New material poised to revolutionise opto-electronics

New material poised to revolutionise opto-electronics

Professor Gao (right) and Dr Li depositing zinc oxide
onto glass substrates.

Researchers at The University of Auckland have successfully
taken the first step towards developing a new generation of opto-electronic
materials for use in devices such as screen display, solar cells and lasers
which display information using electrical signals and light emission.

Professor Wei Gao and his group, in the Faculty of Engineering’s
Department of Chemical and Materials Engineering, has developed a technique
to make a very fine film of zinc oxide on substrates of glass, silicon and
metal, which acts as a conductor or semi-conductor and emits light.

“Zinc oxide is very strange stuff. It’s cheap and is used
as powder filler in oil and water-based white paint,”says Professor Gao.

“But what makes it really unusual is that you can run
an electrical current through it, and it can be transparent with special
light-emitting properties. These properties don’t usually occur together,
for instance, metals are conducting but not transparent, while glass is transparent
but not conducting. This makes it suitable for use in many kinds of electronic

Professor Gao, who started to research the properties
of zinc oxide about five years ago, says his team has developed a n-type
(negative) conducting zinc oxide with excellent photoluminescence, which
gives very sharp UV radiation or red or green colour light, when it is “excited”
with a laser signal.

But further work is needed to better control the properties
of the n-type zinc oxide and to get stable light emission. The recent award
of a Marsden grant, will take the project to the next stage, developing
a p-type (positive) conducting zinc oxide which, says Professor Gao, is a
much bigger challenge.

“We have good light emission using laser to excite the
n-type zinc oxide. This is alright in the laboratory, but for application
in electronic devices, we need to use an electrical signal. To do that we
need to create a p-n junction, which will enable us to apply an electrical
signal to get the light we want.”

If successful, Professor Gao says zinc oxide will become
the base material for the next generation of opto-electronic devices, revolutionising
the industry in the way silicon – now used everywhere in the world for silicon
chips – revolutionised information and communications technology.

Zinc oxide, he says, will be cheaper than existing opto-electronic
materials and has the potential to make visual display surfaces brighter
and the colour easier to control.

But, he says, the research is complex as it is not yet
well-understood why it is difficult to form p-type zinc oxide using traditional
methods. A senior researcher in Professor Gao’s group, Dr Zhengwei Li, is
using a special technique to make p-type zinc oxide – oxidation of zinc thin
films at an extremely low oxygen partial pressure.

Together, with Dr John Kennedy at the Institute of Geological
and Nuclear Sciences and Dr Roger Reeves at the University of Canterbury,
Professor Gao says, the team will be applying innovative technology, developed
within the Faculty of Engineering, to address the problem.

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