Finland excels in epitaxial growth

17 Jun 2002

The Optoelectronics Research Centre at Tampere University of Technology in Finland has had remarkable success in commercializing its research. Johan van der Linden finds out why.

From Opto & Laser Europe October 2001

Tampere University of Technology, Finland, is known to the optoelectronics community for its Optoelectronics Research Centre, which emerged from the university's semiconductor-physics department in 1999.

The centre develops III-V compound-semiconductor technology and receives approximately EURO 3 million per year in collaborative R&D grants and contracts - 80% are from outside the university's budget.

The Optoelectronics Research Centre (ORC) co-operates with more than 30 firms and universities worldwide and promotes the establishment of new businesses, such as Tutcore, Finland, which develops laser diodes; Modulight, Finland, which makes semiconductor optoelectronic components; and a subsidiary of French firm Memscap, which specializes in resonant-cavity LEDs.

Markus Pessa, director of ORC, said: "We concentrate on developing technologies rather than the basic physics, so it is not surprising that our team sets an example of how to convert research results and strategically important ideas into commercial products." With its five commercial molecular-beam-epitaxy (MBE) reactors, ORC ranks among the biggest university-based MBE research centres in Europe. "In 1991, I proposed the establishment of Tutcore because we received an increasing number of inquiries from abroad about the possibility of supplying custom-designed epiwafers," said Pessa.

Tutcore had started building its own cleanrooms in the mid-1990s when several companies showed an interest in buying the start-up. At the end of 1996, 80% of the shares were eventually sold to Coherent, in the US, which saw an opportunity to complement its high-power-laser expertise with semiconductor components.

Harry Asonen, CEO of Tutcore, said: "While many firms were manufacturing 980 nm pump lasers, we initiated the development of high-power devices."

Tutcore's key scientists had all gained expertise at Tampere University of Technology (TUT) and they were the only team in serious pursuit of a high-power aluminium-free InGaAsP laser diode at that time.To make efficient high-power lasers viable, the amount of heat generated in the semiconductor needs to be significantly reduced. InGaAsP has a quantum efficiency of 55% compared with 45% for AlGaAs, and it is a better conductor of heat, which is why aluminium-free laser diodes exhibit greater wavelength stability with increasing temperatures. This is especially important when multiple laser diodes are combined in a laser bar - for which Tutcore has developed a proprietary microchannel cooling architecture - to deliver high power.

The material science of InGaAsP, however, is difficult to master. "The commercial metal-organic chemical-vapour-deposition (MOCVD) process used by most firms in the optoelectronics sector is much less mature for growing aluminium-free high-power devices," stated Asonen. "With MBE, the alloy-composition profile and doping level can be controlled across a wafer, from wafer to wafer, and from run to run," he added. It is clear that these features come at a price: MBE technology is significantly more expensive than MOCVD.

Tutcore employs more than 50 scientists, engineers and technicians, and had a turnover of approximately EURO 10 million in 2000. Coherent manufactures stacked modules of multiple laser-diode bars that are sold through Tutcore and lead the industry in power density to serve a number of different end-user applications.

Recently, Coherent's Finnish division produced 980 nm VCSEL-based pump-laser diodes. These are single-mode fibre pigtailed at Coherent in the US. The output power from the fibre is 500 mW, but there is serious potential for growth, says Asonen.

Over the years, the team at ORC has continued to work on application-driven research topics with the focus on laser diodes, resonant-cavity (RC) LEDs and solar cells. It is developing edge-emitting lasers that oscillate in the 600 to 1600 nm range and AlGaInAs and nitrogen-diluted GaInAsN/GaAs-based components for fibre-optic data-transmission systems.

The newest fields of research at ORC are the design, growth and fabrication of VCSELs, and 650 and 1000 nm RC-LEDs for polymer optical-fibre-based communications systems.

In June, Memscap Oy was formed by Memscap SA of Grenoble, France, in the framework of a research co-operation agreement with ORC to jointly develop a series of RC-based light sources for polymer optical-fibre-based short-haul communications systems. A new high-volume production facility is planned at Hermia, Finland, and should be completed within the next 18 months.

ORC is also working on advanced multi-junction solar cells that exhibit high conversion efficiency, good radiation resistance and an improved power-to-weight ratio. Four double-junction GaInP/GaAs solar cells are being tested on the Equator-S satellite, which is in low orbit around the Earth.

ORC's expertise in MBE growth is being extended to GaN-based semiconductor light sources in the blue and ultraviolet regions by applying a novel approach that uses higher than normal growth temperatures.

The growth of telecoms applications spawned new start-up Modulight in May 2000. The company specializes in high-performance semiconductor optoelectronic components and employs more than 20 people. Its production facility at Hermia will become operational in September.

Modulight's biggest shareholder is French firm PicoGiga, which specializes in electronic components for wireless communications and is based in "Optics Valley" in France.

Petteri Uusimaa, CEO of Modulight, said, "Our products are intended for the metropolitan and access sections of the optical-network layer, where they will provide increased capacity, flexibility, scalability, and cost-effectiveness."

Modulight will design and fabricate the core parts of basic network elements, such as light transmitters and receivers. "One of our key competences is in the smooth interface between epitaxial growth and device processing, which allows for short turn-around times in the product-development phase," Uusimaa added.

The company will start volume production of 1310 nm Fabry-Pérot laser diodes for uncooled 2.5 Gbit/s operation at the end of this year. In the short term, 10 Gbit/s lasers operating at 1310 and 1550 nm, and high-sensitivity avalanche photodetectors will be added to the firm's portfolio."I am glad to see that Finnish research-funding organizations have realized how fast the compound-semiconductor industry is developing," said Pessa.

One indication of this awareness is that the TE-Centre [a local-development organization belonging to the Finnish Ministry of Trade and Industry] of the Tampere district granted ORC almost EURO 1.5 million for the next two years to coordinate R&D on compound semiconductors, optoelectronics and fibre-optical communications.

"There are now more than 10 MBE reactors within 2 km of ORC, representing perhaps the highest density of MBE systems in Europe. ORC and its spin-offs want to remain in the mainstream, but this means that one must work hard and be nimble to survive," Pessa concluded.

Hermia www.hermia.fi

ORC www.orc.tut.fi

Tutcore www.tutcore.fi

Modulight www.modulight.com