UNSW BREAKTHROUGH PROMISES MICROELECTRONICS REVOLUTION

UNSW researchers have made a breakthrough that has the potential to revolutionise the global computer and telecommunications industries.

They have produced a new technique for silicon to emit light. This means devices like microchips will be able to convert electrical signals directly into light signals, making it easier for them to send signals to each other. It will also simplify transmission down optical fibres, removing the need for relatively expensive and largely incompatible optical switches.

The breakthrough has been made by Professor Martin Green and Drs Jianhua Zhao and Aihua Wang of the Photovoltaics Special Research Centre, and Professor Michael Gal and PhD student Peter Reece of the School of Physics.

The results of their first experiment in this field have been reported in Nature ("Efficient silicon light-emitting diodes", 23 August) and indicate, essentially for the first time, that the long-dreamed-of goal of integrating light-emitting diodes (LEDs) directly into microchips could become a reality. This would streamline the link between two of the world's biggest industries: microelectronics and telecommunications.

"Researchers have long known that any material capable of absorbing light was also capable of emitting light. This was predicted by Kirchoff in 1860. We have applied this concept to silicon diodes to produce efficiencies between 10 and100 times higher than other groups," Professor Green said.

"Our results show that silicon can operate as an efficient LED. We obtained an efficiency above 1 per cent and, comparable to more conventional LEDs. This is sufficient to allow silicon LEDs to be incorporated into silicon computer chips.

"This was our first attempt at reversing the photovoltaic effect, that is at converting electricity into light. I believe its success was due to the knowledge we have gained from over 25 years of research at UNSW into all aspects of the photovoltaic process.

"Much work remains to be done but we believe this opens up a new window of opportunity for Australia. The global computer industry is worth billions, perhaps trillions, of dollars a year. The telecommunications industry is worth about the same. The solar PV industry is coming off a very small base but has the potential to match the computer and telecoms industries.

"We don't expect the rest of the world to stand around watching as we take this development further. We will have to act quickly and decisively if this breakthrough is to bring us the benefits I would like to see Australia gain from this research.
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"For many years the solar cell industry has been taking advantage of the findings of the intense research done by the world microchip industry to lower the cost and improve the efficiency of solar cells. Even though we have been seeking quite different results to those wanted by the microchip industry, we are all working with silicon.

"Now we have been able to turn the tables and give the microchip industry something to work with," he said.

A second benefit of the group's finding is that the light is produced by a very small wattage, the level of power at which microchips presently operate. The efficiency of the silicon device approximates to efficiencies obtained only 10 years ago from more complicated semiconductor devices made from gallium arsenide and similar materials.

Professor Gal, who confirmed the breakthrough with a series of measurements with Peter Reece, said: This result has major implications for the IT industry. Information technology is built on two technologies: microelectronics and photonics. In the past these have been separate technologies. This shows that now they can be integrated into a single technology," all built on a silicon chip.

"These are exciting times for physics. More breakthroughs as important as this can be expected and I agree with Martin that Australia has a real opportunity to gain from this result," he said.

A patent has been taken out on the process and UNSW has given funding for a high throughput testing laboratory.

CONTACT DETAILS: Professor Green, UNSW Photovoltaics Special Research Centre on (02) 9385 4018 or 0411 492 416; Rory McGuire at Renewables Etc on 0413 930 728; Amanda Hainsworth, UNSW Public Affairs and Development, (02) 9385 2873.

Date issued: 24 August 2001

ADDITIONAL INFORMATION
The breakthrough comes little more than a year after the Photovoltaics Special Research Centre was established by the ARC at UNSW to explore novel ways of raising the efficiency of photovoltaic (solar) cells from the present practical limit of about 30 per cent to the maximum theoretical limit of about 93 per cent.

Solar cells work by converting sunlight directly into electricity. When light is absorbed by silicon (or other photovoltaic materials, of which there are many), the light travels through the silicon until it either hits the right part of the silicon crystal and dislodges an electron, or it fails to do this and the light energy is converted into undesirable heat energy, or the light escapes.

When light dislodges an electron this creates a "hole" which can be thought of as a place where an electron "should" be but isn't. By flipping from one electrical bond between adjoining silicon atoms these holes can be made to move. A solar cell works by making the holes move in one direction and the freed electrons in the opposite direction, so using two processes to generate an electric current.

This new light generating effect (electroluminescence) does the opposite. It encourages a free electron to fall back into the hole. In physical terms the electron falls to a lower energy level and to do this the electron must release some energy. Previously, this energy has been largely wasted as heat energy but the UNSW group has been able to "tune" or manipulate the conditions inside the silicon crystal so this energy is released as light.