Raman monitoring of ZnSe and ZnSxSe1−x nanocrystals formed in SiO2 by ion implantation

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Abstract

Structural and optical properties of SiO2 (600 nm)/Si films successively implanted with two types of ions (Zn and Se) or three types of ions (Zn, Se and S) and afterwards annealed at 900 °C were investigated. RS, PL and TEM methods were used to characterize A2B6 nanocrystals synthesized in SiO2 matrix. The Raman spectra recorded using an excitation with two different laser lines (355 and 473 nm) have shown the formation of ZnSe nanocrystals after a double implantation of Zn and Se ions, while ZnSxSe1−x nanoclusters have been synthesized after a triple implantation of Zn, Se and S ions. Based on Raman spectra recorded with blue and UV excitations, the possible sulfur content (x ≈ 0.4) has been estimated for synthesized ternary alloy. The intensive PL bands for SiO2 films implanted with (Zn, Se, S) and (Zn, Se) were detected in the blue and red spectral ranges, respectively.

Introduction

Nowadays, synthesis and characterisation of A2B6 semiconductors have attracted considerable attention due to its application potential. Among A2B6 materials, the nanostructured ZnS and ZnSe are regarded as promising materials for light-emitting diodes, flat panel displays, infrared windows, nonlinear optical devices, lasers, photocatalysts and sensors. There is a particular interest in ternary alloys ZnSxSe1−x due to the possibility of variation of band gap and lattice constant with the composition of the alloys. Besides, ZnSxSe1−x is considered as a future material in the production of biomedical labels, output couplers, lenses and optically controlled switches.

There are many methods to prepare ZnSe, ZnS and ZnSxSe1−x nanocrystals (NCs) such as molecular-beam epitaxy [1], [2], surfactant-assisted chemistry, sonochemical method, solvothermal route, chemical vapor deposition, solid state thermal reaction between Zn and S or Se powders [3], thermal evaporation [4], sulfur/selenization annealing of Zn precursors [5], organometallic synthesis [6], atomic layer epitaxy, metalorganic chemical vapor deposition, pulsed laser deposition [7], RF magnetron sputtering [8]. High-fluence ion implantation was demonstrated as a promising method to create A2B6 nanocrystals in SiO2 matrix [9], [10], [11]. This technique is completely compatible with current silicon technology. It was successfully used for a synthesis of monoelemental metallic and semiconductors clusters as well as binary alloys such as group’s IV precipitates (SiGe, SiC) [12], A3B5 nanocrystals (InAs, GaSb, InSb, GaN) [13], [14], [15], [16], [17], oxides (SnO2) [18] and silicides [19]. It is expected that this technique allows the formation of ternary alloys or even core/shell structures [20], [21]. As far as we know, up to now there are no reports in the literature devoted to ion-beam synthesis of ZnSe and ZnSxSe1−x nanocrystals in SiO2 layers except a brief mention of a possibility of ZnSe creation in a-SiO2 in Ref. [22]. In the present work, the attempt of ZnSe, ZnSxSe1−x and core (ZnSe)/shell (ZnS) nanostructures synthesis in SiO2 matrix by ion implantation is reported. For this purpose we have studied structural and optical properties of SiO2 films after double ion implantation (Zn, Se) and triple ion implantation (Zn, Se, S) followed by thermal annealing.

Section snippets

Experimental

The energies of implantations have been chosen on the basis of TRIM simulation in order to achieve maximum concentrations of Zn, Se, S impurities at about the same depth. The implantations were carried out into SiO2 (600 nm)/Si structures at 500 °C. Two sets of the samples were prepared. The first set (samples A) was implanted with Zn and Se ions. The samples of the second set (samples B) were implanted with Zn, Se and S ions. The implanted species order was conditioned by an attempt to create

Results and discussion

Fig. 1 shows the bright-field XTEM images of precipitates formed after ion implantation followed by furnace annealing in the samples A and B. The results of TEM investigation revealed the inhomogeneous size and depth distribution of synthesized nanoclusters in silicon oxide matrix. In Fig. 1, it is observed three characteristic layers in the implanted films. The first near-surface layer (10–60 nm) contains many small clusters with the sizes of 5–10 nm (arrows 1). The second layer (60–180 nm)

Conclusion

In conclusion, the phase and structural compositions of the SiO2 (600 nm)/Si films after double (Zn and Se) and triple (Zn, Se, S) ion implantation followed by annealing were characterized by RS spectroscopy and XTEM characterisation, respectively. The synthesis of ZnSe nanocrystals in the silicon dioxide films after double implantation with (Zn and Se) ions and annealing was confirmed by RS spectra. In the case of triple implantation (Zn, Se, S) with subsequent annealing, the presence of ZnSe,

Acknowledgment

This research was partly supported by the Belarusian Republican Foundation for Fundamental Research, grant No. F17M-053.

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