Advanced materials for highly efficient energy processes: study of their optical properties

This project deals with optical processes in materials of great current interest due to their potential applications in new generation optoelectronic devices. The study of optical processes yields rellevant information about the specific characteristics of the new functional materials and allows a characterization of their properties at macroscopic and submicrometric scale. The work will focus on the study by means of Raman spectroscopy, photoluminescence (PL) and cathodoluminescence (CL) of the optical properties in three groups of materials which are arising a great deal of interest: i) nanostructured group-III nitrides, which have interesting applications in photovoltaics and light emitters in the visible-ultraviolet range; ii) semiconducting oxides with photovoltaic applications, both thin films of transparent conducting group-III oxides and group-II oxide alloys and nanostructures; iii) transition metal chalcogenides, which form bidimensional crystals and have emerged as alternatives to graphene with interesting specific characteristics. The studies on these materials will be complemented by the analysis of their optical properties under hydrostatic pressure. Within the nanostructured materials of group i), the study of the vibrational modes of InGaN nanowires (NW) and their dependence on composition will be undertaken. The study of NWs under hydrostatic pressure will provide a more accurate determination of pressure coefficients in relaxed InGaN crystals, free from the substantial strain effects due to substrate mismatch affecting the epitaxial layers. The effect of free charge will be studied in Si-doped GaN micro wires, and the free-electron density will be determined by means of micro- Raman optical measurements. Within the group ii), the study of alfa-Ga2O3 and its alloying with In2O3, and subsequently with Al2O3, will be addressed. Raman spectroscopy will yield information about the sample quality which will be complemented with CL studies on their emission properties and homogeneity at the submicrometer scale. On the other hand, the transparent oxide alloy CdZnO will be studied as a window in CdZnO/CdTe quantum dots and wells for photovoltaic applications. These nanostructures will be thoroughly characterized by means of the analysis of Raman, PL and CL measurements. ZnO core-shell nanowires with an extra thin absorbing II-VI layer for photovoltaic applications will also be studied. Regarding the group iii), the project will focus on obtaining detailed information of MoS2 layers used in FET fabrication and its correlation with the characteristics of the devices. By means of CL analysis, the homogeneity of the layers and the modification of the optical properties in chemically treated layers will be studied.

Researchers

• Juan Jiménez López (UVA)