Midea develops thin film semiconductors with a single atomic diameter
Researchers at North Carolina State University in the United States said today that they have developed new technologies for manufacturing high-quality atomic-scale semiconductor films (thickness is only one atomic diameter). Professor Cao Linyou, an assistant professor of materials science and engineering, said that new technologies can reduce the size of existing semiconductor technologies to the atomic level, including lasers, light-emitting diodes, and computer chips.
The material the researchers studied was molybdenum sulfide, an inexpensive semiconductor material with similar electronic and optical properties to those used in the semiconductor industry today. However, molybdenum sulfide is different from other semiconductor materials because it can grow monolayers to form a monolayer film without losing the original material properties.
In the new technology, researchers placed sulfur powder and molybdenum chloride powder in a furnace and gradually raised the temperature to 850 degrees Celsius. At this time, the two powders evaporated (vaporized) and chemically reacted to form molybdenum sulfide. Continue to maintain high temperatures, molybdenum sulfide can be deposited on the substrate to form a thin film of molybdenum sulfide.
Cao Linyou said that the key to their success is to find a new molybdenum sulfide growth mechanism, that is, self-limiting growth, and precisely control the thickness of the molybdenum sulfide layer by controlling the partial pressure and vapor pressure in the high-temperature furnace.
Partial pressure represents the tendency of atoms or molecules suspended in the air to accumulate as solids precipitate onto the substrate; vapor pressure represents the tendency of solid atoms or molecules on the substrate to vaporize into the air. To obtain a single layer of molybdenum sulfide on the substrate, the partial pressure must be higher than the vapor pressure; the higher the partial pressure, the more molybdenum sulfide layer deposited on the bottom. If the partial pressure is higher than the vapor pressure of the monolayer film formed on the substrate, but lower than the vapor pressure of the bilayer film, the balance between the partial pressure and the vapor pressure can ensure the formation of a single layer of molybdenum sulfide film. After the film growth stops automatically, it no longer develops to multiple layers. This is "self-limiting growth of the film."
Partial pressure is controlled by adjusting the amount of molybdenum chloride in the high-temperature furnace. The greater the amount of molybdenum in the furnace, the higher the partial pressure. Cao Linyou said that with this technology, they each obtained a single-layer thin film of molybdenum sulphide with a wafer size and atomic diameter. At the same time, it is also possible to obtain 2-4 molybdenum sulfide thin films by changing the partial pressure.
Researchers are currently trying to find other ways to make similar films that each consist of different materials. At the same time, they are also using new technologies to produce field-effect transistors and light-emitting diodes. (Reporter Mao Li)
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