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Ge quantum dot lattices in alumina prepared by nitrogen assisted deposition: structure and photoelectric conversion

Thin films comprising of three dimensional germanium (Ge) quantum dot lattices formed by nitrogen (N) assisted magnetron sputtering deposition in alumina (Al2O3) matrix have been studied for light harvesting purposes. In order to expand the application of this material it is necessary to reduce germanium oxidation and to achieve stabilization of germanium/alumina interface. [1, 2] Effects of tuning the nitrogen concentration, substrate temperature and Ge sputtering power during the films preparation are monitored. It is shown that the N presence not only reduces germanium oxidation during annealing but also affects the size and arrangement of germanium quantum dots. Deposition temperature and Ge sputtering power affect Ge quantum dot size, separation and the regularity of their positions. Consequently, optical and electrical properties of the films, especially their photo- current, strongly depend on the deposition conditions. Additionally, the film deposited at 500 °C shows the multiple exciton generation and significant photo response, so it could be used as a sensitive layer for photodetectors or photovoltaic light harvesting devices. We have shown how to manipulate the photogeneration properties and its dependence on the light energy by materials structure, especially on the Ge QD size and its internal structure. The above mentioned effects and the material itself could be very useful in light harvesting and production of heavy –metal free high-efficient solar cells.

germanium QDs ; multilayer deposition ; multiple exciton generation

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