German firm CrystAl-N is producing aluminium nitride (AlN) substrates for fabricating specialist ultraviolet lasers and LEDs.
Most blue and violet LEDs are made on sapphire or SiC substrates.
For wavelengths shorter than 300nm, the dislocation density in sapphire is very high,” company CEO Paul Heinmann told Electronics Weekly. “The physics says epitaxy on AlN shows decreased dislocation density and therefore increased light output.”
Unlike most semiconductor wafer materials, which can be draw from melted raw material, AlN has to be grown from vapour.
“The problem with AlN is that you cannot grow from a melt as it decomposes, so you have to grow it from a gas at 2,200°C.
He likens deposition to water vapour condensing on a bathroom mirror.
“It is a sublimation-recombination process,” said Heinmann. “you heat the raw material to 2,400°C and have a seed crystal at 2,200°C where single crystal AlN condenses.
Typically, 10x12mm rectangular substrates are produced.
“With pure AlN you can make LEDs down to 210nm wavelength, so you can get 210-350nm by replacing Al with Ga depending on the combination,” said Heinmann.
Applications for short wavelength UV include sterilising water supplies, air-conditioning and Curing of varnishes, inks and polymers.
Currently, customers are mainly research institutes.
“We are looking for strategic partners to develop applications in LEDs, lasers, RF devices and high-power transistors,” said Heinmann.
CrystAl-N was founded in 2010 as a spin-off from the materials science department of Erlangen University in Germany where bulk AlN crystals have been grown for over 10 years.
