TY - GEN
T1 - The role of surface states in a-axis GaN nanowires
AU - Chin, Alan H.
AU - Ahn, Tai S.
AU - Li, Hongwei
AU - Vaddiraju, Sreeram
AU - Bardeen, Christopher J.
AU - Ning, Cun-Zheng
AU - Sunkara, Mahendra K.
PY - 2007
Y1 - 2007
N2 - 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.
AB - 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.
KW - Nanowires
KW - Photoluminescence
KW - Surface states
KW - Time-resolved photoluminescence
UR - http://www.scopus.com/inward/record.url?scp=42149150937&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=42149150937&partnerID=8YFLogxK
U2 - 10.1117/12.732222
DO - 10.1117/12.732222
M3 - Conference contribution
AN - SCOPUS:42149150937
SN - 9780819467874
T3 - Proceedings of SPIE - The International Society for Optical Engineering
BT - Nanophotonic Materials IV
T2 - Nanophotonic Materials IV
Y2 - 26 August 2006 through 27 August 2007
ER -