We investigated the production conditions and optoelectrical properties of thin film material consisting of regularly ordered core/shell Ge/Al and Ge/Si3N4/Al quantum dots (QDs) in an alumina matrix. The materials were produced by self–assembled growth achieved by means of multilayer magnetron sputtering deposition. We demonstrated the successful fabrication of well-ordered 3D lattices of Ge/Al and Ge/Si3N4/Al core/shell quantum dots with a body-centred tetragonal arrangement within the Al2O3 matrix. The addition of shells to the Ge core enables a strong tuning of the optical and electrical properties of the material. An Al shell induces a bandgap shift toward smaller energies, and, in addition, it prevents Ge oxidation. The addition of a thin Si3N4 shell induces huge changes in the material spectral response, i.e., in the number of extracted excitons produced by a single photon. It increases both the absolute value and the width of the spectral response. For the best sample, we achieved an enhancement of over 250% of the produced number of excitons in the measured energy range. The observed changes are, as it seems, the consequence of the large tensile strain in Ge QDs which is induced by the Si3N4 shell addition and which is measured to be about 3% for the most strained QDs. The tensile strain causes activation of the direct bandgap of germanium, which has a very strong effect on the spectral response of the material.

Thin films containing 3D-ordered semiconductor quantum wires offer a great tool to improve the properties of photosensitive devices. In the present work, we investigate the photo-generated current in thin films consisting of an interconnected 3D-ordered network of Ge quantum wires in an alumina matrix. The films are prepared using nitrogen-assisted magnetron sputtering co-deposition of Ge and Al2O3. We demonstrate a strong photocurrent generation in the films, much stronger than in similar films containing Ge quantum dots. The enhanced photocurrent generation is the consequence of the multiple exciton generation and the films’ specific structure that allows for efficient carrier transport. Thin film with the largest nitrogen content showed enhanced performance compared to other thin films with 1.6 excitons created after absorption of a single photon at an energy nearly equal to the double bandgap value. The bandgap value depends on the geometrical properties of the quantum wires, and it is close to the maximum of the solar irradiance in this case. In addition, we show that the multiple exciton generation is the most pronounced at the photon energy values equal to multiple values of the thin film bandgap.

The properties of semiconductor materials can be strongly affected by the addition of metallic nanoparticles. Here we investigate the properties of SiC+Au and Si3N4+Au thin films prepared by magnetron sputtering deposition followed by thermal annealing. The influence of gold addition on the optical and electrical properties is explored. We show the formation of self-assembled Au nanoparticles in SiC and Si3N4, with the size and arrangement properties determined by the deposition and annealing conditions. Both SiC- and Si3N4-based films show an increase in the overall absorption with increasing Au content, and its decrease with increasing annealing temperature. All films show the presence of surface plasmon resonance, whose peaks shift toward larger wavelengths with increasing Au nanoparticle size. The resistivity significantly drops with the Au content increase for both types of matrices, although the resistivity of Si3N4-based films is much higher. The incorporated quantity of Au in the host matrix was chosen in such a way to demonstrate that a huge range of optical and electrical characteristics is achievable. The materials are very interesting for application in opto-electronic devices.

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