Indium tin oxide (InSnO₂, ITO) is known as a transparent oxide with n-type electrical conductivity. However, the as grown ITO layers have high resistivity and the transparency is also very limited. In this work ITO layers were deposited by evaporation and then underwent a post-growth annealing. Annealing leads to low electrical resistivity and to an enhanced transparency. Annealed samples show n-type conductivity.

Since sensor chips used in optical waveguide lightmode spectroscopy (OWLS) can be coated with various solid layers in order to achieve either simply improved or more selective sensor sensitivity, ITO coating layers are envisaged for measurements where the layer conductivity plays an important role. One of such cases is when the optical sensitivity can be combined with specific advantages of the electrochemical processes.

ITO layers of typically 10 nm thickness were deposited onto OWLS sensor chips and on SiTiO covered glass substrates. The basic measurement after the annealing was the conductivity determination. On sensor chips also the angle dependent photocurrent spectra were evaluated. This allows the selection of the chips.

The electrical conductivity was estimated first by two point direct resistance measurements, then by van der Pauw configuration and by collinear four point probe method. W needles, Sn containing mechanical contacts, In, Ga and In+Ga wetting contacts, and some alloyed contacts (In, Au, Sn) were used. All types of contacts proved to be applicable. Also the repetitivity of the technological processes was controlled partly by electrical measurements.

The storage time dependent stability and light sensitivity were studied. It is demonstrated that the resistance decreases due to the illumination, but in a very small extent. The decrease depends on the wavelength and the process is very slow (tens of minutes, up to hours). The recovery is also slow and also some drift in resistance is observed under continuous repetitive measurements.

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2. Some Optical Effects on the Electrical Conductivity of ITO Nanoscale Layers
3. Combination of the Optical Waveguide Lightmode Spectroscopy Method with Electrochemical Measurements
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