Tailoring the charge carrier dynamics in ZnO nanowires: The role of surface hole/electron traps

Mingjie Li, Guichuan Xing, Lloyd Foong Nien Ah Qune, Guozhong Xing, Tom Wu, Cheng Hon Alfred Huan, Xinhai Zhang, Tze Chien Sum

Research output: Journal article publicationJournal articleAcademic researchpeer-review

48 Citations (Scopus)

Abstract

Post-fabrication thermal-annealed ZnO nanowires (NWs) in an oxidizing (or a reducing) ambient were investigated using transient photoluminescence and X-ray photoelectron spectroscopy. Our findings reveal an ultrafast hole-transfer process to the surface adsorbed oxygen species (e.g., O 2 -) occurring within a few hundred picoseconds (ps) in the air-annealed samples; and an ultrafast electron-transfer process to charged oxygen vacancies (i.e., V O 2+) occurring within tens of ps in the H 2-annealed samples. Contrary to the common perception that the band edge emission (BE) dynamics are strongly influenced by the carrier trapping to the green emission related defect states (i.e., V Zn), these above processes compete effectively with the ZnO BE. Hole trapping by ionized V Zn, which occurs in an ultrashort sub-ps-to-ps timescale (and hence limits its effective hole capture radius), however, has less influence on the BE dynamics. Importantly, our findings shed new light on the photoinduced charge transfer processes that underpins the novel properties of enhanced photocatalytic activity, photovoltaic performance, and photoconductivity response of ZnO NWs, thereby suggesting a strategy for tailoring the ultrafast carrier dynamics in ZnO NW-based devices.

Original languageEnglish
Pages (from-to)3075-3082
Number of pages8
JournalPhysical Chemistry Chemical Physics
Volume14
Issue number9
DOIs
Publication statusPublished - 28 Feb 2012
Externally publishedYes

ASJC Scopus subject areas

  • Physics and Astronomy(all)
  • Physical and Theoretical Chemistry

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