Control of Nanowire Growth Advances Silicon Photonics

Researchers from the Swiss Federal Institute of Technology Lausanne (EPFL) Laboratory of Semiconductor Materials, together with colleagues from the Massachusetts Institute of Technology (MIT) and the Ioffe Institute in Russia, have discovered a way to grow nanowire networks in a highly controlled and fully reproducible manner. First, they needed to understand what happens at the onset of nanowire growth — a process, they found, that goes against currently accepted theories.

EPFL researchers have found a way to control and standardize the production of nanowires on silicon surfaces. This discovery could make it possible to grow nanowires on electronic platforms, with potential applications including the integration of nanolasers into electronic chips and improved energy conversion in solar panels. Courtesy of Jamani Caillet/EPFL.

The standard process for producing nanowires is to make tiny holes in silicon monoxide and fill them with a nanodrop of liquid gallium. Research aimed at controlling this process has tended to focus on the diameter of the hole, but this approach has not paid off, said the researchers.

The researchers found that, contrary to common understanding, vertical growth of nanowires starts at the oxide-substrate line interface. They showed that by altering the diameter-to-height ratio of the hole, they could fully control how the nanowires grew. At the correct ratio, the liquid gallium will solidify in a ring around the edge of the hole, which will prevent the nanowires from growing at a nonperpendicular angle. The researchers say that this process should work for all types of nanowires.

Two different configurations of the droplet within the opening: above, hole fully filled and partially filled and, below, illustration of GaAs crystals forming a full ring or a step underneath the large and small gallium droplets. Courtesy of EPFL.

This new production technique could help advance nanowire research. Nanowires can alter how electricity or light passes through them, and could be used to add optical functionalities to electronic chips, making it possible to generate lasers directly on silicon chips and to integrate single-photon emitters onto chips for coding purposes. They could potentially be applied in solar panels to improve how sunlight is converted into electrical energy.

Further samples should soon be developed, the team said. “We think that this discovery will make it possible to realistically integrate a series of nanowires on silicon substrates,” said professor Anna Fontcuberta i Morral. “Up to now, these nanowires had to be grown individually, and the process couldn’t be reproduced.”

The research was published in Nature Communications (https://doi.org/10.1038/s41467-019-08807-9).