Technical Insight
Start-up produces blue LEDs using 'dismissed' technique
The Fox Group has developed a hydride vapor-phase epitaxy technique that produces medium-brightness blue LEDs, based on AlGaN/GaN structures, at a low cost, writes Tim Whitaker.
Despite it being largely dismissed as a viable technique for the growth of GaN-based LEDs, The Fox Group - a start-up LED manufacturer headquartered in Ripon, CA - has developed a production method for manufacturing such devices by hydride vapor-phase epitaxy (HVPE).
Using technology originally developed by Technologies and Devices International (TDI), The Fox Group has established a manufacturing facility in Montreal, Canada, and shipped its first order of 460 nm "FoxBlue" LEDs in mid-May of this year. The mid-brightness devices have remarkable color consistency and are extremely low-cost, thanks to the use of the HVPE growth technique.
The devices are AlGaN/GaN structures that do not contain indium or quantum wells. As such, they are not high-brightness devices; typical intensities are around 1000 mcd for narrow-beam-angle LEDs or up to 3 mW for dies. "We are not competing with the big players such as Nichia, Toyoda Gosei, Cree, Osram and Lumileds, or anyone else making high-brightness InGaN LEDs," said Barney O Meara, the company s vice-president.
Even so, the technology used by The Fox Group has three very strong advantages: the HVPE process is intrinsically low-cost; it is protected by a strong patent portfolio; and the LEDs have extremely good color consistency.
Color consistency"The dominant wavelength is typically 460 ± 1 nm across each wafer, from wafer to wafer and from week to week," said O Meara, who credits the incorporation of indium into InGaN/AlGaInN structures for the much larger variations in brightness and wavelength exhibited by these devices. "Even for such applications as Christmas tree or holiday lights, color consistency is a significant issue; for sign and message board manufacturers the problem is much worse."
The HVPE technology that is used to grow LEDs was developed by TDI, a wide-bandgap materials specialist company based in Silver Springs, MD. The Fox Group has an exclusive license for certain TDI patents relating to light-emitting devices, and the firm has advanced the technology from the research stage to a fully automated, reproducible manufacturing process.
The company is confident of its intellectual property position. "Besides the entirely different crystal growth process, Fox Group s LED structure is different and, we believe, non-infringing," said O Meara. "We have one or more patents pending in this regard, and we do not use a buffer layer."
So what has prevented other companies from growing GaN LEDs by HVPE? Jacques Pankove and colleagues at RCA Labs grew n-type GaN by HVPE more than 30 years ago, but used a metal junction for the p-side of their device. Successfully growing p-type material was one of the key factors in developing a viable growth technology, while the other was the ability to use aluminum in a quartz-tube reactor. The Fox Group is currently using industry-standard 2 inch sapphire wafers, although other substrates can also be used.
Compared with MOCVD, which is used by all other manufacturers of blue GaN-based LEDs, HVPE is estimated to reduce the consumption of ammonia by at least an order of magnitude. Also, HVPE uses pure metals as starting materials rather than metal-organic precursors, which are around 10 times as expensive per gram of metal. The fast growth rate of HVPE (up to 1 µm/minute) and the relative simplicity of the HVPE-grown device structure also help to further reduce the overall cost of the process.
Using technology originally developed by Technologies and Devices International (TDI), The Fox Group has established a manufacturing facility in Montreal, Canada, and shipped its first order of 460 nm "FoxBlue" LEDs in mid-May of this year. The mid-brightness devices have remarkable color consistency and are extremely low-cost, thanks to the use of the HVPE growth technique.
The devices are AlGaN/GaN structures that do not contain indium or quantum wells. As such, they are not high-brightness devices; typical intensities are around 1000 mcd for narrow-beam-angle LEDs or up to 3 mW for dies. "We are not competing with the big players such as Nichia, Toyoda Gosei, Cree, Osram and Lumileds, or anyone else making high-brightness InGaN LEDs," said Barney O Meara, the company s vice-president.
Even so, the technology used by The Fox Group has three very strong advantages: the HVPE process is intrinsically low-cost; it is protected by a strong patent portfolio; and the LEDs have extremely good color consistency.
Color consistency"The dominant wavelength is typically 460 ± 1 nm across each wafer, from wafer to wafer and from week to week," said O Meara, who credits the incorporation of indium into InGaN/AlGaInN structures for the much larger variations in brightness and wavelength exhibited by these devices. "Even for such applications as Christmas tree or holiday lights, color consistency is a significant issue; for sign and message board manufacturers the problem is much worse."
The HVPE technology that is used to grow LEDs was developed by TDI, a wide-bandgap materials specialist company based in Silver Springs, MD. The Fox Group has an exclusive license for certain TDI patents relating to light-emitting devices, and the firm has advanced the technology from the research stage to a fully automated, reproducible manufacturing process.
The company is confident of its intellectual property position. "Besides the entirely different crystal growth process, Fox Group s LED structure is different and, we believe, non-infringing," said O Meara. "We have one or more patents pending in this regard, and we do not use a buffer layer."
So what has prevented other companies from growing GaN LEDs by HVPE? Jacques Pankove and colleagues at RCA Labs grew n-type GaN by HVPE more than 30 years ago, but used a metal junction for the p-side of their device. Successfully growing p-type material was one of the key factors in developing a viable growth technology, while the other was the ability to use aluminum in a quartz-tube reactor. The Fox Group is currently using industry-standard 2 inch sapphire wafers, although other substrates can also be used.
Compared with MOCVD, which is used by all other manufacturers of blue GaN-based LEDs, HVPE is estimated to reduce the consumption of ammonia by at least an order of magnitude. Also, HVPE uses pure metals as starting materials rather than metal-organic precursors, which are around 10 times as expensive per gram of metal. The fast growth rate of HVPE (up to 1 µm/minute) and the relative simplicity of the HVPE-grown device structure also help to further reduce the overall cost of the process.
