O. Valassiades

Combined electrical and mechanical properties of titanium nitride thin films as metallization materials

Titanium nitride (TiNx) thin films, ∼100 nm thick, were deposited on Si(100) substrates by dc reactive magnetron sputtering. The effects of the substrate bias voltage and deposition temperature on their optical, electrical, and mechanical properties have been studied. It was found a strong correlation between the electrical and mechanical properties of the films which are significantly improved with increasing the substrate bias voltage and the deposition temperature. The low resistivity (43 μΩ cm), combined with the high hardness and elastic modulus values, suggest the TiNx as a promising metallization material in Si technology.

Infrared spectroscopic and electronic transport properties of polycrystalline semiconducting FeSi2 thin films

Polycrystalline semiconducting FeSi2 thin films were grown on (100) Si substrates of high resistivity by electron beam evaporation of amorphous Si/Fe ultrathin multilayers in an ultrahigh vacuum system, followed by conventional vacuum furnace (CF) or rapid thermal annealing (RTA). Infrared reflectance and transmittance measurements were employed for optical characterization of the samples at room temperature. The results indicate a direct transition at about 0.85 eV, an indirect transition at about 0.79 eV, and exponential band tail states within the band gap. The quality of the silicide is improved by increasing the annealing temperature from 600 to 800 °C in the RTA process, while the opposite is observed in the CF annealed samples. Transport measurements were performed on a typical β‐FeSi2 layer of high quality grown by CF at low temperature. The measured mobility is about 97 cm2/V s and the hole concentration is about 1×1017 cm−3. The mobility is a factor of 10 higher and the hole concentration a fact...

The Meyer–Neldel rule in the conductivity of polycrystalline semiconducting FeSi2 films

The electrical transport properties of polycrystalline semiconducting β-FeSi2 films have been evaluated by conductivity (σ) measurements over the temperature range 50–300 K. At low temperatures (T<200 K), a variable range hopping conduction was observed, from which the number of states near the Fermi level and the degree of disorder in the material were obtained. At moderate temperatures (200–300 K), the ln σ vs 103/T curves show anomalous features such as kinks or continuous bending. In this temperature range, the conductivity data satisfy the Meyer–Neldel rule, (MNR), which is of fundamental importance for the transport properties of the β-FeSi2. The results show that the MNR parameters are related with the degree of disorder in the material.

Optical and electrical characterization of high quality β-FeSi2 thin films grown by solid phase epitaxy

Abstract High quality β-FeSi 2 thin films were grown on Si〈100〉 substrates by UHV electron beam evaporation of α-Si/Fe multilayers and annealed by conventional vacuum furnace and rapid thermal techniques. Infrared spectroscopy (reflectance and transmittance) and electrical measurements were employed to characterize the films. Hall measurements performed on the thin films yielded exceptionally high free carrier mobilities, up to 112 cm 2 /Vs.

Influence of conventional furnace and rapid thermal annealing on the quality of polycrystalline β-FeSi2 thin films grown from vapor-deposited Fe/Si multilayers

Thin films of polycrystalline β-FeSi2 were grown on (100) Si substrates of high resistivity by electron beam evaporation of Si/Fe ultrathin multilayers and subsequent annealing by conventional vacuum furnace (CVF) and rapid thermal annealing (RTA) for 1 h and 30 s, respectively, in the temperature range from 600 to 900°C. X-ray diffraction, Raman spectroscopy, spectroscopic ellipsometry, resistivity and Hall measurements were employed for characterization of the silicide layers quality in terms of the annealing conditions. For the silicide layers prepared by CVF annealing, although the grain size increase with increasing the annealing temperature, the optimum temperature to obtain the higher material quality (carrier mobility of the order of 100 cm2 Vs−1 and carrier concentration of about 1 × 1017 cm−3) is about 700°C. At higher annealing temperatures, the quality of the material is degraded due to the presence of the oxide Fe2O3. In the case of the silicides prepared by RTA, the quality of the material is improved progressively with increasing the annealing temperature up to 900°C.

Structural and giant magnetoresistance characterization of AgCo multilayers

Abstract Ag Co multilayers were prepared on various substrates (Si, polyimide and glass) by e-beam evaporation under ultra high vacuum. X-ray diffraction and high resolution electron microscopy studies showed a deterioration of multilayer structure upon reducing the individual Co-layer thickness to 0.5 nm. Furthermore, the saturation field in the parallel field geometry increases, as SQUID magnetometry revealed, while magnetoresistance reaches 16% at room temperature and exceeds 30% at 30 K. Magnetoresistance values were found to depend strongly on individual layer thicknesses as well as on the total film thickness.

Giant magnetoresistance response in Ag–Co multilayers and nanoparticles

Abstract Ag–Co multilayers with very thin Co layers exhibit self-organized nanogranular structure and large values of giant magnetoresistance (GMR). In this work, a third non-magnetic element X (X=Cu, Pt, Si) is added to the Ag layer and the influence of this modification on the structural, magnetic and magnetotransport properties of the samples is examined. We find that the addition of Cu maintains the granular structure and large magnetoresistance values. On the contrary, the samples turn into multilayers with continuous Co layers and small magnetoresistance with increasing Pt concentration. Small magnetoresistance values are also exhibited by the AgSi–Co samples. Post-deposition annealing of the Ag–Co and AgX–Co systems is examined and found to result in structural improvement of the films accompanied by monotonic GMR magnitude decrease.

Influence of Pt-doping on structural, magnetic and magnetotransport properties of granular Ag-Co multilayers

Abstract The effect of Pt doping on the Ag layers of granular Ag-Co multilayers is studied. Studies performed via X-ray diffractometry and transmission electron microscopy reveal a structural transition of the samples from granular to multilayer form dependent on Pt concentration. Magnetic hysteresis appearance and magnetoresistance ratio reduction also support the structural transition.