University of Illinois researchers say they’ve developed a technique that could help engineers build high-performance solar cells and other electronics using tiny semiconductors called “nanowires.” Nanowires have been seen as a promising technology for improving the performance and efficiency of devices from solar cells to lasers. However, engineers have had trouble using semiconductors in this class because they do not easily integrate with silicon, the most common platform for integrating semiconductors in manufacturing.
The problem is a mismatch in the the specific distances between the atoms in the materials’ crystal structure (also known as the “lattice constant”). Because the materials have different lattice constants, “they cannot be stacked on top of each other in a straightforward way without generating dislocations,” said electrical and computer engineering professor Xiuling Li. In the past, engineers have dealt with this mismatch by covering silicon wafers with a thin film of semiconductor material. But the mismatch in the crystal lattices of the materials can cause strain, and degrade the performance of a solar cell over time. Instead of a thin film, the Illinois team grew a densely packed array of indium gallium arsenide “nanowires”, tiny strands of semiconductor that grow up vertically from the silicon wafer.
By “dissipating the mismatch strain energy laterally through the sidewalls,” Li explained, the nanowires offer engineers freedom from lattice-matching restrictions. Nanowires can also improve light absorption, enhancing solar cell performance and efficiency, and reduce the cost of solar cells by using less material than thin films. Next, Li and her group hope to develop multi-junction solar cells using nanowires.
The research was supported by the U.S. Department of Energy and the National Science Foundation. The paper, “InxGa1-xAs Nanowires on Silicon: One-Dimensional Heterogeneous Epitaxy, Bandgap Engineering, and Photovoltaics,” was published in the journal Nano Letters.
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