Excitons in germanium nanowires: Quantum confinement, orientation, and anisotropy effects within a first-principles approach

Within a first-principles framework we show how many-body effects crucially modify the electronic and optical properties of free-standing Germanium nanowires. The electron-hole binding energy and probability distribution are found to depend on both wire size and orientation. Moreover, we observe an almost complete compensation of self-energy and excitonic effects for some of the analyzed quantum wires, which we explain as being due to their clusterlike atomic structure.