Alta Devices moves out of the lab and into the valley
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BEYOND THE LAB
Alta Devices moves out of the lab and into the valley Jessica M. Smith
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n the world of technology start-ups, especially clean energy, “the valley”—also known as “the valley of death”—refers to the gap in capital between the funding of invention—through government grants and venture capital— and mass production. Recently, the thinfilm solar-cell manufacturer Solyndra famously failed to cross this valley, declaring bankruptcy after accepting millions of dollars in US government gap funding. The controversy around this particular case, and around the fate of many solar start-ups generally, means that all eyes are on Alta Devices. As the start-up begins production on its pilot line, the clean energy community will watch as Alta Devices attempts to take its technology out of the lab and into the valley. Alta Devices was founded by Harry Atwater of the California Institute of Technology and Eli Yablonovic of the University of California–Berkeley in collaboration with venture capitalist Andy Rappaport. The company relies on Yablonovic’s research in the 1980s on a technique called epitaxial liftoff. The active layer Alta Devices uses in solar cells, gallium arsenide (GaAs), can be produced inexpensively using this technique without degrading the performance of the cell. The team began the company in 2007, and has subsequently worked toward perfecting epitaxial liftoff of GaAs at a laboratory scale. When the pilot production line opens later this year, this invention will be produced for the first time on large scale. Epitaxial liftoff is an efficient way to create thin wafers of GaAs. On top of a high-purity GaAs surface, layers of GaAs are deposited with alternating layers of aluminum arsenide (AlAs). “We take advantage of the serendipitous fact
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that the etch selectivity between AlAs and GaAs is more than 100 million, so that it’s possible to immerse the structure in an etching solution and remove the AlAs layer completely without etching the GaAs layer,” said Atwater. The free GaAs wafers are of very high purity, and the original GaAs surface can be used again to create more wafers. Solar cells made from these GaAs wafers compare favorably to conventional silicon photovoltaic (PV) cells. The highest performing silicon PV cells are made out of high-purity silicon, similar to that found in computer chips, which allows them to reach solar conversion efficiencies near 30%. The silicon used in these cells, however, is costly to produce, and the cells require a thick layer in order to reach maximum efficiency.
Gallium arsenide PV cells made through epitaxial liftoff can also reach high efficiency—currently 23.4% and climbing. Because of the properties of GaAs, efficient solar cells can be made with a much thinner layer of material. Combined with the less expensive processing method, Alta Devices' solar cells can be made for a fraction of the cost of silicon PV cells. The conventional wisdom of the photovoltaics community is that any solar cell that is in
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