A first-principles study of II–VI (II = Zn; VI = O, S, Se, Te) semiconductor nanostructures

Abstract

We present a systematic investigation of the structural, electronic and optical properties of wurtzite-like ZnX (X = O, S, Se, Te) nanostructures at the DFT/TDDFT level of theory. To provide a direct comparison with the experiment, realistic 1.0–1.5 nm quantum dots have been built up from the bulk. Low-lying computed excitation energies agree well with the available experimental data. The broad excitation profiles and narrow emission spectra typical of semiconductor quantum dots could be explained by the fact that the LUMO is the state accepting the electron of the low-lying TDDFT excitations calculated. Calculated binding energies for the Zn 3d shell have been found to be 0.5 eV lower than those of the corresponding bulk materials. Anion vacancies can explain the visible light emission of ZnX by introducing a trap state into the bandgap of the nanostructures, in agreement with previous theoretical and experimental works on ZnO. Calculations on rod- and sheet-like prototype clusters point to a significant quantum confinement effect on the optoelectronic properties of Zn-based nanomaterials.