First-principles study of the electronic and optical properties of ZnO and ZnS wurtzite nanoclusters

Zinc oxide (ZnO) and zinc sulphide (ZnS) nanostructures have emerged in recent years as promising candidates in the development of nanoscale electronic and photonic devices. Theoretical studies on the properties of nanosized wurtzite ZnO and ZnS are rather scarce and their electronic and optical properties are largely unknown to date. As a part of a more general theoretical effort aimed at the multiscale modelling of nanohybrids for photovoltaics, we computed size-dependent electronic and optical properties of ZnO and ZnS nanoclusters with wurtzite structure, using Density Functional Theory (DFT), Time-Dependent DFT (TDDFT) and Many Body Perturbation Theory methods. We discuss general trends for binding energy, ionization energy and electron affinity, fundamental electronic gap, excitonic effects, and optical absorption spectra as a function of cluster size and wire diameter. We found good agreement with the experimental data available for the two materials. A comparison between TD-DFT and Many Body theories shows for both materials a general good agreement for the optical absorption spectra of this class of nanocrystals.