Study of optical properties of nano-cystalline semiconductors deposited from water based soution

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Dr. Kollár Ernő
Department of Electron Devices

The II-VI compound semiconductors, such as cadmium-sulphide nowadays are widely studied and used.

In this work I investigated optical properties of chemical bath deposited (CBD) cadmium-sulphide thin-films, primarily the effects of copper doping and thermal treatment. Our ultimate goal is to produce photoluminescent nanocrystalline materials. The research field is promising, some results in the literature show that these materials could compete with traditional phosphors.

The CdS thin-films were characterized using transmission, photoluminescence and photoconductivity measurements. With the help of these I also investigated the band gap, thickness and luminescent peaks of the samples.

The transmission measurements confirmed that by co-deposition (or doping) with copper the size of the nanocrystals becomes smaller due to the higher reaction rate. Optical band gap of undoped sample was 2.37 eV, the same quantity for copper co-deposited sample was 2.44 eV, which showed a decrease by 0.05 and 0.08 eV, respectively.

The photoluminescence measurements showed that the thermal treatment increases the luminescent intensity. In addition, it was found that with the increase of copper doping, the photoluminescence spectrum shifts towards longer wavelengths due to a copper-related luminescent center. The doping shifted the luminescent peak from less than 900 nm to 1030 nm.

In the thesis I describe the physical background necessary to understand the measurements, then I justify, why CdS and chemical bath deposition was chosen. Next I describe the measurements and present the results and conclusions. Finally, after the summary of the results, the unsolved questions are presented.


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