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Optics Express

Optics Express

  • Editor: Andrew M. Weiner
  • Vol. 21, Iss. 13 — Jul. 1, 2013
  • pp: 15888–15895
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Enhanced white photoluminescence in silicon-rich oxide/SiO2 superlattices by low-energy ion-beam treatment

Chuan-Feng Shih, Chu-Yun Hsiao, and Kuan-Wei Su  »View Author Affiliations


Optics Express, Vol. 21, Issue 13, pp. 15888-15895 (2013)
http://dx.doi.org/10.1364/OE.21.015888


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Abstract

This study presents the crystalline and luminescence properties of silicon-rich oxide (SRO)/SiO2 superlattices in which the SRO layers were prepared with a low-energy (<60 eV) argon ion-beam treatment. Experimental results evidenced that density of the Si nanocrystals (NCs) in the SRO layer was increased by ion-beam treatment after annealing, increasing the surface roughness. The stoichiometry of the as-prepared SRO layer was unchanged but the phase separation of the annealed SRO layer was enhanced by the ion-beam treatment, yielding visible white photoluminescence from the E’ centers and Si NCs.

© 2013 OSA

1. Introduction

Silicon-rich oxide (SRO) or nitride (SRN) films in which are embedded silicon nanocrystals (Si NCs) have been demonstrated to exhibit visible luminescence and to be integratable with Si technology, with great potential as next-generation solid-state lighting sources with large area scalability and low production cost [1

1. C. K. Tseng, M. C. M. Lee, H. W. Hung, J. R. Huang, K. Y. Lee, J. M. Shieh, and G. R. Lin, “Silicon-nanocrystal resonant-cavity light emitting devices for color tailoring,” J. Appl. Phys. 111(7), 074512 (2012). [CrossRef]

]. Light-emitting diodes (LEDs) that are based on SRN films have a low operating voltage and can cover all visible wavelengths, owing to their low potential barrier and the low density of interfacial states between the SRN and Si NCs [2

2. G. R. Lin, Y. H. Pai, C. T. Lin, and C. C. Chen, “Comparison on the electroluminescence of Si-rich SiNx and SiOx based light-emitting diodes,” Appl. Phys. Lett. 96(26), 263514 (2010). [CrossRef]

,3

3. D. Di, I. Perez-Wurfl, L. Wu, Y. Huang, A. Marconi, A. Tengattini, A. Anopchenko, L. Pavesi, and G. Conibeer, “Electroluminescence from Si nanocrystal/c-Si heterojunction light-emitting diodes,” Appl. Phys. Lett. 99(25), 251113 (2011). [CrossRef]

]. White-light LEDs have been obtained by stacking several SRN or SRN/SRO layers with differently sized Si-NCs [4

4. Y. Berencén, J. Carreras, O. Jambois, J. M. Ramírez, J. A. Rodríguez, C. Domínguez, C. E. Hunt, and B. Garrido, “Metal-nitride-oxide-semiconductor light-emitting devices for general lighting,” Opt. Express 19(S3Suppl 3), A234–A244 (2011). [CrossRef] [PubMed]

]. However, the quantum efficiency of such SRN-based LEDs is low, owing to insufficient quantum confinement and low carrier retention [5

5. N. M. Park, T. S. Kim, and S. J. Park, “Band gap engineering of amorphous silicon quantum dots for light-emitting diodes,” Appl. Phys. Lett. 78(17), 2575–2577 (2001). [CrossRef]

]. Therefore, recent research into Si NCs focused on SRO-based devices for lighting purposes.

Although the free-standing Si NCs that were made by electrochemical methods showed high quantum efficiency and tunable band gap [6

6. C. C. Tu, Q. Zhang, L. Y. Lin, and G. Cao, “Brightly photoluminescent phosphor materials based on silicon quantum dots with oxide shell passivation,” Opt. Express 20(S1), A69–A74 (2012). [CrossRef] [PubMed]

], they are difficult to integrate with the thin-film technologies. The application of them was focused on passive light-converting materials. As for the case of thin films, SRO films with embedded Si NCs have been fabricated by the oxidation of Si nanostructures, the annealing of Si-ion-implanted SiO2, and the annealing of vacuum-deposited SRO films [7

7. M. C. Kim, S. Kim, S. H. Choi, and S. Park, “Anomalous light-induced enhancement of photoluminescence from Si nanocrystals fabricated by thermal oxidation of amorphous Si,” Appl. Phys. Lett. 91(3), 033111 (2007). [CrossRef]

9

9. M. Kulakci, U. Serincan, and R. Turan, “Electroluminescence generated by a metal oxide semiconductor light emitting diode (MOS-LED) with Si nanocrystals embedded in SiO2 layers by ion implantation,” Semicond. Sci. Technol. 21(12), 1527–1532 (2006). [CrossRef]

]. Implanting Si ions into SiO2 generates separate blue-green and red-orange photoluminescence (PL) bands, whose intensity depends on the amount of excess Si and the annealing time. White PL has been observed by co-implanting high doses Si or C ions into SiO2 and post-annealing [10

10. Y. Ou, V. Jokubavicius, S. Kamiyama, C. Liu, R. W. Berg, M. Linnarsson, R. Yakimova, M. Syväjärvi, and H. Ou, “Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC,” Opt. Mater. Express 1(8), 1439–1446 (2011). [CrossRef]

]. Emission from both oxygen-related defects (blue-green) and quantum-confined Si NCs (red-infrared) suggests a way to achieve white-light emission. However, implantation induces many defects and the corresponding spectra typically include up to three bands. The high color rendering reduces luminous efficiency. SRO films that are fabricated by common thin-film deposition technique like plasma-enhanced chemical vapor deposition generally exhibit sharp red-orange luminescence. However, the blue-green luminescence of such films is weak because of a lack of radiative recombination centers and the inhibition of size-dependent band-gap widening by highly localized interfacial states [11

11. R. Huang, K. Chen, H. Dong, D. Wang, H. Ding, W. Li, J. Xu, Z. Ma, and L. Xu, “Enhanced electroluminescence efficiency of oxidized amorphous silicon nitride light-emitting devices by modulating Si/N ratio,” Appl. Phys. Lett. 91(11), 111104 (2007). [CrossRef]

]. Earlier, sputtering has been used to synthesis the SRO films. Broad spectrum was obtained. Besides, ion-beam assisted deposition has been attempted to synthesize the SRO films. Unfortunately, the phase separation of the SRO films was reduced because of the preferring bombardment of Si [12

12. J. K. Kim, K. M. Cha, J. H. Kang, Y. Kim, J. Y. Yi, T. H. Chung, and H. J. Bark, “Area-selective formation of Si nanocrystals by assisted ion-beam irradiation during dual-ion-beam deposition,” Appl. Phys. Lett. 85(9), 1595 (2004). [CrossRef]

].

2. Experiment

Figure 1
Fig. 1 Illustration of two-gun sputtering system equipped with an ion source and an plasma-bridge neutralizer. By rotating substrate, 20-periods SRO/SiO2 superlattices were deposited alternatively. SRO layer was treated by low-energy Ar ion-beam just after deposition.
illustrates the simplified deposition system. An end-hole gridless ion source with a plasma bridge neutralizer and two sputtering guns were used to prepare SRO/SiO2 supperlattices. The anode voltage of the Ar ion source was varied from 0 to 60 V, yielding an ion energy of 0-60 eV. Metal plates were used to shield the interaction between the ion beam and other plasma sources (Si, SiO2). The Ar ion-beam irradiated on the SRO layer as the substrate rotated. The ion beam affected mainly the surface reactions of the SRO films rather than the plasma chemistry. Twenty-period SRO/SiO2 superlattices were deposited on p-type (100) Si wafer by repeating the following procedure: a 2 nm-thick SiO2 layer was firstly deposited by the rf-sputtering of an SiO2 target; then a 4 nm-thick SRO layer was deposited by the dc-sputtering of a pure Si target, and the Ar ion-beam was then irradiated on the SRO surface by rotating the substrate. The Ar (20 sccm) gas was introduced into the chamber during deposition. Post-annealing was performed at 1000 °C for 180 min in a furnace with flowing forming gas (95%N2 + 5% H2). X-ray photoelectron spectroscopy (XPS), cross-sectional high-resolution transmission-electron microscopy (HR-TEM, JEOL/JEM-2100) and grazing-angle X-ray diffraction (GIXRD, Siemens/D5000) were used to investigate the films. Atomic-force microscopy was used to observe the surface morphology. An He-Cd laser (325 nm) with a power of ~40 mW was used for PL measurement.

3. Results and discussion

Control of the phase separation of thin-film SiOx (x<2) into nanocrystalline Si and SiO2 is known to strongly depend on thermal annealing [13

13. H. L. Hao, L. K. Wu, and W. Z. Shen, “Controlling the red luminescence from silicon quantum dots in hydrogenated amorphous silicon nitride films,” Appl. Phys. Lett. 92(12), 121922 (2008). [CrossRef]

]. Figure 2
Fig. 2 (a) (b) Bright-field and (c)(d) dark-field HR-TEM cross-section images of SRO/SiO2 films. (a) (c) 0 V ion energy, and (b)(d) 40 V anode voltages. Insets show diffraction patterns. The ion-beam incident only on the SRO layers.
displays the HR-TEM images of the annealed SRO films. The bright-field images [Figs. 2(a) and 2(b)] demonstrate that interface of the SRO/SiO2 superlattices was abrupt and all SRO layers had the same thickness. It indicated that the sputtering and densification effects of the ion-beam on the growing films could be ignored. Figures 2(c) and 2(d) show the dark field HRTEM images. Amount of white spots was increased by the ion-beam treatment, revealing an increase in the density of Si NCs (white spots) in the SRO film.

TEM images usually present very local information in nano-meter scale. Therefore, XRD was performed to further determine the crystalline behaviors of Si NCs. Figure 3
Fig. 3 X-ray diffraction patterns of annealed SRO/SiO2 films prepared by various anode voltages.
presents the GIXRD patterns of the SRO/SiO2 multilayers in which the SRO layers were treated using various ion energies. Ion-beam treatment of the SRO layer markedly increased the XRD intensity, indicating an increase in Si content. Moreover, the full-width at half maximum of XRD peaks increased with ion-beam energy, showing a decrease in grain size according to Sherrer’s law. Figure 4(a)
Fig. 4 Atomic force microscopic images of SRO/SiO2 films in which SRO layers were treated by (a)(c) 0 V and (b)(d) 40 V ion-beams. (a)(b) and (c)(d) were as-prepared and annealed samples.
-4(d) show the AFM images. It was found that the ion-beam did not change the surface roughness of the as-prepared sample, but it did increase that of the annealed samples, and this effect was evidently associated with the formation of Si NCs [14

14. M. Fukuda, K. Nakagawa, S. Miyazaki, and M. Hirose, “Resonant tunneling through a self-assembled Si quantum dot,” Appl. Phys. Lett. 70(17), 2291–2293 (1997). [CrossRef]

]. Accordingly, the nanostructural observations implied that the ion-beam enhanced the phase separation of SRO films after annealing.

Figure 5
Fig. 5 XPS spectra of Si 2p of SRO layers before (left) and after annealing (right) treated by different ion energies. XPS signals were taken from depth-profile analysis of SRO/SiO2 superlattices.
displays the Si 2p XPS spectra of the annealed and as-prepared SRO layers that were treated using various ion energies. Quantitative analysis revealed that the stoichiometry of the as-prepared SRO films(x in SiOx) was unchanged by the ion-beam because the sputtering yields (Y(E)) of the oxygen and silicon atoms from the Ar ion sources were similar, according to the equation:
Y(E)=0.042UbαSn(E)
(1)
where E is the energy of the initially incident particle; Ub is the surface binding energy; α is associated with the mass of the incident particle and the target particle, and Sn(E) is the energy-dependent nuclear stopping cross-section [15

15. P. Sigmund, “Theory of Sputtering. I. Sputtering Yield of Amorphous and Polycrystalline Targets,” Phys. Rev. 184(2), 383–416 (1969). [CrossRef]

]. The spectra of annealed SRO films that were treated by ion-beam yielded a shoulder emerged in the high binding energy side (~104 eV). The appearance of the high binding energy feature was associated with the increases in both the Si0+ and Si4+ contents, which were determined by fitting the XPS profiles by five Gaussian functions (Si0+, Si1+, Si2+, Si3+, Si4+) (Table 1

Table 1. Characteristics of ion-beam-assisted SRO films (XPS) and SRO/SiO2 superlattices (roughness and XRD intensity).

table-icon
View This Table
). The phase separation of SRO layer was greatly enhanced by the low-energy ion-beam treatment. This finding contradicted the studies of Kim [12

12. J. K. Kim, K. M. Cha, J. H. Kang, Y. Kim, J. Y. Yi, T. H. Chung, and H. J. Bark, “Area-selective formation of Si nanocrystals by assisted ion-beam irradiation during dual-ion-beam deposition,” Appl. Phys. Lett. 85(9), 1595 (2004). [CrossRef]

], in which the ion-beam caused a preferential sputtering of Si, which inhibited the phase separation. Similarly, Lee used ion-beam with 200-600 eV to assist depositing SiOx films [16

16. W. Ensinger, “Low energy ion assist during deposition - an effective tool for controlling thin film microstructure,” Nucl. Instrum. Methods Phys. Res. 127–128, 796–808 (1997).

]. Only improvements in the optical properties and film density were obtained. It was believed that the re-sputtering effect occurred when a higher ion-beam energy was used (>1000 eV) [17

17. C. C. Lee and S. L. Ku, “Optical and structural properties of SiOx films from ion-assisted deposition,” Thin Solid Films 518(17), 4804–4808 (2010). [CrossRef]

]. Therefore, the ion energy was responsible for the different observations of how the ion beam influenced the SRO films. From a thermodynamic perspective, the formation of the Si NCs within the SRO films was a result of a demixing process of Si and O atoms. Because the bonding energy of Si-Si was smaller than that of Si-O or Si = O [18

18. S. S. Zumdahl, Chemistry, 4th ed. (Houghton Mifflin, 1997), chap. 8.

], the ion-beam possibly broke the Si-Si bonds that reduced the size of the Si clusters or introduced dangling bonds, increasing the total free energy that drove the decomposition of the SRO layer. Based on the XPS results, models of atomic arrangement of Si NCs were represented in Figs. 6(a)
Fig. 6 Atomic models of Si NCs prepared by (a) sputtering (b) sputtering with ion-beam treatment.
and 6(b). The Si NCs that were prepared by ion-beam treatment were surrounded by SiO2; while that deposited by sputtering were surrounded by Si1+, Si2+, and Si 3+ atoms.

Figure 7(a)
Fig. 7 (a) PL spectra of SRO/SiO2 superlattices prepared by 0V (square) and 40V (triangle) anode voltages of ion-beams. Inset shows curve fitting results of SRO/SiO2 film prepared by 40 V ion-beam treated SRO. The white-light PL of SRO/SiO2 superlattices exited by He-Cd laser was also shown. (b) CIE chromaticity diagram of SRO/SiO2 superlattices deposited with 0 V and 40 V ion-beam treatment.
shows the PL spectra. The PL peak in the vicinity of ~750 nm was slightly blue-shifted by ion-beam treatment, also suggesting a reduction of the Si cluster size by the ion-beam. Additionally, this peak was further blue-shifted when the sample was annealed in an oxygen ambient, confirming that this emission was associated with the radiative recombination of Si NCs. The PL spectrum of the as-prepared SRO film that was treated using ion-beam was resolved by three Gaussian functions that were centered at 410, 450, and 510 nm, representing the weak oxygen bond (WOB), the neutral oxygen vacancy (NOV), and the E’ center, respectively [19

19. G. R. Lin, C. J. Lin, C. K. Lin, L. J. Chou, and Y. L. Chueh, “Oxygen defect and Si nanocrystal dependent white-light and near-infrared electroluminescence of Si-implanted and plasma-enhanced chemical-vapor deposition-grown Si-rich SiO2,” J. Appl. Phys. 97(9), 094306 (2005). [CrossRef]

]. The diamagnetic NOV center at 2.7 eV (~450 nm) dominated the luminescence of the SRO film that was not treated by ion-beam and annealing. On the contrary, strong luminescence from E’ centers dominated the PL of the ion-beam-treated SRO sample. In both cases, after annealing most of the NOV defects had been transferred to the E’ centers. This phenomenon was associated with hole trapping [20

20. H. Nishikawa, E. Watanabe, D. Ito, M. Takiyama, A. Ieki, and Y. Ohki, “Photoluminescence study of defects in ion-implanted thermal SiO2 films,” J. Appl. Phys. 78(2), 842–846 (1995). [CrossRef]

]. The presence of the E’ centers that were enhanced by ion-beam treatment was further confirmed by the electron paramagnetic resonance (EPR) signals around 3498 Gauss (Fig. 8
Fig. 8 Electron paramagnetic resonance signals of SRO films that were prepared with ion-beam treatment and annealing.
). Very weak EPR signal was obtained for SRO film that was simply prepared by sputtering. Figure 7(b) points the position of the spectra in the CIE chromaticity diagram. The ion-beam treatment increased the color temperature of the SRO from 3021 to 5204 K. Additionally, visible electroluminescence with little Stark shift was obtained, and the PL quantum yield was roughly around 2%, suggesting that the low-energy ion-beam-assisted sputtering process has the potential to make Si-based lighting devices. Table 1 summarizes the changes in binding energies and roughness of the SRO films to which were applied annealing and ion-beams.

4. Conclusion

In summary, a low-energy ion-beam was used to assist the sputtering of SRO films. The density of Si NCs in SRO films was thus increased, increasing their surface roughness. Quantitative analysis showed that the ion-beams did not change the stoichiometry but did enhance the phase separation of the SRO films. Finally, low-energy ion-beam treatment increased the PL intensity and color temperature of SRO/SiO2 superlattices by promoting luminescence from E’ centers. White photoluminescence was thus obtained. This finding will be helpful for development of Si-based light emitters.

Acknowledgment

The authors would like to thank the National Science Council of the Republic of China, Taiwan, for financially supporting this research under Contract No. NSC100-2221-E-006-130-MY2.

References and links

1.

C. K. Tseng, M. C. M. Lee, H. W. Hung, J. R. Huang, K. Y. Lee, J. M. Shieh, and G. R. Lin, “Silicon-nanocrystal resonant-cavity light emitting devices for color tailoring,” J. Appl. Phys. 111(7), 074512 (2012). [CrossRef]

2.

G. R. Lin, Y. H. Pai, C. T. Lin, and C. C. Chen, “Comparison on the electroluminescence of Si-rich SiNx and SiOx based light-emitting diodes,” Appl. Phys. Lett. 96(26), 263514 (2010). [CrossRef]

3.

D. Di, I. Perez-Wurfl, L. Wu, Y. Huang, A. Marconi, A. Tengattini, A. Anopchenko, L. Pavesi, and G. Conibeer, “Electroluminescence from Si nanocrystal/c-Si heterojunction light-emitting diodes,” Appl. Phys. Lett. 99(25), 251113 (2011). [CrossRef]

4.

Y. Berencén, J. Carreras, O. Jambois, J. M. Ramírez, J. A. Rodríguez, C. Domínguez, C. E. Hunt, and B. Garrido, “Metal-nitride-oxide-semiconductor light-emitting devices for general lighting,” Opt. Express 19(S3Suppl 3), A234–A244 (2011). [CrossRef] [PubMed]

5.

N. M. Park, T. S. Kim, and S. J. Park, “Band gap engineering of amorphous silicon quantum dots for light-emitting diodes,” Appl. Phys. Lett. 78(17), 2575–2577 (2001). [CrossRef]

6.

C. C. Tu, Q. Zhang, L. Y. Lin, and G. Cao, “Brightly photoluminescent phosphor materials based on silicon quantum dots with oxide shell passivation,” Opt. Express 20(S1), A69–A74 (2012). [CrossRef] [PubMed]

7.

M. C. Kim, S. Kim, S. H. Choi, and S. Park, “Anomalous light-induced enhancement of photoluminescence from Si nanocrystals fabricated by thermal oxidation of amorphous Si,” Appl. Phys. Lett. 91(3), 033111 (2007). [CrossRef]

8.

C. H. Cheng, Y. C. Lien, C. L. Wu, and G. R. Lin, “Mutlicolor electroluminescent Si quantum dots embedded in SiOx thin film MOSLED with 2.4% external quantum efficiency,” Opt. Express 21(1), 391–403 (2013). [CrossRef] [PubMed]

9.

M. Kulakci, U. Serincan, and R. Turan, “Electroluminescence generated by a metal oxide semiconductor light emitting diode (MOS-LED) with Si nanocrystals embedded in SiO2 layers by ion implantation,” Semicond. Sci. Technol. 21(12), 1527–1532 (2006). [CrossRef]

10.

Y. Ou, V. Jokubavicius, S. Kamiyama, C. Liu, R. W. Berg, M. Linnarsson, R. Yakimova, M. Syväjärvi, and H. Ou, “Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC,” Opt. Mater. Express 1(8), 1439–1446 (2011). [CrossRef]

11.

R. Huang, K. Chen, H. Dong, D. Wang, H. Ding, W. Li, J. Xu, Z. Ma, and L. Xu, “Enhanced electroluminescence efficiency of oxidized amorphous silicon nitride light-emitting devices by modulating Si/N ratio,” Appl. Phys. Lett. 91(11), 111104 (2007). [CrossRef]

12.

J. K. Kim, K. M. Cha, J. H. Kang, Y. Kim, J. Y. Yi, T. H. Chung, and H. J. Bark, “Area-selective formation of Si nanocrystals by assisted ion-beam irradiation during dual-ion-beam deposition,” Appl. Phys. Lett. 85(9), 1595 (2004). [CrossRef]

13.

H. L. Hao, L. K. Wu, and W. Z. Shen, “Controlling the red luminescence from silicon quantum dots in hydrogenated amorphous silicon nitride films,” Appl. Phys. Lett. 92(12), 121922 (2008). [CrossRef]

14.

M. Fukuda, K. Nakagawa, S. Miyazaki, and M. Hirose, “Resonant tunneling through a self-assembled Si quantum dot,” Appl. Phys. Lett. 70(17), 2291–2293 (1997). [CrossRef]

15.

P. Sigmund, “Theory of Sputtering. I. Sputtering Yield of Amorphous and Polycrystalline Targets,” Phys. Rev. 184(2), 383–416 (1969). [CrossRef]

16.

W. Ensinger, “Low energy ion assist during deposition - an effective tool for controlling thin film microstructure,” Nucl. Instrum. Methods Phys. Res. 127–128, 796–808 (1997).

17.

C. C. Lee and S. L. Ku, “Optical and structural properties of SiOx films from ion-assisted deposition,” Thin Solid Films 518(17), 4804–4808 (2010). [CrossRef]

18.

S. S. Zumdahl, Chemistry, 4th ed. (Houghton Mifflin, 1997), chap. 8.

19.

G. R. Lin, C. J. Lin, C. K. Lin, L. J. Chou, and Y. L. Chueh, “Oxygen defect and Si nanocrystal dependent white-light and near-infrared electroluminescence of Si-implanted and plasma-enhanced chemical-vapor deposition-grown Si-rich SiO2,” J. Appl. Phys. 97(9), 094306 (2005). [CrossRef]

20.

H. Nishikawa, E. Watanabe, D. Ito, M. Takiyama, A. Ieki, and Y. Ohki, “Photoluminescence study of defects in ion-implanted thermal SiO2 films,” J. Appl. Phys. 78(2), 842–846 (1995). [CrossRef]

OCIS Codes
(310.0310) Thin films : Thin films
(310.6860) Thin films : Thin films, optical properties

ToC Category:
Thin Films

History
Original Manuscript: May 10, 2013
Revised Manuscript: June 13, 2013
Manuscript Accepted: June 19, 2013
Published: June 25, 2013

Citation
Chuan-Feng Shih, Chu-Yun Hsiao, and Kuan-Wei Su, "Enhanced white photoluminescence in silicon-rich oxide/SiO2 superlattices by low-energy ion-beam treatment," Opt. Express 21, 15888-15895 (2013)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-21-13-15888


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References

  1. C. K. Tseng, M. C. M. Lee, H. W. Hung, J. R. Huang, K. Y. Lee, J. M. Shieh, and G. R. Lin, “Silicon-nanocrystal resonant-cavity light emitting devices for color tailoring,” J. Appl. Phys.111(7), 074512 (2012). [CrossRef]
  2. G. R. Lin, Y. H. Pai, C. T. Lin, and C. C. Chen, “Comparison on the electroluminescence of Si-rich SiNx and SiOx based light-emitting diodes,” Appl. Phys. Lett.96(26), 263514 (2010). [CrossRef]
  3. D. Di, I. Perez-Wurfl, L. Wu, Y. Huang, A. Marconi, A. Tengattini, A. Anopchenko, L. Pavesi, and G. Conibeer, “Electroluminescence from Si nanocrystal/c-Si heterojunction light-emitting diodes,” Appl. Phys. Lett.99(25), 251113 (2011). [CrossRef]
  4. Y. Berencén, J. Carreras, O. Jambois, J. M. Ramírez, J. A. Rodríguez, C. Domínguez, C. E. Hunt, and B. Garrido, “Metal-nitride-oxide-semiconductor light-emitting devices for general lighting,” Opt. Express19(S3Suppl 3), A234–A244 (2011). [CrossRef] [PubMed]
  5. N. M. Park, T. S. Kim, and S. J. Park, “Band gap engineering of amorphous silicon quantum dots for light-emitting diodes,” Appl. Phys. Lett.78(17), 2575–2577 (2001). [CrossRef]
  6. C. C. Tu, Q. Zhang, L. Y. Lin, and G. Cao, “Brightly photoluminescent phosphor materials based on silicon quantum dots with oxide shell passivation,” Opt. Express20(S1), A69–A74 (2012). [CrossRef] [PubMed]
  7. M. C. Kim, S. Kim, S. H. Choi, and S. Park, “Anomalous light-induced enhancement of photoluminescence from Si nanocrystals fabricated by thermal oxidation of amorphous Si,” Appl. Phys. Lett.91(3), 033111 (2007). [CrossRef]
  8. C. H. Cheng, Y. C. Lien, C. L. Wu, and G. R. Lin, “Mutlicolor electroluminescent Si quantum dots embedded in SiOx thin film MOSLED with 2.4% external quantum efficiency,” Opt. Express21(1), 391–403 (2013). [CrossRef] [PubMed]
  9. M. Kulakci, U. Serincan, and R. Turan, “Electroluminescence generated by a metal oxide semiconductor light emitting diode (MOS-LED) with Si nanocrystals embedded in SiO2 layers by ion implantation,” Semicond. Sci. Technol.21(12), 1527–1532 (2006). [CrossRef]
  10. Y. Ou, V. Jokubavicius, S. Kamiyama, C. Liu, R. W. Berg, M. Linnarsson, R. Yakimova, M. Syväjärvi, and H. Ou, “Donor-acceptor-pair emission characterization in N-B doped fluorescent SiC,” Opt. Mater. Express1(8), 1439–1446 (2011). [CrossRef]
  11. R. Huang, K. Chen, H. Dong, D. Wang, H. Ding, W. Li, J. Xu, Z. Ma, and L. Xu, “Enhanced electroluminescence efficiency of oxidized amorphous silicon nitride light-emitting devices by modulating Si/N ratio,” Appl. Phys. Lett.91(11), 111104 (2007). [CrossRef]
  12. J. K. Kim, K. M. Cha, J. H. Kang, Y. Kim, J. Y. Yi, T. H. Chung, and H. J. Bark, “Area-selective formation of Si nanocrystals by assisted ion-beam irradiation during dual-ion-beam deposition,” Appl. Phys. Lett.85(9), 1595 (2004). [CrossRef]
  13. H. L. Hao, L. K. Wu, and W. Z. Shen, “Controlling the red luminescence from silicon quantum dots in hydrogenated amorphous silicon nitride films,” Appl. Phys. Lett.92(12), 121922 (2008). [CrossRef]
  14. M. Fukuda, K. Nakagawa, S. Miyazaki, and M. Hirose, “Resonant tunneling through a self-assembled Si quantum dot,” Appl. Phys. Lett.70(17), 2291–2293 (1997). [CrossRef]
  15. P. Sigmund, “Theory of Sputtering. I. Sputtering Yield of Amorphous and Polycrystalline Targets,” Phys. Rev.184(2), 383–416 (1969). [CrossRef]
  16. W. Ensinger, “Low energy ion assist during deposition - an effective tool for controlling thin film microstructure,” Nucl. Instrum. Methods Phys. Res.127–128, 796–808 (1997).
  17. C. C. Lee and S. L. Ku, “Optical and structural properties of SiOx films from ion-assisted deposition,” Thin Solid Films518(17), 4804–4808 (2010). [CrossRef]
  18. S. S. Zumdahl, Chemistry, 4th ed. (Houghton Mifflin, 1997), chap. 8.
  19. G. R. Lin, C. J. Lin, C. K. Lin, L. J. Chou, and Y. L. Chueh, “Oxygen defect and Si nanocrystal dependent white-light and near-infrared electroluminescence of Si-implanted and plasma-enhanced chemical-vapor deposition-grown Si-rich SiO2,” J. Appl. Phys.97(9), 094306 (2005). [CrossRef]
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