RETRACTED: Absorption spectra of nanocrystalline silicon embedded in SiO2 matrix (original) (raw)
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Absorption spectra of nanocrystalline silicon embedded in SiO[sub 2] matrix
Applied Physics Letters, 1999
. Nanocrystalline silicon nc-Si embedded SiO matrix has been formed by annealing the SiO films fabricated by 2 x Ž . plasma-enhanced chemical vapor deposition PECVD technique. Absorption coefficient and photoluminescence of the films have been measured at room temperature. The experimental results show that there is an ''aUrbach-like''b exponential Ž . 1r2 Ž . absorption in the spectral range of 2.0-3.0 eV. The relationship of a hn A hn y E demonstrates that the luminescent g nc-Si have an indirect band structure. The existence of Stokes shift between photoluminescence and absorption edge indicates that radiative combination can take place not only between electron states and hole states but also between shallow trap states of electrons and holes. q
Absorption spectra of nanocrystalline silicon embedded in SiO2 matrix
Applied Physics Letters, 1999
Nanocrystalline silicon embedded SiO2 matrix is formed by annealing the SiOx films fabricated by plasma enhanced chemical vapor deposition technique. Absorption coefficient and photoluminescence of the films have been measured at room temperature. The experimental results show that there exists an exponential absorption in the spectral range of 2.0-3.0 eV. The relationship of (αhν)1/2∝(hν-Eg) demonstrates that the luminescent nanocrystalline silicon has an indirect band structure. The existence of Stokes shift between photoluminescence and absorption edge indicates that radiative combination can take place not only between shallow trap states of electrons and holes but also between quantized states of electrons and holes.
Optical properties of nanocrystalline silicon embedded in SiO 2
Science China-mathematics, 1999
Nanocrystalline silicon embedded SiO2 matrix has been formed by annealing the a-SiOx films fabricated by plasma enhanced chemical vapor deposition technique. Absorption and photoluminescence spectra of the films have been studied in conjunction with micro-Raman scattering spectra. It is found that absorption presents an exponential dependence of absorption coefficient to photon energy in the range of 1.5–3.0 eV, and a sub-band appears in the range of 1.0–1.5 eV. The exponential absorption is due to the indirect band-to-band transition of electrons in silicon nanocrys-tallites, while the sub-band absorption is ascribed to transitions between surfaces and/or defect states of the silicon nanocrystallites. The existence of Stokes shift between absorption and photoluminescence suggests that the phonon-assisted luminescence would be enhanced due to the quantum confinement effects.
Photoluminescent properties of nc-Si/SiO x nanosystems
Applied Nanoscience, 2018
In this work the nc-Si/SiO x nanosystems were obtained on the silicon substrate by means of evaporation of silicon powder in an oxidizing atmosphere. Then deposited SiO x films were irradiated from 226 Ra isotope and were annealed at 1000 °C to grow nc-Si. By means of the ellipsometric technique we studied the effect of annealing duration and irradiation on the optical characteristics of nc-Si/SiO x films. It was found that irradiation of obtained films promotes visible photoluminescence witdh maximum near 740 nm. More effective photon emission is caused by the change of nc-Si passivation conditions. Obtained experimental and theoretical results show the important influence of the Si/SiO x interface on the light emitting properties of nc-Si.
Variation of photoluminescence from Si nanostructures in SiO2 matrix with Si+ post implantation
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2007
Si nanoclusters were formed by 28 Si ion implantation into SiO 2 matrix and subsequently annealed at 1050°C for 2 h under N 2 ambient. The photoluminescence (PL) characteristics depend on the 28 Si fluence. The PL signals seen at around 775 nm and 825 nm are assigned to light emitting centers connected to formation of Si clusters, for 5 · 10 16 cm À2 and 1 · 10 17 cm À2 28 Si fluences, respectively. Defect-related light emission observed at around 625 nm emerges only in the case of high implantation fluence. These sample sets were post implanted with 28 Si ions at fluences between 1 · 10 12 and 1 · 10 14 cm À2 to monitor the variations in PL emission as a function of post implantation fluence. The PL emission decreases and exhibits a blue-shift with increasing post implantation fluence and quenches totally when the fluence exceeds a certain value, while the peak seen at 625 nm which is related to matrix defects is enhanced after the post implantation. Upon thermal annealing, the PL peaks measured at 775 nm and 825 nm recovered and reached the intensity of the peak before the post implantation. The variations in the PL peak with the implantation fluence and annealing conditions are ascribed to the different structure of Si nanoinclusions in the SiO 2 matrix.
A novel method for the fabrication of nanometer-sized Si crystals in an amorphous SiO2 matrix by ion implantation and thermal processing is reported. Transmission electron microscopy indicates the formation of Si nanocrystais by annealing at 1 100 "t2, and the growth in average size of Si nanocrystals with increasing annealing time. The shape of the emission spectrum of the photoluminescence is found to be independent of both excitation energy and annealing time, while the excitation spectrum of photoluminescence increases as the photon energy increases and its shape depends on annealing time. The results indicate that the photons are absorbed by Si nanocrystals, for which the bandgap energy is modified by the quantum confinement effects, and the emission of photons is not due to direct electron-hole recombination inside Si nanocrystals but is related to defects probably at the interface between Si nanocrystals and SiO2. This method is fully compatible with silicon microelectronic technology.
Journal of Applied Physics, 2007
Si nanocrystals ͑nc-Si͒ with different sizes embedded in SiO 2 matrix have been synthesized with various recipes of Si ion implantation. The influence of nanocrystal size on optical properties, including dielectric functions and optical constants, of the nc-Si has been investigated with spectroscopic ellipsometry. The optical properties of the nc-Si are found to be well described by the four-term Forouhi-Bloomer model. A strong dependence of the dielectric functions and optical constants on the nc-Si size is observed. For the imaginary part of the dielectric functions, the magnitude of the main peaks at the transition energies E 1 and E 2 exhibits a large reduction and a significant redshift in E 2 depending on the nc-Si size. A band gap expansion is observed when the nc-Si size is reduced. The band gap expansion with the reduction of nc-Si size is in good agreement with the prediction of first-principles calculations based on quantum confinement.
Formation of and Light Emission from Si Nanocrystals Embedded in Amorphous Silicon Oxides
ECS Transactions, 2006
The formation of Si-nc embedded in amorphous Si oxides promoted by thermal annealing of Si y O 1-y films (y=0.34-0.45) fabricated by plasma enhanced chemical vapor deposition is examined by X-ray diffraction and electron microscopy. UV and synchrotron radiation excited photoluminescence from the obtained structures is also studied and its origin elucidated.
Physics of the Solid State, 2012
A comprehensive comparative study of SiO 2 and Al 2 O 3 oxide layers with Si nanocrystals formed by Si + ion implantation and high temperature annealing has been performed. Information on morphology, phase composition, structure, and luminescent properties of ensembles of ion synthesized silicon nanocrys tals has been obtained using confocal Raman microscopy, X ray diffraction, Fourier transform infrared spec troscopy, electron paramagnetic resonance, and photoluminescence. It has been found that the peculiarities of the formation of nanocrystals, the distribution of nanocrystals over the depth of the implanted layer, the structure, and the character of chemical bonds are similar for both types of oxide matrices; however, the pho toluminescence in the wavelength range 600-1000 nm, which is caused by the nanocrystals in the Al 2 O 3 matrix, has been observed only in the case of the formation of SiO 2 shells around the Si nanocrystals. The surface oxidation of the Si nanocrystals, which is necessary for the formation of SiO 2 shells, is possible due to the presence of excess oxygen in the Al 2 O 3 matrix (the case of Si implantation into the deposited Al 2 O 3 film), as well as due to the inflow of oxygen from the annealing atmosphere (the case of Si implantation into sap phire). In order to verify the quantum confinement mechanism of luminescence, available data on the tem perature dependence of the photoluminescence intensity have been analyzed. An analysis of the mechanisms of charge transfer and electroluminescence excitation in diode structures based on thin ion synthesized layers with silicon nanocrystals has also been performed.