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The Luminescent Inhomogeneity and the Distribution of Zinc Vacancy-Related Acceptor-Like Defects in N-Doped ZnO Microrods

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ABSTRACT

Vertically aligned N-doped ZnO microrods with a hexagonal symmetry were fabricated via the chemical vapor transport with abundant N2O as both O and N precursors. We have demonstrated the suppression of the zinc interstitial-related shallow donor defects and have identified the zinc vacancy-related shallow and deep acceptor states by temperature variable photoluminescence in O-rich growth environment. Through spatially resolved cathodoluminescence spectra, we found the luminescent inhomogeneity in the sample with a core-shell structure. The deep acceptor-isolated VZn and the shallow acceptor VZn-related complex or clusters mainly distribute in the shell region.

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The schematic model of one N-doped ZnO MR with core-shell-structured luminescent inhomogeneity
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Fig8: The schematic model of one N-doped ZnO MR with core-shell-structured luminescent inhomogeneity

Mentions: The inhomogeneous distribution of the acceptor-like defects can be unified to the difference between surface and bulk. It is a well-known fact that surface defects of metal oxides function as adsorption sites [44]. The adsorption of a gas molecule, such as O2 or H2O, on the surface of ZnO will trap the free electrons to form negative O2− or OH− ions. Therefore, the adsorbates acting as acceptors deplete the surface electron states, leaving behind positively charged native defects or dopants near the surface, resulting in the space charge region and band bending of the surface [45, 46]. Due to larger surface-to-volume ratio, such a surface effect is more significant on ZnO nanostructures, compared with bulk materials. A layer that is depleted of mobile electrons is then created at the surface of the ZnO MR, the width of which is up to more than 100 nm [47]. Moreover, it has been reported that the VZn− centers only exist in the depletion layer [48], which could compensate for an intrinsic charge imbalance. In addition to the results reported by Fabbri et al. [10], all the above discussions suggest that both the VZn-related complex shallow acceptors and the isolated VZn deep acceptors are mainly located near the surface region of the MRs. The intensified FX in bulk area and the disappearance of the peak at the surface area indicate that the crystalline quality is relatively better in bulk and relatively worse at surface. Possibly, for this very reason, more acceptor-like isolated and complex defects can form at the MR surface region. The “core-shell” luminescent structure of the N-doped ZnO MRs has been schematically drawn in Fig. 8. With further design and optimization of the experiment conditions, it might be possible to achieve a co-axial p–n junction which can be potentially applied to co-axial light-emitting devices.Fig. 8


The Luminescent Inhomogeneity and the Distribution of Zinc Vacancy-Related Acceptor-Like Defects in N-Doped ZnO Microrods
The schematic model of one N-doped ZnO MR with core-shell-structured luminescent inhomogeneity
© Copyright Policy - OpenAccess
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5120051&req=5

Fig8: The schematic model of one N-doped ZnO MR with core-shell-structured luminescent inhomogeneity
Mentions: The inhomogeneous distribution of the acceptor-like defects can be unified to the difference between surface and bulk. It is a well-known fact that surface defects of metal oxides function as adsorption sites [44]. The adsorption of a gas molecule, such as O2 or H2O, on the surface of ZnO will trap the free electrons to form negative O2− or OH− ions. Therefore, the adsorbates acting as acceptors deplete the surface electron states, leaving behind positively charged native defects or dopants near the surface, resulting in the space charge region and band bending of the surface [45, 46]. Due to larger surface-to-volume ratio, such a surface effect is more significant on ZnO nanostructures, compared with bulk materials. A layer that is depleted of mobile electrons is then created at the surface of the ZnO MR, the width of which is up to more than 100 nm [47]. Moreover, it has been reported that the VZn− centers only exist in the depletion layer [48], which could compensate for an intrinsic charge imbalance. In addition to the results reported by Fabbri et al. [10], all the above discussions suggest that both the VZn-related complex shallow acceptors and the isolated VZn deep acceptors are mainly located near the surface region of the MRs. The intensified FX in bulk area and the disappearance of the peak at the surface area indicate that the crystalline quality is relatively better in bulk and relatively worse at surface. Possibly, for this very reason, more acceptor-like isolated and complex defects can form at the MR surface region. The “core-shell” luminescent structure of the N-doped ZnO MRs has been schematically drawn in Fig. 8. With further design and optimization of the experiment conditions, it might be possible to achieve a co-axial p–n junction which can be potentially applied to co-axial light-emitting devices.Fig. 8

View Article: PubMed Central - PubMed

ABSTRACT

Vertically aligned N-doped ZnO microrods with a hexagonal symmetry were fabricated via the chemical vapor transport with abundant N2O as both O and N precursors. We have demonstrated the suppression of the zinc interstitial-related shallow donor defects and have identified the zinc vacancy-related shallow and deep acceptor states by temperature variable photoluminescence in O-rich growth environment. Through spatially resolved cathodoluminescence spectra, we found the luminescent inhomogeneity in the sample with a core-shell structure. The deep acceptor-isolated VZn and the shallow acceptor VZn-related complex or clusters mainly distribute in the shell region.

No MeSH data available.