Photoconductivity and Dc-Conductivity of super thin metallic layers
A. P. Boltaev, A. O. Pogosov, N. A. Penin,
Fedor A. Pudonin (

)
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.