Technical Insight
Crystal IS primed to seize UV LED market
As UV LED markets gather momentum, Crystal IS has launched the first commercial AlN-based LEDs. Will LED makers choose these over existing sapphire-based alternatives, asks Compound Semiconductor.
With UV LED markets poised for massive growth, device manufacturers are getting ready to deliver low-cost, high performance LEDs based on AlN substrates
In a bid to capture ultraviolet LED market growth, US-based manufacturer of AlN substrates and UV LEDs, Crystal IS, recently launched its so-called Optan UVC LEDs.
Described as the first commercial semiconductors based on native AlN substrates, the devices emit light between 250 and 280 nm, perfect for disinfecting water, sterilising surfaces, monitoring chemicals in pharma-manufacturing and other analytical applications. Hari Venugopalan, director of global product management at Crystal IS, anticipates strong industry demand.
"Customers have told us that they've found the performance of sapphire-based LEDs to be somewhat limited," he told Compound Semiconductor. "[Here] significant lattice mismatches introduce defects, limiting performance and lifetime."
"But with our native AlN substrate, we've reduced defect density by five orders of magnitude, so our products provide light output that is five times higher and with significantly longer lifetimes," he adds.
Indeed, at a maximum drive current of 100mA, Venugopalan reckons a typical LED lifetime comes in at 3000 hours. "But you know, we deliver so much light that drive currents can come down to 20mA and lifetimes will exceed 7000 hours," he says.
Meanwhile, sapphire-based UVC LEDs struggle to match the 2000 hour lifetimes typically provided by today's well-used deuterium and xenon flash lamps, depending on the specific application. And crucially the company claims its LEDs are actually cheaper than these broad spectrum UV lamps.
As Venugopalan explains, UV lamps supply light at multiple wavelengths, requiring band pass filters and optics to suppress unwanted wavelengths. This approach raises overall system cost, and can also reduce the intensity of the desired wavelength, reducing measurement accuracy.
In contrast, UVC LEDs offer a light source where light is emitted at, or close to, the required wavelength; so no need for extra optics. And according to Venugopalan, Crystal IS's devices offer better light stability during measurements, compared to sapphire-based alternatives.
"In instrumentation, this is really important and our LEDs have excellent spectral quality," he says. "Customers tell us that when they benchmark our LEDs against a sapphire LED, they see a narrow peak far superior and without the secondary peaks they see with sapphire alternatives."
Cutting costs
Crystal IS now claims its LEDs can cost 50% less than broad spectrum UV lamps, given the ancillary equipment demanded by these systems. But clearly another key way to cut costs, is to grow epi-layers on larger diameter wafers.
As Venugopalan confirms, his company is currently using one inch wafers but is transitioning to two inch bulk AlN. "We are quickly scaling up to a larger optoelectronic grade AlN substrates to reduce the manufacturing cost," he says.
"There are not so many manufacturers of commercial-grade or optical-grade AlN wafers, which could raise [supply chain] concerns in the industry, but we are now supported by a larger parent company [Asahi Kasei]," he adds. "This company is set up to handle demand from our customers and we will be establishing a stable, large volume AlN manufacturing output."
Optan LEDs target analytical instrumentation applications [Crystal IS]
Indeed, chemical manufacturing heavyweight, Asahi Kasei - which acquired Crystal IS in late 2011 - is currently building a trial production line to manufacture the UVC LEDs in Fuji, with all production materials being purchased from Crystal IS. Venugopalan says the company is already seeing demand for its UVC LEDs in analytical instrumentation and environmental monitoring but expects growing demand from disinfection applications.
"We have enough performance right now to replace UV lamps in niche markets within water disinfection and we shall see this soon, starting early next year," he says. "We're qualifying the LEDs, and doing lifetime and reliability tests, and once that's complete we will be able to go after this market."
"You know, this market is so much bigger than instrumentation, so even just addressing the niche sectors will be very significant for us," he adds.
And of course, this makes the move from one inch to two inch, and eventually four inch, AlN wafers, all the more critical.
"The larger substrate sizes will open up more and more sectors of the water disinfection market," says Venugopalan. "Whoever makes the optoelectronic-grade AlN in scale will be the winner, and we believe we are on track to do that."
