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JILA is a joint institute of the National Institute of Standards and Technology (NIST) and the University of Colorado at Boulder. The research was conducted with collaborators from NIST’s Boulder campus and Matheson Tri-Gas in Longmont, Colorado.
The research, described in a paper by K.C. Cossel et al. entitled ‘Analysis of Trace Impurities in Semiconductor Gas via Cavity-Enhanced Direct Frequency Comb Spectroscopy’( Applied Physics B. Published online July 20) used a NIST/CU invention called cavity-enhanced direct frequency comb spectroscopy (CE-DFCS).
It consists of an optical frequency comb (a tool for accurately generating different colors, or frequencies, of light), adapted to analyze the quantity, structure and dynamics of various atoms and molecules simultaneously. The technique offers a unique combination of speed, sensitivity, specificity and broad frequency coverage.
The semiconductor industry has long struggled to find traces of water and other impurities in arsine gas used in manufacturing of III-V semiconductors for light-emitting diodes (LEDs), solar-energy cells and laser diodes for DVD players. The contaminants can alter a semiconductor’s electrical and optical properties.
For instance, water vapor can add oxygen to the material, reducing device brightness and reliability. Traces of water are hard to identify in arsine, which absorbs light in a complex, congested pattern across a broad frequency range. Most analytical techniques have significant drawbacks, such as large and complex equipment or a narrow frequency range.
The JILA comb system, previously demonstrated as a “breathalyzer” for detecting disease, was upgraded recently to access longer wavelengths of light, where water strongly absorbs and arsine does not, to better identify the water. The new paper describes the first demonstration of the comb system in an industrial application.
In the JILA experiments, arsine gas was placed in an optical cavity where it was “combed” by light pulses. The atoms and molecules inside the cavity absorbed some light energy at frequencies where they switch energy levels, vibrate or rotate. The
comb’s “teeth” were used to precisely measure the intensity of different shades of infrared light before and after the interactions. By detecting which colors were absorbed and in what amounts—matched against a catalog of known absorption signatures for different atoms and molecules—the researchers could measure water concentration to very low levels.
Just 10 water molecules per billion molecules of arsine can cause semiconductor defects. The researchers detected water at levels of 7 molecules per billion in nitrogen gas, and at 31 molecules per billion in arsine. The researchers are now working on extending the comb system even further into the infrared and aiming for parts-per-trillion sensitivity.
The research was funded by the Air Force Office of Scientific Research, Defense Advanced Research Projects Agency, Defense Threat Reduction Agency, Agilent Technologies, and NIST.
Honda Soltec Markets 120W & 130W CIGS Modules
The solar cell modules will be used for residential applications and are being marketed alongside a new power conditioner with a rated output of 5.5kW.
Honda Soltec, Honda’s wholly-owned solar cell subsidiary, has begun to sell two new residential- use solar cell modules with maximum output of 130W and 120W. The firm is also marketing a power conditioner with rated output of 5.5kW, adding to its lineup of home-use modules.
The firm has advanced its solar cell production technology to improve the quality of the electricity- generating layer. As a result, the new 130W solar cell module achieves solar energy conversion efficiency of 11.6%. This, says Honda, is the highest efficiency CIGS-based solar cells currently being sold in Japan.
Honda Soltec’s solar cells use thin film made from a compound of copper, indium, gallium and selenium (CIGS), making it environmentally responsible both in the manufacturing process and in use. The company began production and sales of solar cell modules for residential use in 2007 and for public/ industrial use in 2008.
August/September 2010
www.compoundsemiconductor.net 67
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