Electrical transport properties in Co-silicides formed by thin-film reactions

Abstract

Four different Co-silicide compounds were obtained by solid-state reaction at 800 °C in thin bilayers of amorphous silicon and cobalt evaporated on SiO2 substrates. Rutherford backscattering spectroscopy (2 MeV 4He+), x-ray diffraction, and Auger electron spectroscopy were used to obtain information about the chemical and crystallographic characteristics of the samples. Results indicate that in each sample only one of the following phases is present: CoSi2, CoSi, Co2Si, and Co4Si, the latter identified on the basis of the stoichiometric ratio only. Electrical resistivity and Hall effect measurements on van der Pauw structures were carried out as a function of the temperature in the intervals: 10–1000 and 10–300 K, respectively. At room temperature the resistivity ranges from the value 19 μΩ cm for CoSi2 to the value 142 μΩ cm for CoSi. There are some analogies with the case of a classical metal, but remarkable differences are also detectable in the resistivity versus temperature behavior and in the order of magnitude of the resistivity and of the Hall coefficient. In particular, at T>300 K the resistivity of the CoSi2 samples linearly depends on temperature and is well fitted by the classical Bloch–Grüneisen expression. The other silicides show, in the same temperature range, a deviation from linearity (d2ρ/dT2<0), while a quasi saturation of the resistivity can be extrapolated at higher temperatures. This saturation phenomenon can be described by the parallel of an ideal conductivity and of a saturation conductivity, and associated with the electron mean free path approaching interatomic distances. A similar model already has been put forth to describe the saturation of the resistivity in systems, such as A-15 superconducting compounds, characterized by a high value of the room-temperature resistivity. The transport parameters, deduced in a free electron framework from the resistivity curves of the Co silicides, show values which are consistent with the proposed model. Hall coefficient versus temperature behavior indicates that between 10 and 300 K a multicarrier effect is present. Conduction is predominantly n type in CoSi and p type in the other silicides.

Optical properties of Co silicides: Experiment and density functional theory

“…7͒, which is similar to that observed by van der Marel et al, 2 Aprilesi et al, 26 and Nava et al 27 Although the ͑T͒ curve shows a typical metallic behavior, there are some differences among them: ͑T͒ dependence obtained by van der Marel et al 2 is almost linear in the 70-300 K temperature range, while that of Aprilesi et al 26 ͑and this study, see Fig. 7͒, which is similar to that observed by van der Marel et al, 2 Aprilesi et al, 26 and Nava et al 27 Although the ͑T͒ curve shows a typical metallic behavior, there are some differences among them: ͑T͒ dependence obtained by van der Marel et al 2 is almost linear in the 70-300 K temperature range, while that of Aprilesi et al 26 ͑and this study, see Fig.…”

Atomic size effects studied by transport in single silicide nanowires

“…Similar values were reported for other silicides (e.g., CoSi 2 [64][65][66] or NiSi [67]). Qualitatively, this already explains why the resistivity measured in our case is so sensitive to the height rather than to the width of the wires.…”

B20 Weyl Semimetal CoSi Film Fabricated by Flash-Lamp Annealing

“…It is known that thin films grown on substrates of technological relevance are appreciated for many practical applications. − However, based on our current knowledge, there are only few studies about Weyl semimetal B20-CoSi films. In early reports about the growth of Co-silicide thin films, it was found that Co 2 Si and CoSi 2 always coexist with B20-CoSi. , Therefore, separating the Co-Si compounds is challenging but is necessary for understanding the topological properties of CoSi films. Tang et al have first prepared polycrystalline CoSi films on Al 2 O 3 by magnetron sputtering.…”

“…In early reports about the growth of Co-silicide thin films, it was found that Co 2 Si and CoSi 2 always coexist with B20-CoSi. 22 , 23 Therefore, separating the Co-Si compounds is challenging but is necessary for understanding the topological properties of CoSi films. Tang et al have first prepared polycrystalline CoSi films on Al 2 O 3 by magnetron sputtering.…”