Researchers cheaply produce thin films of the semiconductor gallium arsenide

Faster flexible electronics and more efficient solar cells are the promise of gallium arsenide as researchers at Massachusetts Institute of Technology (MIT) begin to work on photovoltaic devices using their cheaper graphene production process.

Gallium arsenide is a better material than silicon, electrons move five times faster through it and it is less sensitive to ambient temperature than silicon. But microchips and solar cells are made from silicon because it is an abundant element and the manufacturing processes to make electronics and photovoltaics from it have been cheaper than gallium arsenide’s. That could now all change as MIT researchers have found a way to essentially photocopy a solar cell or microchip design onto gallium arsenide using graphene.

“We can apply this technique to materials like gallium arsenide or gallium nitride,” says Sang-Hoon Bae, a postdoctoral associate in MIT’s department of mechanical engineering. “We are working on the solar cell. Gallium arsenide is a good candidate for a solar cell. In our approach we can copy and paste the gallium arsenide freestanding film, so we can expect to get the [manufacturing] costs down.”

Massachusetts Institute of Technology researchers have devised a way to grow a single crystalline compound semiconductor on its substrate through two-dimensional materials. The compound semiconductor thin film is then exfoliated by a flexible substrate, showing the rainbow colour that comes from thin film interference. Credit: MIT / Wei Kong and Kuan Qiao

The photocopy-style production process involves a gallium arsenide wafer and a layer of graphene applied to it. Gallium and arsenide are then poured over the graphene which covers the gallium arsenide wafer. The gallium and arsenide atoms then arrange themselves to form a copy of the underlying gallium arsenide wafer. This copy layer, which can be tens to hundreds of nanometres thick, can then be peeled off the graphene producing a thin film replica of the wafer. This technique is called, remote epitaxy. Epitaxy is the name for the growth of crystals.

This technique allows for the rapid production of thin films of gallium arsenide using one wafer, a far cheaper manufacturing approach. “Not only gallium arsenide and gallium nitride, this is a general approach and we can play with other materials,” Bae added. Lithium fluoride is another material that is being examined for this process. Because the process produces thin films these can be used to build up conformable multifunctional devices, such as flexible solar cells, which Bae’s team is working on, or wearable sensors. The researchers have even proposed mobile phones that attach to the skin.

The researchers think the process works like two magnets interacting through a piece of paper. The gallium has a negative charge while arsenic has a positive one. This difference means their atoms interact through the graphene and subsequently arrange themselves in parallel, as a copy, to the wafer’s gallium arsenide crystalline structure.

Bae’s team collaborated with researchers from Sun Yat-Sen University, the University of Virginia, the University of Texas at Dallas, the United States (US) Naval Research Laboratory, Ohio State University, and Georgia Institute of Technology. The research was supported in part by the Defense Advanced Research Projects Agency, the US Department of Energy, the US Air Force Research Laboratory, LG Electronics, Amore Pacific, LAM Research, and Analog Devices.

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