Nanostructuration of II-VI semiconductor materials for quantum communications technologies

Abstract

In recent years, the study of semiconductor nanocrystals with quantum properties has gained increasing interest, especially following the award of the 2023 Nobel Prize in Chemistry to the discovery and development of quantum dots. These materials have demonstrated great potential in optoelectronic applications and are nowadays proposed for quantum communication technologies. This work focuses on the synthesis of cadmium selenide (CdSe), which exhibits highly tunable optical properties depending on nanocrystal size because of the quantum confinement effect. The main objective of this study is to synthesise CdSe semiconductor nanocrystals using different methods: colloidal synthesis via the hot injection technique and solvothermal synthesis. In particular, is evaluated the potential of solvothermal synthesis as an alternative to conventional colloidal synthesis by studying aspects such as size control, morphology, optical properties, reproducibility, and its potential for large-scale application. This method has not been widely used for the synthesis of colloidal quantum dots, especially in CdSe-based systems. It is also intended to evaluate whether solvothermal synthesis can be a safer and simpler alternative from an experimental point of view compared to colloidal synthesis. To carry out this synthesis, CdSe samples were prepared by both colloidal and solvothermal methods under different reaction conditions. In the case of the solvothermal synthesis, two coordination cadmium precursors, based on stearic acid and myristic acid, were employed. The colloidal synthesis is based on the rapid injection of precursors into a hot medium to induce burst nucleation followed by controlled growth of the nanocrystals, which enables the production of highly monodisperse nanocrystals. On the other hand, solvothermal synthesis is carried out under high temperature and pressure conditions inside an autoclave, where similar nucleation and growth processes take place, yielding nanocrystals with good crystallinity using less stringent experimental conditions and a simpler and easily scalable procedure. Finally, the samples obtained were purified by precipitation and centrifugation processes and subsequently characterised using optical and structural techniques, including UV-Vis spectroscopy and photoluminescence, as well as high-resolution transmission electron microscopy (HRTEM) and X-ray diffraction. These techniques allow establishing a relationship between the synthesis conditions and the size, morphology, crystallinity, and optical properties of the CdSe nanocrystals, as well as evaluating the potential of the solvothermal synthesis as an alternative to the colloidal synthesis