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€2m Project Sets 2-inch Non-polar GaN Target

As well as a strong research theme aiming at understanding the "green gap", PolarCoN is stating bold aims for non-polar substrates and green lasers

A German-Swiss research team has begun work on its effort to match US and Japanese groups developing non-polar GaN material for high efficiency green laser diodes.

The three-year, seven-university, €2 million ($3.16 million) “PolarCoN" collaboration that started on May 1 has the ambitious aim of developing 2-inch non-polar GaN substrates. Currently non-polar substrates with sizes in the tens of millimeters are typically the largest available, from the likes of Kyma Technologies and Mitsubishi Chemical.

“A big difference you see between polar and non-polar GaN devices is that they use such small substrates," said Ferdinand Scholz, the project's spokesman. “We'd like to make a difference to that."

Scholz, a professor in the Institute of Optoelectronics at Ulm University, will use his HVPE expertise to grow bulk GaN crystals. This growth relies upon successful deposition of non-polar seeds on m-plane SiC or sapphire by MOCVD elsewhere in the collaboration.

The overall project is being funded by the German Research Foundation and the Swiss National Science Foundation with the aim of closing the “green gap". Devices in this region are hampered by intrinsic polarization fields in conventional GaN material that shift the resulting wavelength towards the blue.

Therefore beyond larger size substrates, PolarCoN s ultimate goals include producing an optically-pumped laser diode with an output wavelength above 500 nm using non-polar or semi-polar GaN. Another key goal is to use similar materials to make an electrically-pumped laser diode emitting blue light with a particularly low threshold density.

These practical goals may owe something to the involvement of Osram Opto Semiconductors, which Scholz says had an input into the overall project strategy. However industrial partners will only become officially involved when and if PolarCoN reaches its second stage in 2011.

In the meantime the project will bend all of its academic might, including highly-reputed optoelectronics centers like Technical University Berlin and ETH Zürich, to unravelling the poorly-known underlying causes of the green gap.

“Our project is very strongly defined as a basic research project," explained Scholz, “not only to reach the goal of a green laser but also to work on the fundamental understanding of all scientific issues related to this problem."

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