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Electrical and structural characterization of Nb-Si thin alloy film

Published online by Cambridge University Press:  31 January 2011

F. Nava ,
P.A. Psaras ,
H. Takai ,
K.N. Tu ,
S. Valeri  and
O. Bisi
F. Nava
Affiliation:
IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598
P.A. Psaras
Affiliation:
IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598
H. Takai
Affiliation:
IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598
K.N. Tu
Affiliation:
IBM Thomas J. Watson Research Center, Yorktown Heights, New York 10598
S. Valeri
Affiliation:
Department of Physics, University of Modena, Modena, Italy
O. Bisi
Affiliation:
Department of Physics, University of Modena, Modena, Italy
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Abstract

The structural and electrical properties of a Nb-Si thin alloy film as a function of temperature have been studied by Auger electron spectrometry, Rutherford backscattering spectroscopy, transmission electron microscopies, and in situ electrical resistivity and Hall coefficient measurements. The NbSi2,8 films were deposited by double electron-gun coevaporation onto oxidized silicon. For electrical measurements samples of a van der Pauw pattern were made through metallic masks. In the as-deposited state the coevaporated alloy film was amorphous. Upon annealing a precipitous drop in resistivity near 270°C has been determined to be the amorphous to crystalline phase transformation. The kinetics of the transformation has been determined by isothermal heat treatment over the temperature range of 224°C to 252°C. An apparent activation energy of 1.90 eV has been measured. The nucleation and growth kinetics in the crystallization process show a change in the power of time dependence from 5.5 to 2.4. The microstructures of films at various states of annealing have been correlated to the resistivity change. The crystalline NbSi2 shows an anomalous metallic behavior. The resistivity (p) versus temperature curve has a large negative deviation from linearity (dfl) and it approaches a saturation value (psat) as temperature increases. The resistivity data are fitted by two empirical expressions put forth to explain the resistivity behavior in A15 superconductors at low and high temperatures. One is based on the idea that ideal resistivity must approach some limiting value in the regime where the mean free path becomes comparable to the interatomic spacing and the other is based on a selective electron-phonon assisted scattering. In spite of the wide temperature range of analysis, it is not possible to choose one of them due to the fact that the best fit in both cases is nearly the same. The Hall coefficient (RH) changes sign from negative above ∼250°K to positive below ∼ 250°K.

Type
Articles
Information
Journal of Materials Research , Volume 1 , Issue 2 , April 1986 , pp. 327 - 336
Copyright
Copyright © Materials Research Society 1986

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