T. Tsvetkova

Ion implantation induced modification of a-SiC : H

Abstract Optical transmission measurements have been carried out on thin a-SiC:H alloy films, implanted with ions of group IV elements. High doses of the order of 1017 cm−2 have been used leading to a considerable shift of the absorption edge to lower photon energies. This shift may be attributed both to additional defect introduction and to accompanying formation of bonds between implanted ions and the atoms of the alloy, as confirmed by IR and Raman measurements. The observed chemical modification results from the high concentration of introduced atoms which is of the order of those for the host elements.

Surface morphology changes in ion implanted chalcogenide films after annealing

Abstract Here we report some results of ion implantation and annealing effects on the surface morphology of thin amorphous films of materials in the Asue5f8Se system. Ion implantation with different gaseous ions (Ar+, N+ and O+) and subsequent annealing have been performed leading to a change in the thin film morphology and the measured optical properties. Optical and electronic microscope photographs are presented showing details of the rippled film surface. The influence of different types of substrates on the frost pattern formation is demonstrated and a possible mechanism ion the observed effects is discussed.

Study of the ion implantation of 119Sn in a-Si1−xCx:H

The Mossbauer spectroscopy and Rutherford backscattering spectroscopy studies presented here allow an investigation of the origins of the previously observed changes in optical absorption in sputter deposited a-Si1-xCx:H films caused by high dose Sn implantations. To this end, we investigate the microscopic surroundings and the bonding structures of the Sn atoms. At doses up to 1 x 10(17) cm(-2) a major fraction of Sn takes a quasi-substitutional site, sp(3) bonded to four Si neighbours, while a smaller fraction is present as Sn2+, presumably due to SnO formation. The latter fraction increases at the higher doses and the increase is paralleled by the formation of Sn4+ and a prominent metallic sn component. This beta-Sn fraction, presumably in the form of nanosized precipitates, becomes dominant at the higher doses, thus explaining the complete lack of optical transmission

Vibrational spectroscopy of Ga+ ion implanted ta-C films

In the present work, low energy Ga+ ion beam implantation was used for the structural and optical properties modification of tetrahedral amorphous carbon (ta-C) thin films, using gallium (Ga+) as the ion species. Thin film samples (d~40nm) of ta-C, deposited by filtered cathodic vacuum arc (FCVA), have been implanted with Ga+ at ion energy E = 20 keV and ion doses D=3.1014÷3.1015 cm-2. The Ga+ ion beam induced structural modification of the implanted material results in a considerable change of its optical properties, displayed in a significant shift of the optical absorption edge to lower photon energies as obtained from optical transmission measurements. This shift is accompanied by a considerable increase of the absorption coefficient (photo-darkening effect) in the measured photon energy range (0.5÷3.0 eV). These effects could be attributed both to additional defect introduction and increased graphitisation, as well as to accompanying formation of bonds between the implanted ions and the host atoms of the target, as confirmed by infra-red (IR) and Raman measurements. The optical contrast thus obtained (between implanted and unimplanted film material) could be made use of for information archiving, in the area of high-density optical data storage, while using focused Ga+ ion beams.

Modification of the electronic properties of a-Si 1-x C x :H by Fe + ion implantation

The electrical and optical properties of hydrogenated amorphous silicon-carbide alloy films (a-Si 1-x C x :H), modified by Fe + ion implantation (D = 1×10 16 - 1×10 17 cm -2 ), have been investigated. Optical transmission spectra have been measured in the visible range (400-900 nm) and considerable absorption edge shift to the longer wavelength region has been registered, together with well-defined decrease of transmittance in the whole measured range. These effects are increased with the dose and are similar for samples with different carbon content (x 1 =0.08 and x 2 =0.15). Room temperature (RT) surface electrical conductivity is also increased by Fe + implantation and the effect is most pronounced for the highest doses (D ~ 10 17 cm -2 ). The temperature dependence of the conductivity was measured in the temperature range from RT to 250 o C. The activation energy is considerably reduced and the effect is again strongest for the highest doses. From the above results we conclude that high doses Fe + implantation in a-Si 1-x C x :H affects both the localised states deep in the gap and the shallow states in the band tails.