Zinc oxide set to change optoelectronics

Researchers at the University of Auckland have taken the first step towards developing the next generation of optoelectronic materials for use in devices such as screen displays, solar cells and lasers which display information using electrical signals and light emission.

Prof Wei Gao and his group, in the Faculty of Engineering's Department of Chemical and Materials Engineering, have 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 semiconductor and emits light.

"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 devices."

Prof Gao, who started to research the properties of zinc oxide about five years ago, says his team has developed an n-type conducting zinc oxide with good photoluminsecence, which gives very sharp UV radiation or red or green colour light, when it is 'excited' with a laser signals.

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 conducting zinc oxide which, says Prof Gao, is a much bigger challenge.

"We have good light emission using laser to excite the n-type zinc oxide. This is all right 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 optoelectronic devices.

Zinc oxide, he says, will be cheaper than existing optoelectronic 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 Prof 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.