Correlation between structural and optical properties of Si nanocrystals embedded in SiO2: The mechanism of visible light emission

Garrido, B.; López, M.; González, Óscar Clavería; Pérez-Rodrı́guez, A.; Morante, J.R.; Bonafos, Caroline

doi:10.1063/1.1325392

Cited by 93 publications

(65 citation statements)

References 17 publications

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“…A strong emission band peaked around 1.45 6 0.05 eV was found, in agreement with data reported in the literature. 7,8,19 As noticed by Garrido et al, 7 the emission energy is affected by a Stokes shift of 0.26 6 0.03 eV with respect to the absorption energy irrespective of the size of the Si ncs. Taking in account this effect, the optical band gap of the Si ncs embedded in SiO 2 matrix was evaluated to be 1.7 6 0.1 eV.…”

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confidence: 67%

“…Several theoretical works described this issue 5 and different optical techniques as photoluminescence (PL), spectroscopic ellissometry, and optical absorption have been used to prove this fact. [6][7][8] On the other hand, in the perspective of the technological applications, a lot of works has been carried out on the electrical characteristics, in particular related to the charge trapping properties of the Si ncs based metal-oxide-semiconductor (MOS) structures. 9 Among these wide characterization efforts, the direct measurement of the Si ncs energy alignment in the SiO 2 host is still lacking.…”

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confidence: 99%

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The energy band alignment of Si nanocrystals in SiO2

Seguini

Schamm-Chardon²,

Pellegrino³

et al. 2011

Applied Physics Letters

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The determination of the energy band alignment between the 2.6-nm-diameter Si nanocrystals and the SiO2 host is achieved by means of photo-ionization/-neutralization and capacitance spectroscopy. The measured conduction and valence band offsets are 2.6 eV and 4.4 eV. The band gap is evaluated to be 1.7 eV by photoluminescence. These results indicate that the valence band offset at the Si nanocrystals/SiO2 interface is quite close to the one observed at bulk Si/SiO2 interface. On the contrary, we observe a clear upward shift (0.5 eV) of the conduction band in the Si nanocrystals/SiO2 system with respect to the bulk Si/SiO2 hetero-structure.

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confidence: 67%

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confidence: 99%

The energy band alignment of Si nanocrystals in SiO2

Seguini

Schamm-Chardon²,

Pellegrino³

et al. 2011

Applied Physics Letters

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“…[11][12][13][14] Besides the QC effect for explaining the new optical properties of nanometer-scaled Si films, some studies also pointed out the important role played by the Si/ SiO 2 interface in the PL. 13,[15][16][17] Thus, the PL of Si nanocluster ͑Si-ncl͒ is governed by key parameters such as grain size and the Si/ SiO 2 phase separation. An efficient absorption of light by the solar cell can be reached through the optimization of the density of Si-ncl, the Si-ncl size for a control of the absorbed wavelength of the solar spectrum, and the Si/ SiO 2 interface quality.…”

Section: Introductionmentioning

confidence: 99%

Silicon-rich SiO2/SiO2 multilayers: A promising material for the third generation of solar cell

Gourbilleau

Ternon

Maestre

et al. 2009

Journal of Applied Physics

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Method for fabricating third generation photovoltaic cells based on Si quantum dots using ion implantation into SiO2 J. Appl. Phys. 109, 084337 (2011) Si-rich-SiO 2 ͑SRSO͒ / SiO 2 multilayers ͑MLs͒ have been grown by reactive magnetron sputtering. The presence of silicon nanoclusters ͑Si-ncls͒ within the SRSO sublayer and annealing temperature influence optical absorption as well as photoluminescence. The optimized annealing temperature has been found to be 1100°C, which allows the recovery of defects and thus enhances photoluminescence. Four MLs with Si-ncl size ranging from 1.5 to 8 nm have been annealed using the optimized conditions and then studied by transmission measurements. Optical absorption has been modeled so that a size effect in the linear absorption coefficient ␣ ͑in cm −1 ͒ has been evidenced and correlated with TEM observations. It is demonstrated that amorphous Si-ncl absorption is fourfold higher than that of crystalline Si-ncls.

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“…We have recently proposed the assistance of Si-O vibrations at the interface as the possible dominant path for the recombination of electron-hole pairs in Si nanocrystals embedded in SiO 2 . 16 The interfaces are so important that its passivation against nonradiative states and defects is necessary to increase the radiative yield of the emission of Si nanocrystals, with independence of the emission mechanism. There are some reports on the increase of radiative efficiency by performing H passivation through standard forming gas annealing.…”

Section: Introductionmentioning

confidence: 99%

“…This emission has been unambiguously linked to the presence of Si nanocrystals in an oxide matrix. 3,8,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] Nevertheless, the mechanism of the dominant radiative recombination mechanism is still under debate, as in porous silicon.…”

Section: Introductionmentioning

confidence: 99%

Influence of average size and interface passivation on the spectral emission of Si nanocrystals embedded in SiO2

Fernández

López

Garcı́a

et al. 2002

Journal of Applied Physics

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260

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The correlation between the structural ͑average size and density͒ and optoelectronic properties ͓band gap and photoluminescence ͑PL͔͒ of Si nanocrystals embedded in SiO 2 is among the essential factors in understanding their emission mechanism. This correlation has been difficult to establish in the past due to the lack of reliable methods for measuring the size distribution of nanocrystals from electron microscopy, mainly because of the insufficient contrast between Si and SiO 2 . With this aim, we have recently developed a successful method for imaging Si nanocrystals in SiO 2 matrices. This is done by using high-resolution electron microscopy in conjunction with conventional electron microscopy in dark field conditions. Then, by varying the time of annealing in a large time scale we have been able to track the nucleation, pure growth, and ripening stages of the nanocrystal population. The nucleation and pure growth stages are almost completed after a few minutes of annealing time at 1100°C in N 2 and afterward the ensemble undergoes an asymptotic ripening process. In contrast, the PL intensity steadily increases and reaches saturation after 3-4 h of annealing at 1100°C. Forming gas postannealing considerably enhances the PL intensity but only for samples annealed previously in less time than that needed for PL saturation. The effects of forming gas are reversible and do not modify the spectral shape of the PL emission. The PL intensity shows at all times an inverse correlation with the amount of P b paramagnetic centers at the Si-SiO 2 nanocrystal-matrix interfaces, which have been measured by electron spin resonance. Consequently, the P b centers or other centers associated with them are interfacial nonradiative channels for recombination and the emission yield largely depends on the interface passivation. We have correlated as well the average size of the nanocrystals with their optical band gap and PL emission energy. The band gap and emission energy shift to the blue as the nanocrystal size shrinks, in agreement with models based on quantum confinement. As a main result, we have found that the Stokes shift is independent of the average size of nanocrystals and has a constant value of 0.26Ϯ0.03 eV, which is almost twice the energy of the Si-O vibration. This finding suggests that among the possible channels for radiative recombination, the dominant one for Si nanocrystals embedded in SiO 2 is a fundamental transition spatially located at the Si-SiO 2 interface with the assistance of a local Si-O vibration.

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Correlation between structural and optical properties of Si nanocrystals embedded in SiO2: The mechanism of visible light emission

Cited by 93 publications

References 17 publications

The energy band alignment of Si nanocrystals in SiO2

The energy band alignment of Si nanocrystals in SiO2

Silicon-rich SiO2/SiO2 multilayers: A promising material for the third generation of solar cell

Influence of average size and interface passivation on the spectral emission of Si nanocrystals embedded in SiO2

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