-Raman scattering, and micro-photoluminescence (PL) methods. The formation of amorphous Si clusters upon the deposition process was found for the films with x ≥ 0.38. The annealing treatment of the films at 1,050°C to 1,150°C results in formation of Si nanocrystallites (Si-ncs). It was observed that their size depends on the type of this treatment. The conventional annealing at 1,150°C for 30 min of the samples with x = 0.5 to 0.68 leads to the formation of Si-ncs with the mean size of about 14 nm, whereas rapid thermal annealing of similar samples at 1,050°C for 1 min showed the presence of Si-ncs with sizes of about 5 nm. Two main broad PL bands were observed in the 500-to 900-nm spectral range with peak positions at 575 to 600 nm and 700 to 750 nm accompanied by near-infrared tail. The low-temperature measurement revealed that the intensity of the main PL band did not change with cooling contrary to the behavior expected for quantum confined Si-ncs. Based on the analysis of PL spectrum, it is supposed that the near-infrared PL component originates from the exciton recombination in the Si-ncs. However, the most intense emission in the visible spectral range is due to either defects in matrix or electron states at the Si-nc/matrix interface.
Defect-related luminescence of Si/SiO 2 layers
Journal of Physics: Condensed Matter, 2002
Photoluminescence (PL), photoluminescence excitation (PLE), and Raman spectra of Si-SiO x layers were measured as a function of Si content. Samples were prepared by co-sputtering of Si and SiO 2 and post-annealing. The average size of Si nanoparticles was estimated from Raman measurements. It was shown that, in general, the PL spectra consist of two bands with maxima in the 'red' and 'green' spectral ranges. The 'red' PL band is complex and contains two (IR and red (R)) components. The shift of the peak position of the IR component from 1.38 to 1.54 eV correlates with the decrease of the Si nanoparticle size from 5 to 2.7 nm. It was shown that this PL component could be ascribed to carrier recombination in silicon nanoparticles. The R component of the 'red' band as well as the 'green' band have similar dependences of the peak positions and intensities on the Si content and can be ascribed to defect-related luminescence. It was concluded that the light absorption in silicon nanocrystallites plays the main role in PLE process. Hot-carrier participation in the excitation of defectrelated bands was deduced.
Physics of The Solid State, 2009
Photoluminescence, infrared Fourier spectroscopy, Raman scattering, transmission electron microscopy, and electron diffraction were used to study the luminescent, optical, and structural properties of aluminum oxide layers (sapphire and films of Al2O3 deposited on silicon) implanted with Si+ to produce silicon nanocrystals. It is established that, in both cases, a high-temperature annealing of heavily implanted samples brings about the formation of silicon nanocrystals. However, the luminescent properties of the nanocrystals are strongly dependent on the type of pristine matrix; namely, nanocrystals in Al2O3 films emit light in the spectral range typical of Si quantum dots (700–850 nm), whereas in sapphire this photoluminescence is not observed. This difference is interpreted as being due to the fact that local stresses arise in the nanocrystal/sapphire system and break chemical bonds at the interface between the phases, whereas in Al2O3 films stresses are relaxed.
Nature of visible luminescence and its excitation in Si–SiOx systems
Journal of Luminescence, 2003
Photoluminescence (PL) spectra and their temperature dependence, as well as PL excitation and Raman spectra of Si-SiO x systems prepared by RF magnetron sputtering were investigated as a function of Si content. It was shown that PL spectrum of such systems consists of several bands. The correlation of shift of peak position of the lower-energy band from 1.38 to 1.54 eV with the change of size of Si nanocrystallites from 5 to 2.7 nm was observed. It was assumed that this PL band is connected with carrier recombination inside Si nanoparticles or with radiative transitions between a Si band and an interface level. It was shown that peak positions of the other observed bands (at 1.7, 2.06 and 2.32 eV) do not depend on the sizes of Si nanocrystallites. It was suggested that they are connected with silicon oxide defects based on the increase of intensities of these bands with increasing silicon oxide content. It was also shown that the excitation of PL is mainly due to light absorption in silicon nanocrystallites. Participation of hot carriers in excitation of defect-related bands was assumed. r
Si-rich-SiO(2) layers with high excess silicon content: light emission and structural properties
2008 International Conference on Luminescence and Optical Spectroscopy of Condensed Matter, 2009
Si-rich-SiO 2 layers with high excess Si content grown by radio-frequency magnetron sputtering were studied by Raman scattering, X-Ray diffraction, electron paramagnetic resonance, and photoluminescence methods. It was found that high temperature annealing stimulates the formation of Si crystallites with preferred orientation in <111> direction. It was shown that the effect of crystallites orientation depends on excess Si content. Besides, comparable contribution of amorphous and crystalline silicon phases in the structure was observed for the annealed layers with Si excess more than 55%. It was observed that both crystalline and amorphous Si inclusions give the essential contribution to the photoluminescence spectra.
Physica E: Low-dimensional Systems and Nanostructures, 2009
We have studied the correlation between light emission and structural properties of silicon nanocrystals formed in Al 2 O 3 matrix by co-sputtering followed by an annealing in the temperature range of 900-1100 1C. 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 2 O 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 2 O 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.
Electronic and optical properties of Al2O3/SiO2 thin films grown on Si substrate
Journal of Physics D: Applied Physics, 2010
The electronic and optical properties of Al2O3/SiO2 dielectric thin films grown on Si(1 0 0) by the atomic layer deposition method were studied by means of x-ray photoelectron spectroscopy and reflection electron energy loss spectroscopy (REELS). The band gaps of the Al2O3/SiO2 thin films before annealing and after annealing were 6.5 eV and 7.5 eV, respectively, and those of the γ-Al2O3 and α-Al2O3 phases were 7.1 eV and 8.4 eV, respectively. All of these were estimated from the onset values of the REELS spectra. The dielectric functions were determined by comparing the effective cross-section determined from experimental REELS with a rigorous model calculation based on dielectric response theory, using available software packages. The determined energy loss function obtained from the Al2O3/SiO2 thin films before annealing showed a broad peak at 22.7 eV, which moved to the γ-Al2O3 position at 24.3 eV after annealing. The optical properties were determined from the dielectric functio...