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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 16 — Aug. 1, 2011
  • pp: 15452–15458
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Precipitation of silicon nanoclusters by laser direct-write

Waqas Mustafeez, Daeho Lee, Costas Grigoropoulos, and Alberto Salleo  »View Author Affiliations


Optics Express, Vol. 19, Issue 16, pp. 15452-15458 (2011)
http://dx.doi.org/10.1364/OE.19.015452


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Abstract

The ability to use a laser to direct-write tracks of localized emission enhancement in PECVD-deposited Silicon rich oxide (SRO) films is demonstrated. For this purpose, 400nm thick SRO films with varying excess Si content were irradiated with loosely focused 355nm, 12ps pulses at 80MHz while being translated at 2mm/s. Mapping of areas irradiated with energies between 4.7nJ and 5.5nJ/pulse exhibits regions with the largest emission enhancement. Raman and photoluminescence (PL) measurements suggest precipitation of amorphous and crystalline Si nanoclusters. In the most emissive regions, the PL efficiency of the laser-annealed films was ~70% of that obtained by standard oven-annealing processes. Stress in Si crystals in some areas is identified as leading to quenching of the PL and is hypothesized to be caused by the densification of SRO matrix.

© 2011 OSA

1. Introduction

Crystalline and amorphous nanoclusters in a matrix of SRO have broad emission in 650-900nm range [9

9. H. Rinnert, M. Vergnat, and A. Burneau, “Evidence of light-emitting amorphous silicon clusters confined in a silicon oxide matrix,” J. Appl. Phys. 89(1), 237–243 (2001). [CrossRef]

,10

10. M. Molinari, H. Rinnert, and M. Vergnat, “Effects of the amorphous-crystalline transition on the luminescence of quantum confined silicon nanoclusters,” EPL 66(5), 674–679 (2004) (Europhysics Letters). [CrossRef]

] depending on cluster phase, size distribution, and passivation. The photoluminescence (PL) quantum yield is usually characterized by photoluminescence lifetimes [11

11. R. J. Walters, J. Kalkman, A. Polman, H. A. Atwater, and M. J. A. de Dood, “Photoluminescence quantum efficiency of dense silicon nanocrystal ensembles in SiO_{2},” Phys. Rev. B 73(13), 132302 (2006). [CrossRef]

]. The phase and size information can be obtained from Raman spectroscopy, XRD or TEM. X-ray techniques don't have the necessary spatial resolution for localized analysis, TEM on the other hand only allows the characterization of extremely small volumes raising the issue of the statistical significance of the data. Furthermore, TEM sample preparation is destructive and can release stresses. As a result, TEM characterization may not provide the relevant information to understand the optical properties of Si-NCs as stresses affect the optical properties of the nanocrystals.

SRO films have been used in devices including ring resonators [12

12. R. D. Kekatpure and M. L. Brongersma, “Quantification of free-carrier absorption in silicon nanocrystals with an optical microcavity,” Nano Lett. 8(11), 3787–3793 (2008). [CrossRef] [PubMed]

], photonic crystal cavities [13

13. M. Makarova, J. Vuckovic, H. Sanda, and Y. Nishi, “Silicon-based photonic crystal nanocavity light emitters,” Appl. Phys. Lett. 89(22), 221101 (2006). [CrossRef]

] and even electronically pumped structures [14

14. K. S. Cho, N. Park, T. Kim, K. Kim, G. Y. Sung, and J. H. Shin, “High efficiency visible electroluminescence from silicon nanocrystals embedded in silicon nitride using a transparent doping layer,” Appl. Phys. Lett. 86(7), 071909 (2005). [CrossRef]

]. In all these structures the quantum dots are precipitated throughout the device. However in the case of devices that employ Purcell enhancement through modification of the optical density of states, it might be more suitable to have the gain medium only present inside the cavity to minimize unwanted field interactions. Localized preparation of photonic materials has been explored in many processes from annealing, emissive defects, waveguide writing etc. [15

15. A. H. Nejadmalayeri, P. Scrutton, J. Mak, A. S. Helmy, P. R. Herman, J. Burghoff, S. Nolte, A. Tünnermann, and J. Kaspar, “Solid phase formation of silicon nanocrystals by bulk ultrafast laser-matter interaction,” Opt. Lett. 32(24), 3474–3476 (2007). [CrossRef] [PubMed]

18

18. A. H. Nejadmalayeri and P. R. Herman, “Rapid thermal annealing in high repetition rate ultrafast laser waveguide writing in lithium niobate,” Opt. Express 15(17), 10842–10854 (2007). [CrossRef] [PubMed]

]. and borrows naturally from the strength of laser processing. Here we report on Si nanocluster precipitated in a Si-rich Oxide matrix at high throughput using a high repetition rate ps UV laser. Specifically, we will analyze the spatial distribution of the nanoclusters at two different irradiation energies.

2. Experimental setup

The samples were prepared on quartz and Si substrates via plasma-enhanced chemical vapor deposition (PECVD) at 350°C, 13.56MHz with 40 Watts of RF incident power. The use of different substrates allowed for easier characterization with different techniques. The flow rate ratio (x) of silane (in a 2% SiH4/98% H2 solution) to N2O was varied to control the excess silicon content in the SRO. Approximately 400 nm thick films were obtained with (2%SiH4/98%H2)/(N2O) of x=9.5 (sample A) and x=6 (sample B). X-ray photoelectron spectroscopy (XPS) was used to determine the Si content. For the XPS measurement Ar+ sputtering was performed for subsurface compositional analysis and removing surface impurities. No compositional variation within the specification of the XPS (PHI 5000 Versaprobe) was observed at various depths inside the sample. Spectroscopic ellipsometry was performed to determine the complex refractive index (Table 1

Table 1. SRO compositions and optical properties

table-icon
View This Table
).

Laser processing was performed in ambient with a frequency tripled Nd:YVO4 laser (Newport Vanguard DPSS) with 355nm, 12ps pulses at 80MHz repetition rate. A TEM00, 1mm beam was focused with a single convex lens (f=40mm). The translation speed was kept constant at 2mm/sec while pulse energy was varied from 1.5nJ to 19.4nJ. The estimated spot size was 25μm hence about 1x106 pulses hit each spot. Two tracks separated by 50 µm were prepared at each energy to verify the reproducibility of the process. For comparison, samples annealed in N2 atmosphere at 650, 900 and 1100°C were also prepared. To ensure that Si/SiO2 surface states are passivated and emission is from particulate core rather than defects, the process was completed by performing a forming gas anneal at 450°C for 1 hour on all samples [19

19. S. Cheylan and R. G. Elliman, “Effect of hydrogen on the photoluminescence of Si nanocrystals embedded in a SiO2 matrix,” Appl. Phys. Lett. 78(9), 1225–1227 (2001). [CrossRef]

,20

20. M. López, B. Garrido, C. Garcia, P. Pellegrino, A. Perez-Rodriguez, J. R. Morante, C. Bonafos, M. Carrada, and A. Claverie, “Elucidation of the surface passivation role on the photoluminescence emission yield of silicon nanocrystals embedded in SiO2,” Appl. Phys. Lett. 80(9), 1637–1639 (2002). [CrossRef]

].

3. Results

In order to confirm the presence and investigate the phase of the emitting Si particles, Raman spectra were recorded at different locations across the tracks. Amorphous Si results in a broad peak around 480cm-1 whereas bulk c-Si has a narrow peak at 521cm-1 [24

24. N. Daldosso, G. Das, S. Larcheri, G. Mariotto, G. Dalba, L. Pavesi, A. Irrera, F. Priolo, F. Iacona, and F. Rocca, “Silicon nanocrystal formation in annealed silicon-rich silicon oxide films prepared by plasma enhanced chemical vapor deposition,” J. Appl. Phys. 101(11), 113510 (2007). [CrossRef]

]. The narrow peak at 486cm-1 originates from defects in the quartz substrate, which were present in the control sample as well. Shifts in c-Si peak can be used to determine cluster size and mechanical stresses. A red shift from the bulk value usually corresponds to size reduction due to phonon confinement effects but can also be due to tensile stress. Blue shifts on the other hand can only be caused by compressive stresses. Hence, absolute conclusions cannot be made about the cluster sizes from Raman spectroscopy without knowledge of stresses in the system. In Sample A, track 1, the emerging Raman peak at 480cm-1 obtained in the maximum PL region, leads us to believe that the presence of amorphous nanoclusters (Fig. 3a
Fig. 3 Raman spectra of sample A track 1 and 2 (a) and sample B track 1 (b) showing the evolution of peak position across the track.
) causes the enhanced emission. The PL emission from this region compared well with that from films annealed at 900°C, which is known to be too low a temperature for crystallization in films with similar excess Si content. The edge of track 2 showed some PL emission but most of the central regions were completely quenched. The Raman spectra showed a blue-shifted c-Si right until the edge of the track, where the c-Si peak was red-shifted compared to bulk. The 2cm-1 shift (Fig. 3a) compared to bulk c-Si corresponds to relatively large crystal sizes of 12nm. In contrast an 1100°C annealed sample showed 5cm−1 red shift of the Raman c-Si peak, which corresponds to a crystal size of roughly 4nm.

We also analyzed sample B and observed the Raman spectra across track 1. Figure 3b shows a c-Si peak which is blue shifted by 13cm-1 compared to the bulk Si value. Since the only mechanism for generating a blue shift in Raman spectra is compression, we hypothesize that compression causes rupture of interfacial bonds and introduces non-radiative centers that quench the PL in most of sample B and at the center of track 2, sample A. We can estimate the minimum stress using the analytical expression obtained by Wolf [25

25. I. D. Wolf, “Stress measurements in Si microelectronics devices using Raman spectroscopy,” J. Raman Spectrosc. 30(10), 877–883 (1999). [CrossRef]

]. A 13cm-1 blue shift in the c-Si spectra would suggest 5.6GPa of stress. This peak moves towards the bulk Si value towards the edges suggesting that there is reduction in compressive stress until right at the edge where we see a c-Si shoulder at 517cm-1. Assuming that stress has not changed in nature from compressive to tensile, this shoulder is a clear indication of the presence of Si-NCs. This region coincides with the enhanced PL region in Fig. 1b (cyan marker). It is reasonable to suggest that both a decrease in stress and a reduction in Si-NC size towards the edges of the tracks cause the c-Si Raman peak to red-shift from its initial value at the center of the track (533 cm-1) until its value at the edge (517 cm-1), where emission is observed. The size reduction towards the track edge is further confirmed by the broadening of the Raman peak. The shoulder in figure 3b at 517cm-1 points to an average Si-NC size of 6nm [26

26. G. Faraci, S. Gibilisco, P. Russo, A. R. Pennisi, and S. La Rosa, “Modified Raman confinement model for Si nanocrystals,” Phys. Rev. B 73(3), 033307 (2006). [CrossRef]

]. Given that the PL at this point and along the edge of sample A track 1 are centered at 680nm and 700nm respectively (Fig. 2b), the Si-NC sizes might actually be smaller (~3.5nm) [27

27. G. Ledoux, J. Gong, F. Huisken, O. Guillois, and C. Reynaud, “Photoluminescence of size-separated silicon nanocrystals: Confirmation of quantum confinement,” Appl. Phys. Lett. 80(25), 4834–4836 (2002). [CrossRef]

] and a blue-shift due to residual stress causes us to overestimate the NC size in both cases.

4. Conclusion

Picosecond UV-laser pulses were used to demonstrate high-throughput localized precipitation of Si nanoclusters with a direct-write process. Remarkably, the laser-induced nanocluster precipitation occurs without film cracking. Various pulse energies were used on PECVD-deposited SRO films with two different Si contents. PL emission shows that a suitable regime to obtain good emission after laser irradiation can be obtained. The PL efficiency can be as high as ~70% of that obtained from films processed by conventional oven-anneal methods. Raman data point to phase separation and the presence of amorphous silicon clusters in the primary regions. Higher pulse energies led to crystallization of the clusters but led to densification of the SRO matrix. Due to the nature of the nucleation and growth mechanisms high throughput precipitation requires creating higher temperatures to match the much longer oven anneals, leading to melting and densification. The densification results in compressive stress which leads to the presence of interfacial non-radiative centers, strongly quenching PL in the Si-NCs.

Acknowledgments

WM acknowledges the support from Office of Technology Licensing Stanford Graduate Fellowship. AS gratefully acknowledges support from Electro Scientific Industries. Work done by DL and CPG was supported by NSF under the SINAM NSEC center.

References and Links

1.

D. A. B. Miller, “Optical interconnects to silicon,” Selected. Topics. In Quantum. Electronics. IEEE. Journal. Of. DOI - 10 1109/2944. 902184. 6, 1312–1317 (2000).

2.

L. T. Canham, “Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers,” Appl. Phys. Lett. 57(10), 1046–1048 (1990). [CrossRef]

3.

L. Pavesi, L. Dal Negro, C. Mazzoleni, G. Franzò, and F. Priolo, “Optical gain in silicon nanocrystals,” Nature 408(6811), 440–444 (2000). [CrossRef] [PubMed]

4.

H. Xia, Y. L. He, L. C. Wang, W. Zhang, X. N. Liu, X. K. Zhang, D. Feng, and H. E. Jackson, “Phonon mode study of Si nanocrystals using micro-Raman spectroscopy,” J. Appl. Phys. 78(11), 6705–6708 (1995). [CrossRef]

5.

S. Guha, M. D. Pace, D. N. Dunn, and I. L. Singer, “Visible light emission from Si nanocrystals grown by ion implantation and subsequent annealing,” Appl. Phys. Lett. 70(10), 1207–1209 (1997). [CrossRef]

6.

C. F. Lin, W. T. Tseng, and M. S. Feng, “Formation and characteristics of silicon nanocrystals in plasma-enhanced chemical-vapor-deposited silicon-rich oxide,” J. Appl. Phys. 87(6), 2808–2815 (2000). [CrossRef]

7.

B. Garrido, M. Lopez, O. Gonzalez, A. Perez-Rodriguez, J. R. Morante, and C. Bonafos, “Correlation between structural and optical properties of Si nanocrystals embedded in SiO[sub 2]: The mechanism of visible light emission,” Appl. Phys. Lett. 77(20), 3143–3145 (2000). [CrossRef]

8.

B. Garrido, M. López, A. Pérez-Rodríguez, C. García, P. Pellegrino, R. Ferré, J. A. Moreno, J. R. Morante, C. Bonafos, M. Carrada, A. Claverie, J. de la Torre, and A. Souifi, “Optical and electrical properties of Si-nanocrystals ion beam synthesized in SiO2,” Nucl. Instrum. Methods Phys. Res. B 216, 213–221 (2004). [CrossRef]

9.

H. Rinnert, M. Vergnat, and A. Burneau, “Evidence of light-emitting amorphous silicon clusters confined in a silicon oxide matrix,” J. Appl. Phys. 89(1), 237–243 (2001). [CrossRef]

10.

M. Molinari, H. Rinnert, and M. Vergnat, “Effects of the amorphous-crystalline transition on the luminescence of quantum confined silicon nanoclusters,” EPL 66(5), 674–679 (2004) (Europhysics Letters). [CrossRef]

11.

R. J. Walters, J. Kalkman, A. Polman, H. A. Atwater, and M. J. A. de Dood, “Photoluminescence quantum efficiency of dense silicon nanocrystal ensembles in SiO_{2},” Phys. Rev. B 73(13), 132302 (2006). [CrossRef]

12.

R. D. Kekatpure and M. L. Brongersma, “Quantification of free-carrier absorption in silicon nanocrystals with an optical microcavity,” Nano Lett. 8(11), 3787–3793 (2008). [CrossRef] [PubMed]

13.

M. Makarova, J. Vuckovic, H. Sanda, and Y. Nishi, “Silicon-based photonic crystal nanocavity light emitters,” Appl. Phys. Lett. 89(22), 221101 (2006). [CrossRef]

14.

K. S. Cho, N. Park, T. Kim, K. Kim, G. Y. Sung, and J. H. Shin, “High efficiency visible electroluminescence from silicon nanocrystals embedded in silicon nitride using a transparent doping layer,” Appl. Phys. Lett. 86(7), 071909 (2005). [CrossRef]

15.

A. H. Nejadmalayeri, P. Scrutton, J. Mak, A. S. Helmy, P. R. Herman, J. Burghoff, S. Nolte, A. Tünnermann, and J. Kaspar, “Solid phase formation of silicon nanocrystals by bulk ultrafast laser-matter interaction,” Opt. Lett. 32(24), 3474–3476 (2007). [CrossRef] [PubMed]

16.

L. Khriachtchev, M. Rasanen, and S. Novikov, “Laser-controlled stress of Si nanocrystals in a free-standing Si/SiO[sub 2] superlattice,” Appl. Phys. Lett. 88(1), 013102 (2006). [CrossRef]

17.

C. B. Schaffer, A. Brodeur, J. F. García, and E. Mazur, “Micromachining bulk glass by use of femtosecond laser pulses with nanojoule energy,” Opt. Lett. 26(2), 93–95 (2001). [CrossRef] [PubMed]

18.

A. H. Nejadmalayeri and P. R. Herman, “Rapid thermal annealing in high repetition rate ultrafast laser waveguide writing in lithium niobate,” Opt. Express 15(17), 10842–10854 (2007). [CrossRef] [PubMed]

19.

S. Cheylan and R. G. Elliman, “Effect of hydrogen on the photoluminescence of Si nanocrystals embedded in a SiO2 matrix,” Appl. Phys. Lett. 78(9), 1225–1227 (2001). [CrossRef]

20.

M. López, B. Garrido, C. Garcia, P. Pellegrino, A. Perez-Rodriguez, J. R. Morante, C. Bonafos, M. Carrada, and A. Claverie, “Elucidation of the surface passivation role on the photoluminescence emission yield of silicon nanocrystals embedded in SiO2,” Appl. Phys. Lett. 80(9), 1637–1639 (2002). [CrossRef]

21.

L. Vaccaro, M. Cannas, and R. Boscaino, “Phonon coupling of non-bridging oxygen hole center with the silica environment: Temperature dependence of the 1.9 eV emission spectra,” J. Lumin. 128(7), 1132–1136 (2008). [CrossRef]

22.

A. Morales, J. Barreto, C. Domínguez, M. Riera, M. Aceves, and J. Carrillo, “Comparative study between silicon-rich oxide films obtained by LPCVD and PECVD,” Physica E 38(1-2), 54–58 (2007). [CrossRef]

23.

F. Iacona, C. Bongiorno, C. Spinella, S. Boninelli, and F. Priolo, “Formation and evolution of luminescent Si nanoclusters produced by thermal annealing of SiOx films,” J. Appl. Phys. 95(7), 3723–3732 (2004). [CrossRef]

24.

N. Daldosso, G. Das, S. Larcheri, G. Mariotto, G. Dalba, L. Pavesi, A. Irrera, F. Priolo, F. Iacona, and F. Rocca, “Silicon nanocrystal formation in annealed silicon-rich silicon oxide films prepared by plasma enhanced chemical vapor deposition,” J. Appl. Phys. 101(11), 113510 (2007). [CrossRef]

25.

I. D. Wolf, “Stress measurements in Si microelectronics devices using Raman spectroscopy,” J. Raman Spectrosc. 30(10), 877–883 (1999). [CrossRef]

26.

G. Faraci, S. Gibilisco, P. Russo, A. R. Pennisi, and S. La Rosa, “Modified Raman confinement model for Si nanocrystals,” Phys. Rev. B 73(3), 033307 (2006). [CrossRef]

27.

G. Ledoux, J. Gong, F. Huisken, O. Guillois, and C. Reynaud, “Photoluminescence of size-separated silicon nanocrystals: Confirmation of quantum confinement,” Appl. Phys. Lett. 80(25), 4834–4836 (2002). [CrossRef]

28.

F. Vega, J. Armengol, V. Diez-Blanco, J. Siegel, J. Solis, B. Barcones, A. Perez-Rodriguez, and P. Loza-Alvarez, “Mechanisms of refractive index modification during femtosecond laser writing of waveguides in alkaline lead-oxide silicate glass,” Appl. Phys. Lett. 87(2), 021109 (2005). [CrossRef]

29.

L. Huang and J. Kieffer, “Anomalous thermomechanical properties and laser-induced densification of vitreous silica,” Appl. Phys. Lett. 89(14), 141915 (2006). [CrossRef]

OCIS Codes
(140.3390) Lasers and laser optics : Laser materials processing

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: March 24, 2011
Revised Manuscript: June 3, 2011
Manuscript Accepted: June 6, 2011
Published: July 28, 2011

Citation
Waqas Mustafeez, Daeho Lee, Costas Grigoropoulos, and Alberto Salleo, "Precipitation of silicon nanoclusters by laser direct-write," Opt. Express 19, 15452-15458 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-16-15452


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References

  1. D. A. B. Miller, “Optical interconnects to silicon,” Selected. Topics. In Quantum. Electronics. IEEE. Journal. Of. DOI - 10 1109/2944. 902184. 6, 1312–1317 (2000).
  2. L. T. Canham, “Silicon quantum wire array fabrication by electrochemical and chemical dissolution of wafers,” Appl. Phys. Lett. 57(10), 1046–1048 (1990). [CrossRef]
  3. L. Pavesi, L. Dal Negro, C. Mazzoleni, G. Franzò, and F. Priolo, “Optical gain in silicon nanocrystals,” Nature 408(6811), 440–444 (2000). [CrossRef] [PubMed]
  4. H. Xia, Y. L. He, L. C. Wang, W. Zhang, X. N. Liu, X. K. Zhang, D. Feng, and H. E. Jackson, “Phonon mode study of Si nanocrystals using micro-Raman spectroscopy,” J. Appl. Phys. 78(11), 6705–6708 (1995). [CrossRef]
  5. S. Guha, M. D. Pace, D. N. Dunn, and I. L. Singer, “Visible light emission from Si nanocrystals grown by ion implantation and subsequent annealing,” Appl. Phys. Lett. 70(10), 1207–1209 (1997). [CrossRef]
  6. C. F. Lin, W. T. Tseng, and M. S. Feng, “Formation and characteristics of silicon nanocrystals in plasma-enhanced chemical-vapor-deposited silicon-rich oxide,” J. Appl. Phys. 87(6), 2808–2815 (2000). [CrossRef]
  7. B. Garrido, M. Lopez, O. Gonzalez, A. Perez-Rodriguez, J. R. Morante, and C. Bonafos, “Correlation between structural and optical properties of Si nanocrystals embedded in SiO[sub 2]: The mechanism of visible light emission,” Appl. Phys. Lett. 77(20), 3143–3145 (2000). [CrossRef]
  8. B. Garrido, M. López, A. Pérez-Rodríguez, C. García, P. Pellegrino, R. Ferré, J. A. Moreno, J. R. Morante, C. Bonafos, M. Carrada, A. Claverie, J. de la Torre, and A. Souifi, “Optical and electrical properties of Si-nanocrystals ion beam synthesized in SiO2,” Nucl. Instrum. Methods Phys. Res. B 216, 213–221 (2004). [CrossRef]
  9. H. Rinnert, M. Vergnat, and A. Burneau, “Evidence of light-emitting amorphous silicon clusters confined in a silicon oxide matrix,” J. Appl. Phys. 89(1), 237–243 (2001). [CrossRef]
  10. M. Molinari, H. Rinnert, and M. Vergnat, “Effects of the amorphous-crystalline transition on the luminescence of quantum confined silicon nanoclusters,” EPL 66(5), 674–679 (2004) (Europhysics Letters). [CrossRef]
  11. R. J. Walters, J. Kalkman, A. Polman, H. A. Atwater, and M. J. A. de Dood, “Photoluminescence quantum efficiency of dense silicon nanocrystal ensembles in SiO_{2},” Phys. Rev. B 73(13), 132302 (2006). [CrossRef]
  12. R. D. Kekatpure and M. L. Brongersma, “Quantification of free-carrier absorption in silicon nanocrystals with an optical microcavity,” Nano Lett. 8(11), 3787–3793 (2008). [CrossRef] [PubMed]
  13. M. Makarova, J. Vuckovic, H. Sanda, and Y. Nishi, “Silicon-based photonic crystal nanocavity light emitters,” Appl. Phys. Lett. 89(22), 221101 (2006). [CrossRef]
  14. K. S. Cho, N. Park, T. Kim, K. Kim, G. Y. Sung, and J. H. Shin, “High efficiency visible electroluminescence from silicon nanocrystals embedded in silicon nitride using a transparent doping layer,” Appl. Phys. Lett. 86(7), 071909 (2005). [CrossRef]
  15. A. H. Nejadmalayeri, P. Scrutton, J. Mak, A. S. Helmy, P. R. Herman, J. Burghoff, S. Nolte, A. Tünnermann, and J. Kaspar, “Solid phase formation of silicon nanocrystals by bulk ultrafast laser-matter interaction,” Opt. Lett. 32(24), 3474–3476 (2007). [CrossRef] [PubMed]
  16. L. Khriachtchev, M. Rasanen, and S. Novikov, “Laser-controlled stress of Si nanocrystals in a free-standing Si/SiO[sub 2] superlattice,” Appl. Phys. Lett. 88(1), 013102 (2006). [CrossRef]
  17. C. B. Schaffer, A. Brodeur, J. F. García, and E. Mazur, “Micromachining bulk glass by use of femtosecond laser pulses with nanojoule energy,” Opt. Lett. 26(2), 93–95 (2001). [CrossRef] [PubMed]
  18. A. H. Nejadmalayeri and P. R. Herman, “Rapid thermal annealing in high repetition rate ultrafast laser waveguide writing in lithium niobate,” Opt. Express 15(17), 10842–10854 (2007). [CrossRef] [PubMed]
  19. S. Cheylan and R. G. Elliman, “Effect of hydrogen on the photoluminescence of Si nanocrystals embedded in a SiO2 matrix,” Appl. Phys. Lett. 78(9), 1225–1227 (2001). [CrossRef]
  20. M. López, B. Garrido, C. Garcia, P. Pellegrino, A. Perez-Rodriguez, J. R. Morante, C. Bonafos, M. Carrada, and A. Claverie, “Elucidation of the surface passivation role on the photoluminescence emission yield of silicon nanocrystals embedded in SiO2,” Appl. Phys. Lett. 80(9), 1637–1639 (2002). [CrossRef]
  21. L. Vaccaro, M. Cannas, and R. Boscaino, “Phonon coupling of non-bridging oxygen hole center with the silica environment: Temperature dependence of the 1.9 eV emission spectra,” J. Lumin. 128(7), 1132–1136 (2008). [CrossRef]
  22. A. Morales, J. Barreto, C. Domínguez, M. Riera, M. Aceves, and J. Carrillo, “Comparative study between silicon-rich oxide films obtained by LPCVD and PECVD,” Physica E 38(1-2), 54–58 (2007). [CrossRef]
  23. F. Iacona, C. Bongiorno, C. Spinella, S. Boninelli, and F. Priolo, “Formation and evolution of luminescent Si nanoclusters produced by thermal annealing of SiOx films,” J. Appl. Phys. 95(7), 3723–3732 (2004). [CrossRef]
  24. N. Daldosso, G. Das, S. Larcheri, G. Mariotto, G. Dalba, L. Pavesi, A. Irrera, F. Priolo, F. Iacona, and F. Rocca, “Silicon nanocrystal formation in annealed silicon-rich silicon oxide films prepared by plasma enhanced chemical vapor deposition,” J. Appl. Phys. 101(11), 113510 (2007). [CrossRef]
  25. I. D. Wolf, “Stress measurements in Si microelectronics devices using Raman spectroscopy,” J. Raman Spectrosc. 30(10), 877–883 (1999). [CrossRef]
  26. G. Faraci, S. Gibilisco, P. Russo, A. R. Pennisi, and S. La Rosa, “Modified Raman confinement model for Si nanocrystals,” Phys. Rev. B 73(3), 033307 (2006). [CrossRef]
  27. G. Ledoux, J. Gong, F. Huisken, O. Guillois, and C. Reynaud, “Photoluminescence of size-separated silicon nanocrystals: Confirmation of quantum confinement,” Appl. Phys. Lett. 80(25), 4834–4836 (2002). [CrossRef]
  28. F. Vega, J. Armengol, V. Diez-Blanco, J. Siegel, J. Solis, B. Barcones, A. Perez-Rodriguez, and P. Loza-Alvarez, “Mechanisms of refractive index modification during femtosecond laser writing of waveguides in alkaline lead-oxide silicate glass,” Appl. Phys. Lett. 87(2), 021109 (2005). [CrossRef]
  29. L. Huang and J. Kieffer, “Anomalous thermomechanical properties and laser-induced densification of vitreous silica,” Appl. Phys. Lett. 89(14), 141915 (2006). [CrossRef]

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