The role of surface states in a-axis GaN nanowires

Alan H. Chin, Tai S. Ahn, Hongwei Li, Sreeram Vaddiraju, Christopher J. Bardeen, Cun-Zheng Ning, Mahendra K. Sunkara

Research output: Chapter in Book/Report/Conference proceedingConference contribution


GaN nanowires have been the subject of intense research lately, due to the many potential ultraviolet applications and interesting properties that they possess. Because GaN has an anisotropic wurtzite crystal structure, many of its properties are dependent upon crystal orientation. For example, the photoluminescence (PL) of GaN nanowires with growth direction along the a-axis is blue-shifted relative to the PL of wires with growth direction along the c-axis. However, the origin of the difference in PL between nanowire samples of different growth directions remains unclear. To determine if surface states play a role in the dependence of GaN nanowire photoluminescence on crystal orientation, we use time-integrated photoluminescence (TIPL) and time-resolved photoluminescence (TRPL) to study the PL from GaN nanowire samples of different crystallographic orientations. We observe temporal dynamics of the blue-shifted PL feature in the a-axis GaN nanowires that is suggestive of a surface trapping process occurring, where some fraction of electron-hole pairs are prevented from recombining via the band edge emission process because carriers diffuse to the surface where they are trapped before carrier relaxation to the band edge is complete. Once a carrier is trapped and localized at a surface trap state, light emission primarily occurs only when the complementary carrier diffuses to the same surface trap. We envision that a thin oxide layer forming at the surface introduces surface traps that cause the blue emission, and that the surfaces of the a-axis GaN nanowires are more susceptible to this oxidation than the c-axis GaN nanowire surfaces.

Original languageEnglish (US)
Title of host publicationNanophotonic Materials IV
StatePublished - 2007
EventNanophotonic Materials IV - San Diego, CA, United States
Duration: Aug 26 2006Aug 27 2007

Publication series

NameProceedings of SPIE - The International Society for Optical Engineering
ISSN (Print)0277-786X


OtherNanophotonic Materials IV
Country/TerritoryUnited States
CitySan Diego, CA


  • Nanowires
  • Photoluminescence
  • Surface states
  • Time-resolved photoluminescence

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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