N. Bibić

Direct synthesis of β-FeSi2 by ion beam mixing of Fe/Si bilayers

Abstract.The iron di-silicide β-FeSi2 is a promising direct band gap semiconductor but difficult to produce. Here, the successful direct synthesis of this phase by ion beam mixing of Fe/Si bilayers at temperatures in the range of 450 to 550xa0°C is reported. The obtained single-phase β-FeSi2 layers and their structure are confirmed by Rutherford backscattering spectrometry, X-ray diffraction and conversion electron Mössbauer spectroscopy.

Interface mixing in Ta/Si bilayers with Ar ions

Abstract We report on the room-temperature synthesis of the low-resistivity TaSi2 phase using ion-beam mixing of Ta/Si bilayers with Ar ions. The formation of the silicide phase is observed for different damage energies deposited at the Ta/Si interface. The variance Δσ 2 of the reacted (TaSi2) layer thickness varies linearly with the ion fluence Φ and the reaction rate Δσ 2 /Φ is proportional to the deposited damage energy density FD. The measured mixing/reaction efficiency, Δσ 2 /ΦF D =10±1 nm5/keV, is in agreement with the value calculated by the model of compound formation under local thermal spikes.

Synthesizing single-phase β-FeSi2 via ion beam irradiations of Fe/Si bilayers

Abstract This paper presents results on the direct synthesis of the β-FeSi 2 phase by ion beam mixing of Fe/Si bilayers with Xe ions. The influence of the substrate temperature, ion fluence and energy on the growth of this phase was investigated using Rutherford backscattering (RBS), X-ray diffraction (XRD) and conversion electron Mossbauer spectroscopy (CEMS). Complete growth of single-phase β-FeSi 2 was achieved by 205 keV Xe ion irradiation to a fluence of 2×10 16 ions / cm 2 at 600°C. We propose a two-step reaction mechanism involving thermal and ion beam energy deposition.

Ion beam mixing in Fe/Si and Ta/Si bilayers: Possible effects of ion charges

Abstract Thin Fe and Ta layers of 30–45 nm thickness, deposited via magnetron sputtering on Si (1xa00xa00) substrates, were bombarded at room temperature with 100 keV Ar 1+ or Ar 8+ or with 250 keV Xe 1+ or Xe 19+ ions in order to test the influence of the ion charge state on the surface sputtering and interface mixing. The samples were characterized by means of Rutherford backscattering at 0.9–3.0 MeV α-particle energy, time-of-flight elastic recoil detection analysis with a 53 MeV 127 I 10+ beam and atomic force microscopy. No influence of the charge state on the sputtering and athermal mixing rate was observed in the case of the Ta/Si system. However, in the case of the Fe/Si system, the ion charge was observed to have an influence on the mixing rate.

Xenon ion beam mixing in Ni3N/Al bilayers

Abstract The effects of Xe irradiations on surface and interface modifications of Ni3N/Al bilayers deposited via de (reactive) sputtering on silicon substrates were investigated. The 250–1000 keV Xe irradiations were performed at RT and at fluences of 0.5-2×1016 ions/cm2. The samples were analyzed via Rutherford backscattering with 900 keV α-particles. The mixing rates k were found to depend strongly on the R p d ratio, where Rp denotes the mean ion range and d the film thickness; the maximum mixing observed was 2.9(2) nm4. This high k-value is compared with Monte Carlo calculations of ballistic mixing and experiments on Xe-mixed Cr2N and TiN films on several substrates. Effects of the chemical binding in the various compounds are discussed.

Structural and optical properties of β-FeSi2 layers grown by ion beam mixing

Abstract This study deals with structural and optical properties of β-FeSi 2 layers produced by direct ion beam mixing of Fe/Si bilayers with Xe ions. By irradiation of 35 nm Fe on Si, at 600 °C with 205 keV Xe to 2×10 16 ions/cm 2 , the formation of ∼105 nm single-phase β-FeSi 2 layers was achieved. Their structures were analyzed by Rutherford backscattering spectroscopy, X-ray diffraction, conversion electron Mossbauer spectroscopy, high resolution transmission electron microscopy, and photo-absorption. The structural analyses revealed that the β-FeSi 2 layers grow in the form of irregularly shaped crystal grains, with a pronounced surface morphology, but with a rather sharp silicide/silicon interface. The grains that originate from the interface are epitaxially oriented relative to the Si(100) substrate. Optical absorption, as compared with that in β-FeSi 2 layers produced by ion beam synthesis or co-sputter deposition, indicates a direct band gap of 0.92 eV. A pronounced surface roughness of the ion beam mixed layers yielded photo-absorption approximately three times higher as compared with the other two sets of samples. The band gap stays nearly constant over the temperature range from 80 to 295 K. This is tentatively assigned to a high degree of structural disorder and stress induced in the ion beam mixed β-FeSi 2 layers.

Mixing and Silicide Formation during Xe-Ion Beam Irradiations of Ta/Si Bilayers

Thin Ta layers deposited on Si (100) substrates were irradiated with 475 keV Xe + ions to fluences of (0.5-2) × 10 16 ions/cm 2 at temperatures between room temperature and 400 °C. By means of Rutherford Backscattering Spectrometry, the interface mixing and tantalum silicide formation were monitored as function of the ion fluence. TaSi 2 phase formation was verified using X-ray diffraction. The interface broadening variance was found to depend linearly on the ion fluence and was explained with the help of a compound formation model involving global thermal spikes.

Effects of the Ar ions pre‐amorphization of Si substrateon interface mixing of Fe/Si bilayers

Ion beam mixing of Fe/Si bilayers, induced by 100 keV 40Arions at room temperature was investigated. Rutherford backscattering spectroscopy (RBS), atomic force microscopy (AFM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were applied for structural characterization. The main focus of this study was on the influence of the substrate structure on interface mixing. The influence of the substrate structure is due to the two classes of irradiated bilayers, Fe thin films deposited on crystalline or pre‐amorphized Si substrates. An about 76% higher efficiency of atomic transport across the pre‐amorphized Fe/a‐Si interface as compared to that of Fe/c‐Si bilayers was observed.

Mössbauer Optimization of the Direct Synthesis of β-FeSi2 by Ion Beam Mixing of Fe/Si Bilayers

At present, there is an increasing interest in the iron di-silicide phase β-FeSi2, which is supposed to be a direct band gap semiconductor and one of the most promising materials for silicon-based optoelectronics, e.g., light-emitting devices, solar cells, and photo detectors. But this phase is very difficult to be produced. Here, the successful direct synthesis of this phase by ion beam mixing of Fe/Si bilayers at temperatures in the range of 400 to 600°C is reported. The aim of the experiments was to achieve a complete reaction of the deposited Fe layer with the Si substrate that results in the formation of a pure, single-phased β-FeSi2 surface layer. The obtained silicide layers, their structure and composition are investigated by conversion electron Mossbauer spectroscopy (CEMS), Rutherford backscattering spectrometry (RBS), and X-ray diffraction (XRD). The fraction of the β-FeSi2 formed is determined by CEMS as function of ion species, energy, fluence and temperature. Complete growth and formation of a single-phased β-FeSi2 layer was achieved by 205 keV Xe ion irradiation at a fluence of 2 × 1016 ions/cm2 at 600°C.