Photoluminescence in silicon/silicon oxide films produced by the Pulsed Electron Beam Ablation technique

https://doi.org/10.1016/j.jnoncrysol.2011.12.072Get rights and content

Abstract

In this work we report studies of the photoluminescence emission in samples based on Si/SiOx films deposited by the Pulsed Electron Beam Ablation (PEBA) technique. The samples were prepared at room temperature using targets with different Si/SiO2 concentrations. The samples were characterized using X-ray Absorption Edge Spectroscopy (XANES) at the Si―K edge, Raman spectroscopy, Photoluminescence (PL) and X-ray Photoelectron Spectroscopy (XPS). The concentration of a-Si and nc-Si in the film was dependent on the silicon concentration in the target. It was also observed that the PL is strongly dependent on the structural amorphous/crystalline arrangement.

Highlight

► Structural analysis of SiOx films deposited by the Pulsed Electron Beam Ablation. ► This technique produces films at room temperature. ► It produced Si-rich SiOx films using targets made of Si/SiO2 powder mixtures. ► Photoluminescence was obtained as result at visible range.

Introduction

The photoluminescence in silicon nanoparticles has been widely studied since the discovery of bright emission in porous silicon at room temperature in the 1990s [1]. One area of application of these nanoparticles is in optoelectronic devices due to the possibility of producing optical and electronic devices using the current silicon-based technology, hence greatly reducing manufacturing costs and the problems arising in the integration of optical and microelectronic devices [2]. The challenge to use silicon as an emitter device is to produce tunable PL in the entire visible range [3]. Several techniques have been employed to obtain silicon nanoparticles, such as sputtering [4], [5], [6], evaporation [7], [8], PECVD [2], [9], ionic implantation [10], among others. In general, these techniques produce a silicon-rich material by deposition or growth followed by annealing at high temperature to form silicon nanoparticles [2]. However, the high temperature works against the integration with electronic devices due to the diffusion of dopants [11].

In this work, Si nanoparticles were produced by the PEBA technique. This technique presents some advantages compared to UV-laser ablation such as low deposition cost, good thickness control, possibility of producing films of complex stoichiometry (such as high-Tc superconductors, intermetallic alloys and glasses), the absence of the dangerous gasses pervading CVD techniques [12], and low deposition temperature. This technique is a process in which a high power electron beam (15–20 KV) is pulsed producing the volatilization of the impacted region of the material. In this work we study the formation of silicon clusters in the film and the influence of the deposition process on the photoluminescence.

Section snippets

Experimental

We prepared targets for the PEBA technique starting from powder mixtures of silicon dioxide 99.5% metal basis and silicon 99.5%, crystalline, both − 325 mesh in size (Alfa Aesar). Three Si:SiO2 powder ratios were used, as shown in the Table 1. After mixing, the powders were compacted by a press and sintered in argon ambient at 1100 °C.

Before the deposition, the deposition chamber was pumped to 0.01 Pa, while the PEBA process was performed under Argon, at 1.33 Pa approximately. The current was fixed

Results

XPS analyses were performed in the targets after sintering and in the deposited films. The Si 2p level spectra for the three as-prepared targets are presented in Fig. 1. The target with the higher SiO2 concentration, S12, (Fig. 1a) presents a clear separation between Si4 + (associated to SiO2) and Si0 (associated to metallic Si). A small amount of the Si2 + oxidation state can also be observed, indicating a weak reaction of the powders during sintering.

The S11 target with the equal concentrations

Discussion

The phase separation and the small size of the silicon clusters are responsible for the optical modifications of the photoluminescence of silicon based films, and Raman spectroscopy has shown to be very sensitive to the local atomic arrangement in the study of those films [14], [15].

The shape of the spectrum permits to evaluate the presence of silicon excess dispersion in the samples. It is observed that the amount of redshift and linewidth broadening of the Raman line depends on the silicon

Conclusion

We have shown the possibility of controlling the PL emission by changing the chemical composition of the targets. It was possible to obtain different structural arrangement in the film, as nc-Si, amorphous silicon, and consequently, different PL emission, using the PEBA technique at room temperature. From the structural point of view, all samples can be thought as a composite material in which the size and density of the silicon clusters as well the Si-nc embedded in the SiOx matrix are

Acknowledgments

The authors are grateful to the Laboratório de Espectroscopia Molecular at IQUSP for Raman spectra and to the Brazilian Synchrotron Light Laboratory—LNLS at the SXS line for XANES spectra. The authors are also grateful to the Chilean agency CONICYT for the financial support (Grant no. 11085026).

References (25)

  • T. Creazzo et al.

    J. Lumin.

    (2010)
  • Q. Ma et al.

    J. Lumin.

    (2011)
  • Y. So et al.

    Thin Solid Films

    (2011)
  • Z. Xia et al.

    Solid State Commun.

    (2010)
  • A. Keffous et al.

    Appl. Surf. Sci.

    (2010)
  • B. Choi et al.

    Surf. Coat.Technol.

    (2007)
  • I. Bineva et al.

    J. Lumin.

    (2007)
  • A. Bacıoglu et al.

    J. Lumin.

    (2010)
  • A. Morales-Sánchez et al.

    Mater. Sci. Eng. B

    (2010)
  • F. Teixeira et al.

    Sol. Energy

    (2005)
  • M. Ribeiro et al.

    Thin Solid Films

    (2003)
  • T.V. Torchynska et al.

    J. Non-Cryst. Solids

    (2006)
  • Cited by (0)

    View full text