Erbium enhanced formation and growth of photoluminescent Er/Si nanocrystals
Introduction
Erbium doped silicon nanocrystals provide a promising route to obtain energy-efficient photoluminescence (PL) at 1.54 μm (emission due to 4I13/2 → 4I15/2 transition in Er3 +) [1], [2], [3], [4], [5], [6]. Due to the minimal signal attenuation in commercial optical fibers, 1.54 μm light is of high interest for photonic communication. In contrast with the direct excitation of Er in most materials, this wavelength can be generated very specifically and much more efficiently using Er doped Si nanocrystal assemblies. In this case, the transfer of energy from the Si nanocrystals to Er compensates the small cross section (10- 21 cm2) of Er ions [7].
One of the more popular techniques to grow pure Si nanocrystals is thermal treatment of sputtered Si suboxide (SiOx) thin films [8], [9], [10]. Alternative techniques are, co-sputtering from Si/SiO2 targets [11], deposition of SiO/SiO2 multilayers [12] and sputtering from a SiO2 target in a reducing atmosphere [13].
Er dopage of the Si nanocrystals is most often achieved by ion implantation into pre-formed Si nanocrystals after thermal treatment [14], [15]. Although this technique requires a secondary thermal treatment to recover implantation damage suffered by the nanocrystals, it is preferred over Er/SiOx deposition by Plasma Enhanced Chemical Vapor Deposition (PECVD), where difficulties are encountered due to the low vapor pressure of erbium compounds [16]. To overcome the problems associated with ion implantation and PECVD, an alternative method for the preparation of Er doped thin films of SiOx has been presented a few years ago. Co-sputtering of Er and Si atoms using a silicon target covered with pieces of metallic erbium in a reactive atmosphere results in thin films of Er doped SiOx. Upon annealing, these films directly yield Er/Si nanocrystal assemblies [17].
Er3 + luminescence at 1.54 μm is strongly dependent on the local coordination of Er [18], [19]. In the case of isolated ions, the luminescence intensity is very low because the electric dipole transitions between the initial and final states are forbidden. When the ions occupy non-symmetric positions in a framework, the local environment of the ions not only influences the shape of the spectrum, but also the PL intensity because the transitions become partially allowed due to mixing of states of opposite parity [20].
This work describes and explains the influence of co-sputtered Er in SiOx thin films on Si nanocrystal nucleation and growth during thermal treatment and the self organization into a highly efficient Si-nanocrystal/Er photoluminescent composite.
Section snippets
Experimental section
Er doped SiOx thin films (~ 1.0 μm thickness) were prepared by RF-sputtering in a modified Leybold 400 system. The single target consisted of a 75 mm diameter 99.999% Si block partially covered with pieces of metallic Er (~ 4 mm2, thickness ~ 1000 μm). During sputtering the sputtering chamber was flushed with an Ar + O2 electronic grade (99.999%) gas mixture. The base pressure of the system was always kept below 2.5 × 10− 4 Pa using a turbo-molecular pump. While the Ar flux was controlled to keep the
Results and discussion
The area of the Er sheets mounted on the silicon target during co-sputtering determines the final concentration of Er in the resulting silicon suboxide thin films (see Fig. 1). Fig. 2 shows HRTEM images representative for three samples sputtered on Si < 111 > using 5.5 × 10− 3 Pa of partial oxygen pressure with different Er concentration and annealed at 1150 °C. Based on the selected area electron diffraction patterns the observed nanocrystals can be identified as Si crystallites with different
Conclusions
In summary, this report demonstrates the feasibility of producing silicon nanocrystal/Er assemblies by reactive RF-sputtering using a single Si target covered with small pieces of metallic Er. The nanocrystal size and density after annealing are highly correlated to the Er concentration in the original suboxide thin films, indicating Er centers promote the nucleation of Si nanocrystals. At annealing temperatures below 1100 °C, the uniformly distributed Er centers scavenge mobile oxygen atoms,
Acknowledgements
The authors acknowledge Prof. Manfredo Tabakniks for help with the RBS measurements, Prof. Horst Strunk and Dr. Ines Häusler for support with HRTEM. This work was partially supported by FAPESP, PROBRAL CAPES/DAAD and LNLS – National Synchrotron Light Laboratory, Brazil. E.B. acknowledges a fellowship as Postdoctoraal onderzoeker van FWO-Vlaanderen. C.E.A.K and J.A.M acknowledge the Flemish Government for long-term structural funding (Methusalem).
References (37)
- et al.
J. Lumin.
(2000) - et al.
J. Non-Cryst. Solids
(2002) - et al.
Thin Solid Films
(2011) - et al.
J. Non-Cryst. Solids
(2002) - et al.
Nucl. Instr. Meth. B
(2011) - et al.
Appl. Phys. Lett.
(2000) - et al.
Nano Lett.
(2001) - et al.
Appl. Phys. Lett.
(2003) - et al.
J. Vac. Sci. Technol. B
(2009) - et al.
Appl. Phys. Lett.
(2005)
Phys. Rev. B
Nanotechnology
Jpn. J. Appl. Phys.
Appl. Phys. Lett.
J. Appl. Phys.
Appl. Phys. Lett.
J. Light. Technol.
Opt. Mat.
Cited by (12)
Tailoring Stark effect in the 1.54 µm emission of Er-doped ZnO thin films
2021, Scripta MaterialiaSynthesis, characterization and Judd-Ofelt analysis of Sm <sup>3+</sup> -doped anhydrous Yttrium trimesate MOFs and their Y <inf>2</inf> O <inf>3</inf> :Sm <sup>3+</sup> low temperature calcination products
2019, Journal of LuminescenceCitation Excerpt :Sm3+ ([Xe] 4f5) has an odd number of electrons in the 4f subshell and, according to Kramer's rule, their energy eigenstates are at least doubly degenerate in any ligand field. Therefore, the odd number of electronic configuration will unfold in a maximum of (J + 1/2) Stark-components [23–27]. Sm3+-doped compounds exhibit orange emission under excitation of ultraviolet radiation.
High Er<sup>3+</sup> luminescent efficiency in Er-doped SiO<inf>x</inf> films containing amorphous Si nanodots
2016, Journal of Alloys and CompoundsCitation Excerpt :Usually, the as-deposited samples need to be post-heated to form the sensitizers, such as amorphous or crystalline Si nanodots. It is interesting that the Er3+ photo-luminescence (PL) behavior strongly depends on the post-annealing temperatures: The Er3+ PL intensity increases with annealing temperature in the beginning, however, drops dramatically when the temperature is above 1000 °C [11,12]. Although some previous works have claimed that the annealing temperature dependence could be due to the nature of the sensitizers (including crystallinity, density, and size etc.) and/or to the chemical environment surrounding the Er3+ ions which could affect the energy transfer and energy decay dynamics of them, it has been difficult to identify which of the two aspects dominates the annealing temperature dependence [11,13].
Co-mediated nucleation of erbium/silicon nanoclusters in fused silica
2015, Journal of Materials ResearchFormation of silicon nanocomposites by annealing of (SiO<inf>x</inf>/Sm)<inf>n</inf> multilayers: luminescence, Raman and FTIR studies
2023, Applied Nanoscience (Switzerland)Samarium-induced enhancement of SiO<inf>x</inf> decomposition and Si nanocrystals formation
2023, Applied Nanoscience (Switzerland)