Electrical properties of epitaxial tungsten films grown by laser ablation deposition

Abstract

An investigation was made of electrical properties of tungsten films of thickness in the range of 30–140 nm, grown by laser ablation deposition in ultrahigh vacuum on [1̄012] sapphire substrate. From the data on the size effect and the temperature dependence of the resistivity r, supported with reflection high energy electron diffraction measurements, we find that the films, deposited onto clean substrates kept at temperatures higher than 500 °C, grow epitaxially with high quality crystalline structure. The effective electron mean free path changes from 300 to 1400 nm while the residual resistance ratio RRR=r (295 K)/r (4.2 K) changes from 7 to 35. At low temperatures we find the temperature dependent part ρ(T)≊ATn, with A=1.56 mΩ cm K−n, n=3–3.4 for the temperatures T<20 K. From the fit of the data to the equations of the classical size effect theory it was found that the main source of electron scattering at helium temperatures is interface scattering with a specular coefficient q≊0.3 and the bulk electron mean free path l∞ (4.2 K)∼200 μm, which is up to 103 times larger than the film thickness.

Surface roughness dependence of the electrical resistivity of W(001) layers

“…This assumption is correct for various systems including, for example, Cu exposed to air 18,63 or coated with Ta 64 or Ti, 34 and also provides a method to determine the lower bound for k, since less diffuse scattering would lead to a larger value for p which, in turn, results in a larger value for k. 60 Correspondingly, we first fit the measured room temperature resistivity data with the FS model using a fixed p ¼ 0, but allow different effective mean free paths for the two sets of samples. The fitting provides values for the mean free path of 33.0 6 0.4 and 37.6 6 0.5 nm for annealed and asdeposited samples, respectively, with a tungsten bulk resistivity of q o ¼ 5.33 lX-cm at 295 K. These k values are close to the previously reported k ¼ 39.6 nm for W(001) with partial (p ¼ 0.3) specular scattering, 65 but are considerably larger than k ¼ 19.1 nm with p ¼ 0.11 for W(011) layers, 60 and k ¼ 15.5 or 19.1 nm from bulk density functional calculations. 44,60 The physical reasons for these differences are not completely clear, but may be attributed to anisotropy effects.…”

Electron mean free path of tungsten and the electrical resistivity of epitaxial (110) tungsten films

“…This low value of p indicates nearly fully diffuse scattering from the surfaces, as has also been seen for epitaxial Cu films. 33,34 The value of MSE for the fits is significantly lower than the MSE of 0.21 found in the work by Mikhailov et al where an EMFP of 39.6 nm was used for the fits 9 (see Table I). Furthermore, the fits to the resistivity data reported here did not require the use of an ad hoc parameter such as a dead layer, as was done by Mikhailov et al.…”

“…6 Similar to studies of Cu, studies of W (Refs. [7][8][9][10] have used the surface scattering model of Fuchs and Sondheimer 11,12 (FS) alone or in combination with the grain boundary scattering model of Mayadas and Shatzkes 13 (MS) in interpreting the results. The FS and MS models each incorporate a phenomenological parameter related to electron scattering at defects.…”

Pulsed laser deposition of tungsten and tungsten oxide thin films with tailored structure at the nano- and mesoscale

“…Among these, tungsten and tungsten oxide films have been investigated for applications in the fields of microelectronics, sensing and catalysis. For instance, tungsten thin films have been studied for the development of electrical contacts [3,4], while tungsten oxide films present gas sensing (via molecule adsorption and subsequent surface conductivity variation), electrochromic [5][6][7] and catalytic properties [8]. For these applications the increase of the specific effective surface and the comprehension of the transport properties is of great importance.…”

“…Transition metal and metal oxide films are interesting materials in view of the possibility of growing functional coatings with tailored properties [1][2][3][4][5][6][7][8]. Among these, tungsten and tungsten oxide films have been investigated for applications in the fields of microelectronics, sensing and catalysis.…”