Optical properties of Si and Ge nanocrystals: Parameter‐free calculations

Abstract

AbstractThe cover picture of the current issue refers to the Edi‐tor's Choice article of Ramos et al. [1]. The paper gives an overview of the electronic and optical properties of silicon and germanium nanocrystals determined by state‐of‐the‐art ab initio methods. Nanocrystals have promising applications in opto‐electronic devices, since they can be used to confine electrons and holes and facilitate radiative recombination. Since meas‐urements for single nanoparticles are difficult to make, ab initio theoretical investigations become important to understand the mechanisms of luminescence.The cover picture shows nanocrystals of four sizes with tetrahedral coordination whose dangling bonds at the surface are passivated with hydrogen. As often observed in experiments, the nanocrystals are not perfectly spherical, but contain facets. Apart from the size of the nanocrystals, which determines the quantum confinement, the way their dangling bonds are passivated is relevant for their electronic and optical properties. For instance, the passivation with hydroxyls reduces the quantum confine‐ment. On the other hand, the oxidation of the silicon nanocrys‐tals increases the quantum confinement and reduces the effect of single surface terminations on the gap. Due to the oscillator strengths of the lowest‐energy optical transitions, Ge nanocrys‐tals are in principle more suitable for opto‐electronic applica‐tions than Si nanocrystals.The first author, Luis E. Ramos, is a postdoc at the Institute of Solid‐State Physics and Optics (IFTO), Friedrich‐Schiller University Jena, Germany. He investigates electronic and optical properties of semiconductor nanocrystallites and is a member of the European Network of Excellence NANO‐QUANTA and of the European Theoretical Spectroscopy Facility (ETSF).