Exceptionally Long Exciton Photoluminescence Lifetime in ZnO Tetrapods

Abstract

The fabrication of ZnO tetrapods of an exceptional optical quality, based on a photoluminescence (PL) lifetime in the range of tens of nanoseconds and the absence of defect emission, is found to be possible in a very narrow temperature range only. A reduction in the PL lifetime and an increase in the defect emission are observed for both higher and lower growth temperatures. The obtained PL lifetime for the optimal growth temperature is an order of magnitude higher than the best results achieved in epilayers and single crystals. Temperature dependence of the PL lifetime of high-quality tetrapod samples indicates that the dominant recombination processes are radiative.

Long lifetime of free excitons in ZnO tetrapod structures

“…In sharp contrast, the PL decay in bulk ZnO is much faster and is described by a single decay time of 0.5 ns. This may indicate superior optical quality of the investigated tetrapod structures as the decay time of the slow PL component is comparable to the largest values of 14 and 27 ns reported so far in the literature for bulk 1 and nanostructured ZnO, 10 respectively.…”

“…The desire for efficient light emitters has motivated considerable interest in exciton dynamics [1][2][3][4][5][6][7][8][9][10] as it provides information both on efficiency of radiative recombination, determined by oscillator strength of the corresponding optical transitions, and also on material quality reflected by contributions of nonradiative recombination in lifetimes of photogenerated carriers. The decay time of excitonic photoluminescence ͑PL͒ reaches several nanoseconds at RT in high quality ZnO single crystals 1,5 but is substantially shorter ͑ϳhundreds of picoseconds͒ in ZnO nanostructures.…”

ZnO Tetrapods: Synthesis and Applications in Solar Cells

“…These novel nanostructures indicate that ZnO contains probably the richest family of nanostructures among all materials, in both structure and properties, as well as providing valuable models for understanding crystal-growth mechanisms at nanosize, and exhibiting high potential for fabricating novel nanoelectronics and optical devices with enhanced performance [6]. Among the various morphologies of ZnO nanostructures, ZnO tetrapods have recently attracted extensive attention due to their unique shape and structure, excellent optical properties and significantly lower density of native defects when compared to other morphologies [7]. A ZnO tetrapod consists of a ZnO core from which four arms extend to the surrounding space at the same extent, which endows them with the ability to assemble a good network with desired the porosity and mechanical strength by connecting arms with each other.…”

High Quantum Efficiency of Band-Edge Emission from ZnO Nanowires

“…9 However, above a certain temperature growth conditions become unfavorable and nanostructure material quality suffers. 17 Therefore, determination of the optimal growth temperature is necessary for high material-quality nanostructures with functional geometries. In Figures 4a and 4b the PL spectra and EQE values of ZnO 7 nanowires are plotted vs nanowire growth temperature, respectively.…”