news digest ♦ Lasers
Faced with a high excited electronic state requirement and destructive crosstalk in a densely packed layer, previous groups have needed to pump their dots with a lot of power to push them past a higher threshold for producing light amplification, a core element of any laser.
Pumping them intensely, however, gives rise to another problem: an excess of excited electronic states called excitons. When there are too many of these excitons among the quantum dots, energy that could be producing light is instead more likely to be lost as heat, mostly through a phenomenon known as the Auger process.
The nanocrystals’ structure and outer cladding reduces destructive crosstalk and lowers the energy needed to get the quantum dots to shine. That reduces the energy required to pump the quantum dot laser and significantly reduces the likelihood of exceeding the level of excitons at which the Auger process drains energy away. In addition, a benefit of the new approach’s structure is that the dots can act more quickly, releasing light before Auger process can get started, even in the rare cases when it still does start.
“We have managed to show that it’s possible to create not only light, but laser light,” Nurmikko says. “In principle, we now have some benefits: using the same chemistry for all colours, producing lasers in a very inexpensive way, relatively speaking, and the ability to apply them to all kinds of surfaces regardless of shape. That makes possible all kinds of device configurations for the future.”
The US. Department of Energy, the Air Force Office for Scientific Research, and the National Science Foundation supported the research. Dang is a Vietnam Education Foundation (VEF) Scholar.
Further details of this work has been published in the paper,”Red, green and blue lasing enabled by single-exciton gain in colloidal quantum dot films”, by Dang et al, Nature Nanotechnology, 7, 335–339 (2012). DOI:10.1038/nnano.2012.61
VI Systems reveals 40 Gbit/s 850nm VCSEL with HAB pad contacts
The new product line of high speed 850nm gallium arsenide based VCSEL chips are compact and have an ultrahigh modulation rate VI Systems has launched a new product line for high speed VCSEL chips with a data rate of up to 40 Gbit/s. VIS’ new generation of high-speed 850 nm VCSELs and VCSEL arrays (1 x 4 and 1 x 12) feature an ultrahigh -3 dB modulation bandwidth of 20 GHz and a novel HAB contact pad design that overcomes the problems of thick and soft planarisation layers, characteristic to high-speed VCSEL designs, and enables ultra-robust bonding and packaging. VIS says its novel manufacturing approach and array designs are in compliance with the standard 250 µm device-to-device pitch (linear spacing) allowing systems developers to dramatically extend their capabilities in energy efficient data communication. Die-level samples are available now.
Global semiconductor sales escalate
A new report says silicon manufacturer Broadcom and compound semiconductor supplier TriQuint are good examples that illustrate that the semiconductor industry is bouncing back
The semiconductor stock market has not done too badly this year, thanks to the growing demand for tablets and smartphones.
The mobile market relies on both silicon and compound semiconductor devices although silicon dominates in many of these areas.
According to
ParagonReport.com, the Semiconductor Industry Association (SIA) recently reported worldwide semiconductor sales showed growth across all regions.
The organisation reported that for March 2012, worldwide sales of semiconductors totalled $23.3 billion, a 1.5 percent increase over the previous month. Sales in Europe and Japan grew 3.8 percent
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www.compoundsemiconductor.net June 2012
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