Osram Opto's blue lasers live longer
The company attributes it progress largely to improvements in the quality of the InGaN quantum well active region of the devices. Osram Opto grows its laser structures on SiC substrates; this 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 help to remove the heat generated by the laser chip, improving its operating lifetime. The company has also brought its packaging experience from LED manufacturing to bear on the task of optimizing the chip mounting for maximum heat removal.
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 Harle, 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 which we must exploit to further reduce the operating voltage and operating current," said Harle.
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.