Photoluminescence properties of ZnO nanoneedles grown by metal organic chemical vapor deposition

Abstract

The authors report on growth of ZnO nanoneedles (NNs) by metal organic chemical vapor deposition (MOCVD). Photoluminescence spectra of the NNs at 20 K are dominated by a surface excitonic (SX) emission at 3.367 eV. Temperature-dependent PL reveals the activation energies for the quenching of SX (∼11.2 meV) and donor bound excition (∼21 meV) are close to their localization energies. From 20 K to room temperature, no obvious green emission is observed. These characteristics demonstrate that the surface of NNs grown by MOCVD are not necessarily subjected to nonradiative or deep-level defects on the surface of ZnO nanorods grown by vapor transport method. Furthermore, using three different expressions, we fit the data of temperature dependent A free exciton energy (FXA) transition energy and the results are described and compared. The Debye and Einstein temperatures are found to be 660 and 238 K, respectively. The dependence of the full width at half maximum of the FXA peak as a function of temperature is investigated. The broadening of FXA band is mainly attributed to the scattering by the acoustic phonons in the NNs.