The particular properties of nanomaterials can be an opportunity for developing a new low cost and a high efficient generation of solar cells. Semiconducting nanocrystals can be used as quantum dots to realize band gap engineering by varying the nanocrystals size. The subject of research is to synthesize a composite material based on Ge nanocrystals embedded in various matrices and perform characterizations. A nanocluster source, under vacuum sputtering setup, was used to synthesize Ge nanoparticles. The vapor phase condensation leads to the formation of well crystallized nanoparticles, for a deposition performed at room temperature. This synthesis method allows a good control of the nanocrystals size and the nanocrystals quantity inserted in the material. Optical properties of Ge nanocrystals embedded in insulating and semiconducting matrices were studied. We have demonstrated the quantum dot behavior of Ge nanocrystals. We have also shown the ability to modulate the nanocrystals band gap from 0.85 to 1.55 eV by varying the nanocrystals size and the potential barriers. Optoelectronical characterizations were performed to estimate the ability to extract and collect the carriers photogenerated in the Ge nanocrystals by light absorption. Ge nanocrystals in ZnO:Al matrix forms type-II quantum dots. This heterostructure is very interesting because it allows the spatial separation of the carriers while keeping the quantum confinement properties. We have brought out a photovoltaic effect with the structure p+-Si wafer / Ge nanocrystals / ZnO:Al matrix. We have also demonstrated that the carrier generation only occurs in the Ge nanocrystals.
