Untersuchung des reaktiven Sputterprozesses zur Herstellung von ...

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Untersuchung des reaktiven Sputterprozesses zur Herstellung von ...

ii Kurzfassung

Investigation of the reactive sputtering process for preparation of

aluminum doped zinc oxide films for silicon thin film solar cells

This thesis addresses the development of aluminum doped zinc oxide (ZnO:Al) films by

reactive sputter deposition. The study focuses on the relation between deposition conditions and

the resulting electrical, optical and structural film properties. The structure of the ZnO:Al films

strongly affects the surface morphology obtained after wet chemical etching. The technological

goal was the design of ZnO:Al films with optimized surface texture and thus light scattering

properties for the application as front contact in amorphous (a-Si:H) and microcrystalline (µc-

Si:H) based thin film solar cells.

The comparatively low absorption coefficient of silicon in the long wavelength range of the

sun spectrum necessitates additional mechanisms to enhance light absorption within the silicon

layers. This can be realized by a combination of rough, light scattering front contacts and

highly-reflective rear contacts. Initially smooth, sputter deposited ZnO:Al films can be roughened

by post-deposition wet-chemical etching. In the ideal case, these rough layers introduce almost

completely diffuse transmission, and back reflector and front contact guide the light through the

silicon layers until it is totally absorbed (ideal light trapping).

The ZnO:Al films were prepared by reactive mid-frequency (MF) sputtering from metallic

Zn:Al targets in a vertical in-line deposition system. Initially, technological aspects like stabilization

of the working point and the influence of substrate movement required for dynamic

deposition were studied. Doping concentration and deposition conditions were varied to optimize

the optical and electrical ZnO:Al properties, leading to resistivities ρ

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