The University of Illinois claims to have developed a lower-cost method of manufacturing compound semiconductors such as GaAs for many electronic device applications, including solar cells.
Gallium arsenide (GaAs) and related compounds claim to offer nearly twice the efficiency as silicon in solar cells. But solar cells based on these materials are expensive to make.
'If you grow 10 layers in one growth, you only have to load the wafer one time,' said Li, a professor of electrical and computer engineering. 'If you do this in 10 growths, loading and unloading with temperature ramp-up and ramp-down take a lot of time. If you consider what is required for each growth - the machine, the preparation, the time, the people - the overhead saving our approach offers is a significant cost reduction.'
In a paper to be published online May 20 in the journal Nature, the group describes its methods and demonstrates three types of devices using gallium arsenide chips manufactured in multilayer stacks: light sensors, high-speed transistors and solar cells. The authors also provide a detailed cost comparison.
Another advantage of the multilayer technique is the release from area constraints, especially important for solar cells. As the layers are removed from the stack, they can be laid out side-by-side on another substrate to produce a much larger surface area, whereas the typical single-layer process limits area to the size of the wafer.
The group deposited multiple layers of the material on a single wafer, creating a layered, “pancake” stack of gallium arsenide thin films.
''Next the researchers individually peel off the layers and transfer them. To accomplish this, the stacks alternate layers of aluminum arsenide with the gallium arsenide. Bathing the stacks in a solution of acid and an oxidizing agent dissolves the layers of aluminum arsenide, freeing the individual thin sheets of gallium arsenide,'' according to the group.
The paper’s co-authors include two scientists from Semprius Inc., a North Carolina-based startup company that is beginning to use this technique to manufacture solar cells.
Semprius is developing concentrator photovoltaic (CPV) modules for large-scale solar power generation. Semprius' micro-transfer printing technology enables CPV modules constructed from a large array of very small gallium arsenide-based, multi-junction solar cells. Module cost is minimized by using high concentration ratio.
Journal Nature - GaAs photovoltaics and optoelectronics using releasable multilayer epitaxial assemblies
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