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MOCVD Keeps Chips Slim And Cool

Laser and LED chips look set for surprise benefits from recent improvements in GaN epitaxy, in the form of bismuth telluride growth for thermal management.

Thermoelectric cooler manufacturer Nextreme is setting new performance and size standards with its bismuth telluride-based devices, through its use of the latest MOCVD techniques.

The North Carolina company s eTEC coolers are currently in qualification with customers ranging from laser and LED makers to PC chip manufacturers and beyond, with commercial production scheduled for the beginning of 2008.

Nextreme claims that eTEC can deliver a maximum heat flux of up to 400 W/cm2, compared to just 10-20 W/cm2 for typical competing bulk TECs.

This, and the slimline 10-20 micron profile of the eTEC s active region, come thanks to Nextreme s epitaxial capability, which the company's vice-president of engineering, Dave Koester, says “is essentially very similar to the reactors used for commercial gallium nitride deposition".

“Gallium nitride has really driven MOCVD technology in the last five years, and we're benefiting from that knowledge," Koester explained.

Makers of luminescent devices with temperature-dependent wavelengths, or whose spectral output has been limited as they previously couldn't remove enough heat, are amongst those who have been enticed by eTEC s performance - but addressing these markets means that the component has to be assured as top quality.

“We're seeing a lot of interest from laser diode manufacturers for virtually every market there is, telecom, industrial and high-power, so high reliability is an absolute must for our device," said Paul Magill, the company s vice-president of marketing and business development.

eTEC relies on the thermoelectric effect, which produces a temperature difference when an electric field is applied across two different semiconductors. In Nextreme s case, this consists of a p-n junction with a p-type bismuth telluride/antimony telluride composite integrated with n-type selenium-doped bismuth telluride.

Bismuth telluride has low thermal conductivity that prevents unwanted convective backflow to the cooled side of the device, making it a popular base material for thermoelectric coolers, or TECs, including those Nextreme is looking to replace.

“We make something today that looks like a standard TEC and that can be swapped out, and you d get the performance but with a much smaller footprint," said Magill.

However, he promises even greater benefits to customers who allow Nextreme to be involved in the package design from the start, so that eTEC can be even more intimately integrated.

"For the future we're working with customers directly to design our device in, in a way that's not currently done with TECs, which would open up new performance avenues," Magill said.

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