Effect of Substrate Temperature on Structure and Composition of Si Nanocrystal-SiO~ x (original) (raw)
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Materials Science and Engineering: B, 2008
Si oxide films with a controlled excess of Si were deposited on Si wafers by LPCVD using Si 2 H 6 and 0 2 , thermally annealed to 1100°C for 1 h to form Si nanocrystals embedded in Si0 2 and subsequently annealed at 450 °C in forming gas. The samples were characterized by Fourier transform infrared spectroscopy, spectroscopic ellipsometry and cathodoluminescence spectroscopy. The excess of Si in the as-deposited samples, ranging from 0 to 70% in volume, was obtained from the ellipsometry data analysis. After annealing at 1100 °C, the samples show a luminescence band (peaking at 665 nm) at 80 K and at room temperature which is associated to the presence of Si nanocrystals. The growth rate, the excess of Si incorporated to the films and the intensity of the luminescence band were modelled using a Face-Centered Central Composite Design as a function of the main deposition variables (pressure, 185-300 mTorr; temperature, 250-400 °C; Si 2 H 6 /0 2 flow ratio, 2-5) aiming to control the growth process and the incorporation of Si in excess as well as to determine the experimental conditions that yield the samples with the maximum intensity of the luminescence emission.
Formation of luminescent Si nanocrystals by high-temperature rapid thermal chemical vapor deposition
Applied Physics Letters, 2003
We observe a completely different growth regime of silicon-rich oxide ͑SRO͒ layers by rapid thermal chemical vapor deposition for the formation of luminescent nanocrystals. The growth regime is characterized by low ͓N 2 O͔/͓SiH 4 ͔ ratios ͑Ͻ1͒ and high growth temperatures ͑Ͼ700°C͒. High-resolution cross-sectional transmission electron microscopy ͑XTEM͒ shows the bimodal distribution of large polycrystals and nanocrystals after post-deposition annealing. The luminescence is attributed to the nanocrystals. Fourier transform infrared spectroscopy in conjunction with XTEM and energy-dispersive x-ray studies show the phase separation and bonding reconfiguration in as-deposited SRO layers. The effectively increased oxygen content in the oxide matrix by phase separation and bonding reconfiguration reduces the diffusion coefficient of Si in the matrix, resulting in the formation of nanocrystals during post-deposition annealing.
Journal of Applied Physics, 2010
SiO x / Si-nanocrystals ͑Si NCs͒ heterolayers were fabricated employing a rf magnetron sputtering system. The synthesis process, through modification of the oxygen partial pressure of the plasma, promotes the synthesis of stoichiometric SiO 2 layers and affect the Si NCs layer giving place to SiO x / Si NCs ͑1.64Ͻ x Ͻ 2͒ interfaces. All as-grown samples showed strong photoluminescence ͑PL͒ bands in the visible and near-infrared regions; transmission electron microscopy measurements confirmed the presence of Si NCs. Thermal annealing at 1100°C promoted the SiO 2 stoichiometry in the interface and the crystallization of more Si NCs. The results allow us to clearly identify the origin of the PL bands; indicating that the near-infrared emission is related to the nonstoichiometric oxide while the red and green bands are originated in Si NCs.
Photoluminescence in Si/ZnO nanocomposites
Materials Science and Engineering: B, 2004
Composite films of Si and ZnO were prepared by r.f. co-sputtering technique with different Si contents. Photoluminescence (PL) and Raman spectroscopy were used to characterize the films. Transmission electron microscopy revealed that the Si dispersed in the ZnO matrix form nano-particles of size ranging from 2 to 4 nm. On thermal annealing at and above 700 • C, the nano-particles aggregated to form micro-crystals. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy revealed that the Si in the composite films remain in the SiO X (0 < X < 2) state. With the increase of annealing temperature, the higher oxidation state of Si is revealed. A strong and broad PL peak revealed at around 2.24 eV along with the other emissions. The emission could involve a band-to-band recombination mechanism within Si cores and emission sensitive to surface and/or interface states. Evolution of PL emissions and Raman peaks are discussed on the basis of formation of nano-particles and micro-crystals in the films and variation of oxidation state of Si with annealing temperature.
We report on efficient ZnO nanocrystal (ZnO-NC) emission in the near-UV region. We show that luminescence from ZnO nanocrystals embedded in a SiO2 matrix can vary significantly as a function of the annealing temperature from 450°C to 700°C. We manage to correlate the emission of the ZnO nanocrystals embedded in SiO2 thin films with transmission electron microscopy images in order to optimize the fabrication process. Emission can be explained using two main contributions, near-band-edge emission (UV range) and defect-related emissions (visible). Both contributions over 500°C are found to be size dependent in intensity due to a decrease of the absorption cross section. For the smallest-size nanocrystals, UV emission can only be accounted for using a blueshifted UV contribution as compared to the ZnO band gap. In order to further optimize the emission properties, we have studied different annealing atmospheres under oxygen and under argon gas. We conclude that a softer annealing temperature at 450°C but with longer annealing time under oxygen is the most preferable scenario in order to improve near-UV emission of the ZnO nanocrystals embedded in an SiO2 matrix.
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
Characterization of ZnO:Si nanocomposite films grown by thermal evaporation
Physics Letters A, 2008
Nanocomposite thin films of Zinc Oxide and Silicon were grown by co-evaporating powdered ZnO and Si. This resulted in nanocrystallites of ZnO being embedded in Silicon. The mismatch in crystal structures of constituent materials result in the ZnO nanocrystals to exist in a state of stress. This along with oxygen vacancies in the samples result in good Photoluminescence emission at 520nm. Also, Silicon background gave a photoluminescence emission at 620nm. The structure was found quite stable over time since the homgenously dispersed ZnO nanocrystals do not agglomerate. The nanocomposites promises to be a useful candidate for future optoelectronic devices.
IOP Conference Series: Materials Science and Engineering, 2015
Zinc oxide (ZnO) thin films were prepared using reactive RF magnetron sputtering of a pure metallic zinc target onto n-type (100) silicon substrates. The evolution of the surface morphology and the optical properties of the films were studied as a function of the substrate temperature, which was varied from ambient to 300 o C. X-ray diffraction pattern of ZnO thin film shows the appearance of c-axis oriented (002) peak for all samples shows varying degrees of crystallinity of films. Photoluminescence studies were also carried out (350-700 nm) to study the crystallinity and optically active defects in the films. PL spectra of the film shows UV emission peak depicts good crystallinity of ZnO film where as the intensity of deep level emission band decreases with increase in substrate temperature due to the formation of stoichiometric ZnO film which causes decrease in defect.