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Ge/Si core/shell quantum dots (QDs) recently received extensive attention due to their specific properties induced by the confinement effects of the core and shell structure. They have a type II confinement resulting in spatially separated charge carriers, the electronic structure strongly dependent on the core and shell size. Herein, the experimental realization of Ge/Si core/shell QDs with strongly tunable optical properties is demonstrated. QDs embedded in an amorphous alumina glass matrix are produced by simple magnetron sputtering deposition. In addition, they are regularly arranged within the matrix due to their self-assembled growth regime. QDs with different Ge core and Si shell sizes are made. These core/shell structures have a significantly stronger absorption compared to pure Ge QDs and a highly tunable absorption peak dependent on the size of the core and shell. The optical properties are in agreement with recent theoretical predictions showing the dramatic influence of the shell size on optical gap, resulting in 0.7 eV blue shift for only 0.4 nm decrease at the shell thickness. Therefore, these materials are very promising for light-harvesting applications.

The preparation of non-oxidized Ge quantum dot (QD) lattices embedded in Al 2 O 3 , Si 3 N 4 , SiC matrices by self-assembled growth was studied. The materials were produced by magnetron sputtering deposition, using different substrate temperatures. The deposition regimes leading to the self-assembled growth type and the formation of three-dimensionally ordered Ge QD lattices in different matrices were investigated and determined. The oxidation of the Ge QDs in different matrices was monitored and the best conditions for the production of non-oxidized Ge QDs were found. The optical properties of the Ge QD lattices in different matrices show a strong dependence on the Ge oxidation and the matrix type.

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A method to enhance the optoelectronic properties of thin films containing three-dimensional ordered germanium quantum dots (QDs) coated with metal shell (Al, Ta, and Ti) in alumina matrix is presented. The conditions for the achievement of self-assembled growth of the metal-coated Ge QDs by magnetron sputtering deposition are explored. The influence of the metal shell on the structural, optical, and optoelectronic properties is found to be radical and desirable. First, it reduces Ge oxidation. Second, it enhances overall absorption by an order of magnitude. Third, it enables manipulation of the absorption curve shape in two ways. The Ge absorption peak, useful for photoelectric conversion, can be tuned significantly via control of the Ge energy gap because of the quantum confinement effect. On the other hand, infrared absorption can be controlled by the amount of metal because the geometry of the system can enhance absorption in the core by excitation of plasmon resonances in the shell. The mentioned effects result in a high increase of the photocurrent and quantum efficiency of core−shell nanoparticles compared to simple Ge particles. The experiments are supported by theoretical predictions, showing that the intensity of the incident radiation is strongly amplified in the region around the metal−semiconductor interface upon the excitation of plasmon resonances, hence increasing the probability of photon absorption and, thus, of charge carrier generation in the photo-active material. Therefore, the presented materials are very promising for photoelectric devices.