compound semiconductor ♦ news digest

In recent attempts to grow semiconductor nanowires with “almost” arbitrary band gaps, the research team led by Ning and Pan, an assistant research professor, have used a new approach to produce an extremely wide range of band gaps.

They alloyed two semiconductors, zinc sulfide (ZnS) and cadmium selenide (CdSe) to produce the quaternary semiconductor alloy ZnCdSSe, which produced continuously varying compositions of elements on a single substrate (a material on which a circuit is formed or fabricated).

Ning said this is the first time a quaternary semiconductor has been produced in the form of a nanowire or nanoparticle.

By controlling the spatial variation of various elements and the temperature of a substrate (called the dual-gradient method), the team produced light emissions that ranged from 350 to 720 nanometers on a single substrate only a few centimeters in size.

The color spread across the substrate can be controlled to a large degree, and Ning said he believes this dual-gradient method can be more generally applied to produce other alloy semiconductors or expand the band gap range of these alloys.

To explore the use of quaternary alloy materials for making photovoltaic cells more efficient, his team has developed a lateral multi-cell design combined with a dispersive concentrator.

The concept of dispersive concentration, or spectral split concentration, has been explored for decades. But the typical application uses a separate solar cell for each wavelength band.

With the new materials, Ning said he hopes to build a monolithic lateral super-cell that contains multiple subcells in parallel, each optimized for a given wavelength band. The multiple subcells can absorb the entire solar spectrum. Such solar cells will be able to achieve extremely high efficiency with low fabrication cost. The team is working on both

the design and fabrication of such solar cells.

Similarly, the new quaternary alloy nanowires with large wavelength span can be explored for color-engineered light applications.

The researchers have demonstrated that color control through alloy composition control can be extended to two spatial dimensions, a step closer to color design for direct white light generation or for color displays.

The team’s research was initially supported by Science Foundation Arizona and by the U.S. Army Research Office. For more information, see the research group’s Web site at http:// nanophotonics.asu.edu

Chevron Tests Emerging Solar Technologies in Central California

2010-03-22

Former Bakersfield Refinery Converted to Next- Generation Solar Demonstration Facility

Chevron Corporation (NYSE: CVX) today announced the start of Project Brightfield, a demonstration of next-generation solar energy technologies in Bakersfield, California. The project, created on the site of a former Chevron refinery, will evaluate seven emerging photovoltaic technologies to help determine the potential application of renewable power at other company-owned facilities.

The former refinery site has been repurposed to test the performance of six emerging thin-film technologies and one emerging crystalline- silicon photovoltaic technology, which were provided by independent solar companies. Chevron Tests Solar Technologies

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