Better and less expensive LED lights

The Nobel Physics Prize was awarded this year to Isamu Akasaki, Hiroshi Amano and Shuji Nakamura for the development of the blue LED light in the 1990s.

When the trio's invention was combined with the earlier developed red and green lights, the result was a white LED light. The many gleaming light sources that use these LEDs are now almost everywhere, and it's no wonder: compared to incandescent and fluorescent lamps the LED is insurmountable in terms of both length of use and energy efficiency,

But there is room for improvement even in the LEDs. Since the beginning of the millennium, Aalto University has developed better materials and production methods. Professor Filip Tuomisto leads a team that studies, among other things, point defects in the semiconductor materials used in LEDs.

‘Point defects are interruptions in the periodic structure at the atomic level. An atom may be missing or in the wrong place, and these errors determine to a large extent the properties of the semiconductor and therefore also those of the LED,’ he explains, and highlights the importance of positron annihilation spectroscopy as a research method.

‘It is indeed a monster of a name,’ he laughs.

‘Positron annihilation spectroscopy probes lattice defects at the atomic level, their quality and quantity. We are among the best in the world at using this technique. We collaborate with a large number of research groups synthezing and processing semiconductor materials, including the recent Nobel Prize winners, with whom we are also the only university in Finland to have produced joint publications.’

We collaborate with a large number of research groups synthezing and processing semiconductor materials, including the recent Nobel Prize winners.

LED lights are conventionally produced on expensive sapphire wafers.  Professor Harri Lipsanen has set his sights on finding both better and less expensive production methods and also new LED structures. Aalto University has invested significantly in this over the years by, for example, carrying out cooperative work between the School of Electrical Engineering and the School of Science as part of the Aalto Energy Efficiency programme, and providing funding for large investments in equipment.

‘The silicon wafer is clearly less expensive as a substrate than one made of sapphire, but it is also harder to produce. The gallium nitride wafer, on the other hand, is interesting because the material produced on it is of the best quality,’ he says.

According to Mr Lipsanen, the research carried out with LEDs around the world has produced great results. Efficiency has increased and durability has improved to such an extent that street lamps or car lights do not need to be changed at all.

In addition to their use for lighting, blue LEDs and the similar ultra-violet LEDs have other uses too. For example, blue-ray discs require the use of a laser produced from the same material.

‘Ultraviolet LED light can also be used to purify water. This has been researched at Aalto in cooperation with Helsinki University and Lappeenranta University of Technology,’ Mr Lipsanen explains.

Prize already awarded earlier to the blue LED

In 2006 the Technology Academy Finland (TAF) awarded the Millennium Technology Prize to Shuji Nakamura for the development of the blue LED. Mr Nakamura presented in 1993 the first sapphire blue LED, which later led to the creation of the white LED.

With the Millennium Technology Prize Finland pays tribute to innovations that improve life. The value of the prize is one million euros. TAF is backed by the Finnish science community, the state administration, and the business sphere. Aalto University works as a strategic partner of the Technology Academy.