Novel Devices ♦ news digest
efficient. Colour performance of LCDs industry-wide has gone largely unchanged until now. 3M research data shows that devices with 3M QDEF-enabled wide colour gamut will be noticeably different from other standard LCD devices, prompting the human eye to dwell on the display longer than less-saturated displays.
QDEF utilises the light emitting properties of quantum dots to create an ideal backlight for LCDs, which is one of the most critical factors in the coluor and efficiency performance of LCDs.
Unlike conventional phosphor technologies such as YAG that emit with a fixed spectrum, quantum dots can actually convert light to nearly any color in the visible spectrum.
Pumped with a blue source, such as a GaN LED, they can be made to emit at any wavelength beyond the pump source wavelength with very high efficiency (over 90 percent quantum yield) and with very narrow spectral distribution (only 30 - 40nm FWHM.)
The real magic of quantum dots is in the ability to tune the colour output of the dots, by carefully controlling the size of the crystals as they are synthesised so that their spectral peak output can be controlled within 2nm to nearly any visible wavelength.
A quantum dot, which is 10,000 times narrower than a human hair, can be tuned to emit light at very precise wavelengths. This means display makers can create a highly-optimised backlight that only produces the exact wavelengths of red, green and blue light needed by an LCD for optimal colour and energy performance.
Trillions of these quantum dots protected by barrier film fit inside an LCD backlight unit. The new film replaces one already found inside LCD backlights, which means the manufacturing process requires no new equipment or process changes for the LCD manufacturer.
“Improving colour performance for LCDs with simple, drop-in manufacturing solutions will create a stunning new visual experience for consumers,” comments Jason Hartlove, president and CEO, Nanosys, Inc.
“Working together with 3M and utilising their outstanding design and supply chain capabilities will allow our quantum dot technology to be widely deployed across all product segments, ensuring availability to all customers,” he adds.
A new era of atomic-scale semiconductor devices
Scientists have demonstrated the semiconductor molybdenum sulphide can be grown in layers only one atom thick without compromising its properties
Researchers at North Carolina State University have developed a new technique for creating high-quality semiconductor thin films on the atomic scale where the films are only one atom thick.
The technique can be used to create these thin films on a large scale, sufficient to coat wafers that are two inches wide, or larger.
“This could be used to scale current semiconductor technologies down to the atomic scale, lasers, LEDs, computer chips, anything,” says Linyou Cao, an assistant professor of materials science and engineering at NC State and senior author of a paper on the work. “People have been talking about this concept for a long time, but it wasn’t possible. With this discovery, I think it’s possible.”
The researchers worked with molybdenum sulphide (MoS2), an inexpensive semiconductor material with electronic and optical properties similar to materials already used in the semiconductor industry.
However, MoS2 is different from other semiconductor materials because it can be grown in layers only one atom thick without compromising its properties.
In the new technique, researchers place sulphur and molybdenum chloride powders in a furnace and gradually raise the temperature to 8500C, which vaporises the powder. The two substances react at high temperatures to form MoS2. While still under high temperatures, the vapour is then deposited in a thin layer onto the substrate.
“The key to our success is the development of a new growth mechanism, a self-limiting growth,” Cao says.
MoS2 structure June 2013
www.compoundsemiconductor.net 185
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