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Liquid metal solidifies new method for growing semiconductors

eGaIn enables easy electrochemical route to high-quality germanium films

by Matt Davenport
June 5, 2017 | A version of this story appeared in Volume 95, Issue 23

A photo shows what the germanium semiconductor film looks like to the naked eye—basically a dull, gray splotch. Next to it, a colorized micrograph reveals the distribution of elements and shows a high-quality germanium film.
Credit: J. Am. Chem. Soc.
A new electrochemical process puts semiconductors at researchers’ fingertips (left). The process creates germanium thin films (green) on silicon (orange) with specks of gallium (white), as shown by electron microscopy and X-ray analysis (right).

Growing high-quality semiconducting crystals isn’t easy. It typically takes high temperatures, highly reactive precursors, and extensive equipment. Electrochemical deposition could simplify the process, but attempts using conventional solvents yield “amorphous junk,” says Stephen Maldonado of the University of Michigan. Working with colleagues at Ohio State University, Maldonado’s team has found that a liquid metal can help electrochemistry conquer this shortcoming (J. Am. Chem. Soc. 2017, DOI: 10.1021/jacs.7b01968). The researchers started with an aqueous germanium oxide solution and introduced eutectic gallium-indium, or eGaIn. This liquid metal forms an intermediate layer between the solution and a solid silicon substrate. Germanium reduced in water can cross the interface into the eGaIn and migrate to the silicon. By tuning the thickness of the eGaIn layer, the researchers ensure that germanium accumulates into a high-quality, crystalline film. This low-cost, benchtop approach works at room temperature, unlike conventional semiconductor growth, Maldonado says. The group is exploring liquid metal solvents further, hoping to inspire others to rethink how they make semiconductor circuits and devices.


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