A technology has been developed to insert a graphene film between a wafer and a semiconductor material, allowing only the semiconductor material to be removed and the wafer to be reused. Expectations are high that this will enable mass production of high-quality semiconductor materials at very low prices in the future.

Professor Lee Dong-seon's team from the Department of Electrical, Electronic and Computer Engineering at GIST (Gwangju Institute of Science and Technology, President Lim Ki-chul) announced on the 19th that they have developed a 'gallium nitride remote epitaxy' technology using only the metal organic chemical vapor deposition method through joint research with the Massachusetts Institute of Technology (MIT) in the United States.

This technology allows gallium nitride semiconductors to be grown on a wafer and then easily removed, allowing continuous production of semiconductors as if copying them from a single wafer.

The structure of a semiconductor is largely composed of a wafer and semiconductor materials. Just as a building can be built on a foundation (wafer) when constructing a building, wafers made of silicon, silicon carbide, sapphire, etc. are essential for growing high-quality semiconductor materials. Semiconductor materials are made by epitaxy, a technique that grows a thin film of the same or similar material on top of the wafer in a very well-aligned shape.

However, with the existing epitaxy technology, a wafer that is approximately 1 mm thick, which is about a thousand times thicker, was required to obtain a semiconductor material that is approximately 1 μm (micrometer) thick, and it was very difficult in terms of technology and cost to extract and use only the semiconductor material that was actually used.

The 'remote epitaxy' technology, first proposed by Professor Ji-Hwan Kim of MIT in 2017, is a unique technology that places a very thin two-dimensional material, such as graphene, on a wafer and grows a semiconductor material on top of it. Not only can it obtain a high-quality semiconductor material in the form of a thin film that 'copy' the characteristics of the wafer, but it can also be 'peeled' from the wafer, so theoretically the wafer can be reused infinitely.

This technology is based on the principle that the electrical properties of the wafer surface penetrate the graphene film, so that only the semiconductor material can be peeled off because the semiconductor material is not directly bonded to the wafer. It is similar to the phenomenon where, when you place paper (graphene film) on top of a bar magnet (wafer) and sprinkle iron powder (semiconductor material), the iron powder gathers at the anode with the paper in between without directly sticking to the bar magnet.

In particular, gallium nitride semiconductors, which are widely used in LED displays and electric vehicle charging devices, require gallium nitride wafers for maximum efficiency. However, since gallium nitride wafers are about 100 times more expensive than sapphire wafers, sapphire wafers, which have a crystallinity of only one thousandth of that, have been used. Accordingly, great expectations were raised for remote epitaxy technology that could reuse expensive gallium nitride wafers.

On the other hand, it was judged that remote epitaxy technology would not be applicable under high-temperature growth conditions such as the 'metal organic chemical vapor deposition' method mainly used in the industry because the surface of the gallium nitride wafer would decompose and the graphene film would be damaged.

By introducing 'aluminum nitride (AlN)' wafers with similar properties to gallium nitride, the research team succeeded in implementing remote epitaxy technology that grows and peels off gallium nitride thin films using only the 'metal organic chemical vapor deposition' method.

This study opens the way to the production of highly crystalline and expensive gallium nitride semiconductors in industrial settings using remote epitaxy technology. If applied to actual semiconductor production, it will be possible to mass-produce high-quality semiconductor materials at very low prices. Furthermore, since only semiconductors grown in the form of a thin film can be separated and used, it has become possible to stack various semiconductors with different functions in the same narrow space.

In addition, the 'non-peeling mechanism' was also discovered, in which the graphene film is damaged when there are nano-sized scratches on the aluminum nitride surface, making it impossible to separate the gallium nitride semiconductor from the wafer.

Previously, there were frequent studies that only 'copied' semiconductor materials by imitating remote epitaxy technology and did not reveal whether 'peeling' occurred, but this study clearly presented for the first time that 'peeling' is an essential condition in remote epitaxy technology.

Professor JIST Dong-seon Lee said, “With this research result, we were able to present a method and essential conditions for implementing the ‘gallium nitride remote epitaxy’ technology that enables peeling,” and added, “We will develop semiconductor super-gap technologies such as remote epitaxy technology through continuous research exchanges with MIT.”

Since 2019, the professor has been conducting joint research with Professor Ji-Hwan Kim of MIT and has been accelerating the acquisition of next-generation semiconductor technology that will lead the global market.

This research, supervised by Professor Lee and conducted jointly with MIT by PhD student Kwak Hee-min, was supported by the Nano and Materials Technology Development Project and the Individual Research Project (Mid-career Researcher) of the National Research Foundation of Korea through the Ministry of Science and ICT, and was published on June 6 in 'ACS Nano,' a renowned international academic journal in the field of materials science and chemistry.