Lasers ♦ news digest
constant of In0.1Ga0.9As. As a result, the wafer curvature does not change during the subsequent growth of In0.1Ga0.9As layer.
The authors call this final growth phase “free-standing” because the In0.1Ga0.9As layer grows with its natural lattice constant and creates a quasi-substrate similar to an In0.1Ga0.9As wafer for the later device growth.
With a buffer thickness of 1000 nm, further experiments with the same indium content and different buffer thicknesses showed that if the relaxation is not sufficient , the quasi- In0.1Ga0.9As substrate growth is compressively strained.
However, over-relaxation (1600 nm) results in a tensile strain.
The researchers plotted these changes to obtain a map of the correlation between thickness and curvature. For a free-standing quasi-InGaAs substrate, they choose a buffer thickness with no further variation in curvature over time during In0.1Ga0.9As growth.
This work shows that in-situ curvature measurements are a decisive part of an innovative technology that is developed to improve characteristics of LDs.
Ryo Nakao et al describe further details of this work in the EMS-32 proceedings (2013).
Sharp and Osram to take LEDs and lasers to the next
level A patent agreement between the two firms is expected to boost R&D in these markets and others
Sharp and Osram have entered into a patent cross-licensing agreement covering LEDs and laser diodes.
This cross-licensing agreement grants each party the right to use inventions related to LED and laser diodes covered by the patents owned by the respective companies around the world.
Both companies expect that this will spur their R&D and contribute to further advances in LEDs, laser diodes, and related industries.
Sharp began mass-production of LEDs in 1970 and the world’s first production of infrared laser diodes for CDs in 1982.
With these LED and laser diode technologies built up over the years, the company has recently come out with numerous unique devices, including a high-efficiency, high-brightness 100 W-class LED for lighting, and a red laser diode that can be used as a light source for displays.
Under this agreement, the companies’ mutual licensing of patents will allow each party to complement its respective technologies. Sharp and Osram believe this will accelerate development of high-performance LEDs and laser diodes and
have a positive effect on the creation of devices that match the needs of worldwide markets.
Measuring light amplification with polymers for next generation lasers
Using picosecond laser pulses diminishes thermal degradation to get a more accurate measurement of a material’s optical gain; this is vital for laser development
Researchers from North Carolina State University have developed more accurate measurements of how efficiently a polymer called MEH-PPV amplifies light.
This should advance efforts to develop a new generation of lasers and photonic devices.
“By improving our understanding of this material, we get closer to the longstanding industry goal of using MEH-PPV to create cheaper, more flexible photonic technologies,” says Lewis Reynolds, a teaching associate professor of materials science and engineering at NC State and senior author of a paper describing the research.
MEH-PPV is a low-cost polymer that can be integrated with silicon chips, and researchers have long sought to use the material to convert electricity into laser light for use in photonic devices such as optical amplifiers and chemical sensors. At issue is MEH-PPV’s ‘optical gain,’ which is a way of measuring how effectively a material can amplify light. Understanding a material’s optical gain is essential to laser development.
Researchers determine the optical gain of MEH-PPV by pulsing laser light into the material and measuring the light that the MEH-PPV then produces in response.
The NC State team used extremely short laser pulses – 10 laser pulses per second, with each pulse lasting only 25 picoseconds (25 trillionths of a second).
Previous efforts to determine MEH-PPV’s optical gain produced inaccurate results because they used laser pulses that lasted one thousand times longer.
“The longer pulses caused thermal degradation in the MEH- PPV, meaning they led to structural and molecular changes in the material,” says Zach Lampert, a former Ph.D. student at NC State and lead author of the paper. “Essentially, the longer laser pulses were heating the polymer. We were able to minimise these thermal degradation effects, and get a more accurate measurement, by using the picosecond pulses.”
“Our new approach is fairly straightforward and can be easily implemented elsewhere,” Reynolds says.
This work is described in detail in the paper, “Intrinsic optical gain in thin films of a conjugated polymer under picosecond excitation,” by Zach E. Lampert et al in Applied Physics
August/September 2013
www.compoundsemiconductor.net 111
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