Anisotropy in surface resistivity due to electron-phonon scattering in aluminium

Abstract

The electrical resistivi@ p has teen measured at temperatures from 1.5 to 75 K for two series of foils with ( l l l } and (110) surfaces on zone-refined Al. under the same current direction of (112). It is found that p is larger on the { l l l ) foil than the (110) one at 15-60 K and their difference peaks at around 35 K. The analysis of the data with Fuchdondheimer theory gives the following results. (i) The phonon-limited part of the bulk-electron mean free path, lb(T), is larger along about (111) (I;"(T)) than the orientations around (110) (l~l'(T)). and agrees with the value from thc electron-phonon scattering time calculated by h u n g et 01 at 20 K. (ii) lLLL(T) varies as T-3.0, but 1iIo(T) varies as T-3.5 at 10-20 K this is comistent withMeador and Lawrence's theoretical prediction. me surface resistivity h of the single crystals is about half of that of the polycrystal of pure Al. It is concluded that the enhancement of , & due to anisotropy in lb(T) is the main cause of the discrepancies between the measured and predicted h in polycrystals.than that estimated from FS theory, as reviewed by Bass (1972). Sambles and Elson (1980) have explained this discrepancy, using Soffer's (1967) surfacereflection parameter, which depends on the electron incidence angle (Soffer's theory). This explanation, however, was later doubted by themselves, because these theories are based on the isotropic relaxation time and AI has a rather complicated Fermi surface (Sambles and Mundy 1983).Recently, the present author has found that the nature of bulk scattering has a great effect on ps. Instead of temperature, we have varied the concentration of Ag in diiute Al-Ag polycrystalline foils at 4.2 K to vary the bulk mean free path db. ps of the solid solution of AI-Ag at 4.2 K bas been shown to be smaller than that of pure Al at tens of kelvin, in good agreement with FS theory (Nakamichi and Kino 1988). In addition, in the more concentrated AI-Ag alloys with Guinier-Preston (GP) zones, the ps at 4.2 K becomes four to five times larger than that of the AI-Ag solid solution (Nakamichi 1989). These results are consistent with the theoretical prediction of Bate et al (1963) that the anisotropy in mean free path enhances ps in polycrystals, because the GP zone has a strongly anisotropic scattering in contrast to the fairly isotropic scattering of the A1-Ag solid solution. These results suggest that the discrepancy between measured and calculated p. at low temperatures arises from the anisotropy in electron-phonon scattering (Nakamichi and Kino 1988).