Annual Report 2007 - The Australian Nanotechnology Network

optimisation of these nanowires and nanowire heterostructures, and ultimately the success of
nanowire-based optoelectronic devices.
Prior to the visit, I grew a series of GaAs nanowire samples to study (i) the effects of growth
temperature and precursor flow (ii) nanowire doping with Si, Zn and C (iii) the effects of
passivation with an AlGaAs shell and AlGaAs shell composition (iv) quantum confinement
effects within axial quantum wells of GaAs/AlGaAs nanowire superlattices and (v) quantum
confinement within GaAs/AlGaAs quantum well shells.
At UC, I spent many days and late nights in the lab obtaining results whilst ably assisted by UC
PhD students Thang Hoang, Melodie Fickenscher and Saranga Perera. We made several
interesting and important findings. Firstly, time-resolved PL studies revealed a long exciton
lifetime in GaAs nanowires grown at low temperature. This indicates that these low-temperature
grown nanowires have very high optical quality and should find further applications in
optoelectronic devices. Second, we found that intrinsic carbon doping decreases with increasing
arsine precursor flow rate and decreasing temperature, which indicates that highly pure material
can be obtained using high arsine flow rate and low temperature. Also, we obtained some
intriguing results from GaAs/AlGaAs quantum well shell samples which indicate exciton
confinement within quantum well shells. Many of these results will be submitted for publication
very shortly.
Under the guidance of the professors and PhD students at UC, I developed valuable experimental
skills: performing PL characterise my nanowire samples, learning to analyse and interpret the
data, and developing a detailed understanding of the physics of carrier relaxation in
semiconductor nanowires. The UC group has great expertise in this area and I gained a much
greater understanding of semiconductor optics. Furthermore, I learnt about the design and
optimisation of such optical characterisation systems. Having returned to ANU, I’m now
applying this knowledge to upgrade and optimise our own laboratory’s existing PL and micro-PL
systems.
Additionally, I presented a seminar to the UC group. This enhanced their understanding of
ANU’s work on nanowire fabrication
and characterisation. I believe that my
visit strengthened collaboration between
our groups, and now we’re in contact on
an almost daily basis.
It was an extremely productive trip. I
worked in a very active and stimulating
research environment, obtained
substantial experimental data and learnt
a great deal. The visit was so productive
that I extended the duration of my stay
from one month to two months!
Additionally, I had a fantastic time, met
many wonderful people and made some
lifelong friends. It was fun to experience
life in mid-West America and participate
in Halloween, Thanksgiving and Hannah Joyce with her hosts at the University of
Pre-Christmas shopping! I’m extremely Cincinnati
grateful to ARCNN for providing me this opportunity,
and to my kind, generous and extremely skilled hosts at UC.
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