Crystal IS launches 2-inch AlN substrates
Crystal IS, a III-nitride materials start-up based in Green Island, NY, has released 2-inch diameter single-crystal AlN substrates onto the market for the first time.
The company is hoping that the move will help to spur the commercialization of AlGaN-based devices for both optoelectronic and microelectronic applications, which many believe will become a large market in the near future.
For example, AlGaN structures are being developed to produce ultraviolet-emitting LEDs that could be used to purify water or air (see related story). Another potential application is optical detection of harmful biological species. Because AlN has a good lattice match to AlGaN device layers, and a relatively high thermal conductivity, it should result in higher-performance, more reliable products than are currently available.
Although Crystal IS and The Fox Group have released AlN material in the past (see related story), these wafers have typically been much smaller in diameter, whereas the 2-inch material could potentially be used in volume device production.
At the moment, only 50% of the 2-inch wafer area is usable, a proportion that the Crystal IS team is working to increase towards 100%.
Crystal IS CEO Ding Day told Compoundsemiconductor.net that the latest substrates have a defect density of less than 104 defects/cm2, although Crystal IS also produces custom material for its clients with different specifications.
"Alternative techniques do exist to produce quasi-bulk AlN substrates, but these all involve growing on non-native materials and result in high defect densities more than 100,000 times that of the native substrate," said Day. "We are following in the footsteps of silicon carbide, [but] aluminum nitride is a very challenging material."
Growing single-crystal AlN is the biggest challenge, and Crystal IS has been awarded US patents that detail the use of a tungsten crucible to do this. The method quoted in US patent 6,770,135 describes how the growth chamber is first evacuated and then pressurized to about 1 bar with a gas mixture consisting 95% nitrogen and 5% hydrogen. A polycrystalline AlN seed is then placed in the growth chamber and heated to around 1800 deg C, resulting in a crystal that can be grown at 0.6-0.9 mm per hour.
Day added that Crystal IS is currently expanding its manufacturing facility by adding more custom-designed furnaces for AlN substrate growth. The company, which employs around 20 people, is close to completing its second funding round, expected to be worth $7 million.