17 Oct 2002
Osram Opto Semiconductors reports a steady improvement in the lifetime of it gallium-nitride-based blue lasers.
Germany-based Osram Opto Semiconductors has increased the service life of its GaN-based blue lasers from two minutes to 143 hours of continuous-wave operation. The company anticipates market-ready devices will be available in July 2005 if the current rate of progress is maintained.
According the Osram Opto, this progress is largely due to improvements in the quality of the indium-gallium-nitride (InGaN) quantum well active region of the devices. The company grows its laser structures on silicon-carbide (SiC) substrates, which provides a better lattice match to GaN and has a higher thermal conductivity than the sapphire substrates that are widely used for GaN epitaxy.
SiC's thermal properties improve the lifetime of the device by removing the heat generated by the laser chip. The company is also using its packaging experience from LED manufacturing to help optimize heat removal from the chip mounting.
Osram Opto say that thanks to a new contacting process the operating voltage of its blue lasers has been halved from 16 to 8 V. Other improvements, including smoother laser mirrors, have helped to reduce the operating current to 96 mA. Output power is currently 1 mW.
According to Volker Härle, head of development for InGaN devices at Osram Opto, the potential for optimization has not yet been exhausted. "There are still opportunities in the areas of epitaxy, chip technology and assembly that we must exploit to further reduce the operating voltage and operating current," said Härle.
The work at Osram Opto is part of a project sponsored by the German government that started in August 2001. Other partners in the project include Fraunhofer Institute for Solid-State Physics in Freiburg and the universities of Brunswick, Regensburg, Stuttgart and Ulm. The goal of the project is to produce a prototype blue laser by July 2004. If current progress is maintained, then a market-ready product is anticipated by July 2005.
However, the project is someway behind the benchmarks set by others around the world. SiC substrate manufacturer Cree also has a blue laser development program and grows the structures on its SiC substrates. In February this year Cree announced that its 405 nm, 3 mW lasers had achieved a projected lifetime of 10 000 hours.
Nichia already sells blue lasers commercially and broke the 10,000 hour lifetime barrier October 1997. The company grows its LED and laser structures on sapphire substrates.
Jon Newey is technology editor of Compound Semiconductor magazine.