Researchers in the United States have synthesized a new silicon material with direct band gap allotropes. It combines the absorptive capacity of gallium arsenide and the processing advantages of traditional silicon materials, which may revolutionize solar cells and lighting equipment. The current synthesis process is long and expensive, but researchers believe that this technology can solve this problem.
Silicon material is a pillar of the electronics industry, but the usual diamond cubic structure allotropes have indirect band gaps. This means that electrons cannot cross back and forth between the valence band and the conduction band by absorbing or emitting photons. They also need phonons to save power. This reduces the absorption of silicon material and the efficiency of light emission. Silicon solar cells require thick silicon wafers to absorb enough light, while LEDs require more expensive materials such as gallium arsenide, which are toxic and easily decompose.
The tetrahedral bond structure of silicon promotes it to have a variety of hypothetical metastable structures, many of which have a slightly higher energy than the ground state. In a high pressure environment, multiple structures can be observed, four of which are dynamically stable under ambient conditions. In 2013, Timothy Strobel of Washington Carnegie Research and his colleagues discovered Na4Si24. Now, they found that by heating Na4Si24 to 400K under vacuum and gradually driving away the sodium atoms, a new silicon structure of orthorhombic allotropes was obtained. Theoretical calculations and experiments show that the material is stable at 750K and 10GPa, and has a direct band gap of about 1.3eV, which is an ideal material for photovoltaic cells.
The material currently only produces powder samples, and its complicated manufacturing process obviously limits its industrial applications. However, Strobel is optimistic that these difficulties can be overcome. He said that now we are focusing on methods that can form excellent performance single crystal materials. Once we can do it, we can really confirm whether the material can bring about revolutionary development of semiconductor technology. In addition, if we can obtain a substrate of reasonable size for this crystal, we can produce this allotrope at any high pressure, and we can also produce multi-size epitaxially grown crystals currently produced using diamond.
George Nolas, a physicist at the University of South Florida, believes that the most significant point of this article is its new synthesis method. He said that this method may be used for the synthesis of other open frame material structures. Artem Oganov, an electronic structural theorist at the State University of New York at Stony Brook, also praised this complex method for preparing materials. “The question now is: Is this material capable of defeating silicon?†he said. “If not, then this is a good attempt. These repeated attempts should be justified. If so, then we can celebrate with champagne! â€
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