Quantum leap in research project:

Longer life for blue lasers

REGENSBURG - In the space of just one year the developers at Osram Opto Semiconductors have managed to increase the service life of blue gallium-nitride lasers in continuous wave mode from two minutes to 143 hours.

A significant factor in this success was the improvement in the quality of the single-crystal semiconductor layers in the production of gallium-nitride based structures on silicon-carbide substrates. On the basis of the metal organic vapour phase epitaxy process, they were able to stimulate controlled epitaxial growth of highly-developed, single-crystal structures with layer thicknesses of just a few nanometers, thus significantly improving the efficiency of the light generation process.

Clever management of the thermal balance
The high thermal conductivity of silicon-carbide has been utilized to improve the thermal balance of the chip, and it also prevents the chip from overheating during operation. Here, the developers at Osram Opto Semiconductors were able to bring in experience from high-end package technology in high-power laser assemblies, which ensures optimum heat dissipation and efficient decoupling of light. Thanks to new contact processes it has been possible to halve the operating voltage from 16 V to 8 V. Optimised chip technology which has been specifically tailored to the material system and features lateral optical wave guides and extremely smooth laser mirrors has made it possible to reduce the operating current to 96 mA.

However, Dr. Volker Härle, who is head of development for gallium-indium-nitride at Osram Opto Semiconductors, is sure that "the potential for optimisation 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." In addition, the defect density represents a real challenge to the specialist. This results from the varying distances between the atoms in the crystalline structure of the silicon-carbide substrate and the epitaxial aluminium-gallium-indium-nitride layers of the laser structure. "With the aid of suitable epitaxy processes, such as the ELO procedure (Epitaxial Lateral Overgrowth), the defects can still be reduced by several orders of magnitude", stresses Härle, "and last but not least we still need to improve the optical output power as well". At the moment this is 1 mW in cw mode.

The project, which is sponsored by the German Federal Ministry of Education and Research and has been running since August 2001, is taking place under the involvement of the developers at Osram Opto Semiconductors in Regensburg, the Fraunhofer Institute for Solid-State Physics in Freiburg and the universities of Brunswick, Regensburg, Stuttgart and Ulm. The stated goal of the project is to produce a prototype of the blue laser by July 2004. If current progress is maintained, then the parties involved in the project anticipate a market-ready product within approximately just one year of completing the project. Market research institutes also anticipate a corresponding demand at around this time (2004/2005). The key advantages in the use of the laser lie in its greater information density and memory density. This means that the technology will mainly benefit optical storage media such as DVDs or MiniDiscs, but also projection and media technology like beamers or Laser-TVs. Blue lasers could also be used in printers to replace existing light sources and achieve higher resolutions.

About Osram Opto Semiconductors
Osram Opto Semiconductors GmbH, Regensburg, is a subsidiary of Osram, one of the three largest lighting manufacturers in the world. It offers its customers solutions based on semiconductor technology for the lighting, sensor and visualisation sectors. The company has sites in Regensburg, San José (USA) and Penang (Malaysia). In the 2001 fiscal year (to the end of September) its 4000 employees produced sales totalling EUR 329 million. For more information go to www.osram-os.com .

Press contact:

OSRAM

Christian Bölling
Tel: +49-89-6213-2597
Fax: +49-89-6213-3457
Email: c.boelling@osram.com