Novel Semiconductor Has Double-Helix Structure of DNA

An inorganic semiconductor has excellent electronic properties and flexibility, all thanks to a double-helix structure

On the left side crystals of residual black phosphorus and tiniodide. The material is easy to produce and shows extraordinary optical and electronic properties, as well as extreme mechanical flexibility.
Photo: Andreas Battenberg/TUM
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The use of DNA in nanodevices has in large part been aimed at manipulating DNA to act like a semiconductor. But what if we could create an inorganic semiconductor that had some of the properties, including flexibility, of DNA?

The world of electronics is going to find out soon. Researchers at the Technical University of Munich (TUM) have discovered a double helix structure similar to DNA’s in an inorganic semiconductor material. The material consists of tin (Sn), iodine (I) and phosphorus (P), resulting in its chemical name SnIP. These three elements form in the SnIP around a double-helix configuration.

In research described in the journal Advanced Materials, the TUM researchers found that that arrangement of atoms into a double-helix structure in the centimeter-long fibers enabled the material to be split into smaller strands. In the lab, the TUM researchers were able to make fibers as small as five double helix strands that were only a few nanometers thick. The researchers believe that being able to get the fibers down to this size promises a host of nanoelectronic applications.

Of course, being a semiconductor means that SnIP has an inherent band gap. But unlike other inorganic semiconductors it is extremely flexible—another property that stems from its double-helix structure.

"Especially the combination of interesting semiconductor properties and mechanical flexibility gives us great optimism regarding possible applications," said Tom Nilges, a professor at TUM, whose lab conducted the research, in a press release. "Compared to organic solar cells, we hope to achieve significantly higher stability from the inorganic materials. For example, SnIP remains stable up to around 500°C (930 °F)."

A major breakthrough is the ability to scale up the production of a double helix material beyond the milligram scale.

“This is the first double-helix material, to my knowledge, to be prepared on a gram scale,” said Nilges in an e-mail interview with IEEE Spectrum. “We can prepare it on a gram scale in a simple solid phase reaction via the gas phase. Solid phase preparations are not unknown in industry therefore I am quite sure that a company can upscale such a material.”

“The preparation of SnIP is easy and non-toxic components are involved,” said Nilges. “All elements in SnIP are abundant and better available than Gallium (Ga), Indium (In) or Arsenide (As).” Indium phosphide (InP) and gallium arsenide (GaAs)  are prominent semiconductors used in today’s computer chips that contain such toxic or expensive elements.

The production process is a straightforward synthesis with a pure material at the end of the line, according to Nilges, who points out that this stands in contrast to carbon nanotubes that are not easily available in phase-pure form.

The TUM researchers have applied for a patent on the synthesis and possible applications of SnIP, including flexible semiconductor devices, solar cells, thermoelectric devices and water splitting.

Nilges added: “Once we find a company who is interested in this material, a realization of devices is possible. A realistic timeline for lab-based devices is probably 1-2 years. At the moment, we are looking for interested companies. Probably a realistic timeline is shortened once industry becomes involved.”

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