Photoconductivity and Dc-Conductivity of super thin metallic layers

A. P. Boltaev, A. O. Pogosov, N. A. Penin, Fedor A. Pudonin ( pudonin-AT-sci-DOT-lebedev-DOT-ru.gif )
Solid State Physics Department, P.N.Lebedev Physical Institute of Russian Academy of Science, 117924, Moscow, Leninsky Pr.53, Russia.

Electron transport is studied in W, Fe, FeNi, Ti super thin (0.5-2.5 nm) metal and magnetic films, that was grown using RF-sputtering on sital and silicon substrates at room temperature.Grown films was protected by thin layer of Al2O3. AFM is used to analyze the surface topography of this structures. It was found that films with thickness d<1.5 nm are island shape films with typical sizes of the islands and distances between them ~ 2-5 nm depend on film thickness. The conductivity of these structures was measured in the range of 77-300 K. Current-Volt dependence for all structures was an ohmic type. It was found that electron flow is on activation character. The temperature dependence of the conductivity have shown that activation energy depends on film thickness. At light radiate of samples, the photoconductivity was observed, which disappeared at the film thickness d>1.5nm. The value of the photocurrent depends on film thickness and reaches its maximum at d ~ 0.9 nm. Reduction of the photoconductivity was observed at d < 0.9nm and d > 0.9 nm. Spectral dependence of the photoconductivity was studied at the range 0.6 - 2.0 mm. Reduction of the wavelength result to photoconductivity becomes 3-4 times greater. In particular, this photoconductivity shows great time of photocurrent's reaching stationary condition and its relaxation (~10-15 s.). Such great values of time were resulted from hopping conductivity on the localized states of the isolator layer separating the islands. So we study the electron transport in island shape films of various metals and found that electron flow is on activation character. Photoconductivity with great times of reaching of stationary condition was found in superthin films (d < 1.5nm). We present a model of current and photocurrent flow in such structures. This work was supported by National Russian program "Physics of solid state structures" (grant 97-1050) and RFBR grants.