Role of structural defects in electron transport properties of copper films

Abstract

Kinetics of annealing of the electrical resistivity (ρ), Hall coefficient R_H, mobility μ, and thermoelectric power TEP of thin (160-5000 Å) copper films deposited at temperatures ranging from 80 to 600 K have been studied. The activation energy for the associated recovery process has been obtained from the observed isothermal and isochronal changes in the resistance of the films. This energy increases from a value of 0.7 eV at 2000 Å to 1.4 eV at 180 Å for room-temperature-deposited Cu films. Changes in ρ, R_H, and μ on annealing are found to decrease with film thickness and deposition and annealing temperatures. On the other hand, changes in TEP due to annealing increase with film thickness up to 3000 Å; the rate of change depends sensitively on deposition temperature. With decreasing temperature of deposition, the reduction in TEP occurs at successively higher annealing temperature. Annealing does not affect the temperature dependence of R_H and TEP. These results, together with the information on the microstructure of the films and the known scattering behavior of structural defects in the bulk, lead us to conclude that (1) the reduction in ρ, R_H, and μ on annealing is due to the annihilation of vacancies; (2) the corresponding changes in TEP are due to the decrease in the concentration of vacancies as well as the density of dislocations. Quantitative effects of vacancies and dislocations on R_H and TEP have been deduced from the observed data. The enormously large contributions of the defects may be understood qualitatively in terms of the variations in the density of holelike states and/or the energy dependence of conductivity (at the Fermi surface), caused by changes in the extent and/or degree of curvature of the necks at the Fermi surface.