Manufacturing Bits: March 13

Gallium oxide substrates
Kyma Technologies has rolled out a substrate line based on crystalline beta-phase gallium oxide (β-Ga2O3) materials.

Single crystal gallium oxide (ß-Ga2O3) substrates (Source: Kyma)

Crystalline beta gallium oxide is a promising wide bandgap semiconductor material. It has a large bandgap of 4.8 – 4.9 eV with a high breakdown field of 8 MV/cm. The technology has a high voltage Baliga figure of merit (HV-BFOM), which is more than 3,000 times greater than silicon, more than 8 times greater than silicon carbide (SiC) and more than 4 times greater than that of gallium nitride (GaN)

Kyma’s β-Ga2O3 substrates are produced by slicing bulk crystals. Then, they lap and polish them using a chemical-mechanical-polishing (CMP) process. This in turn creates an epi-ready substrate. This new offering was made possible by Kyma’s collaboration with Northrop-Grumman Synoptics.

Flat gallium
Rice University and the Indian Institute of Science have developed a way to make atomically-thin flat gallium.

Researchers have produced a two-dimensional (2D) version of gallium called gallenene. Gallenene, a thin film of conductive material, could be used to make metallic contacts in 2D devices. Gallenene is to gallium what graphene is to carbon, according to researchers.

Gallium, which is a metal, has a low melting point. Unlike other 2D structures, gallium can’t be grown using traditional vapor phase deposition methods.

In the lab, Rice and the Indian Institute of Science heated bulk gallium just below its melting point at 29.7 degrees Celsius. This, in turn, caused gallium to drip onto a glass slide, thereby forming the equivalent of gallenene. Then, the material was cooled. In the lab, researchers produced gallenene sheets on a silicon substrate.

A model of the structure of gallenene is shown after exfoliation from bulk gallium. (Courtesy of the Ajayan Research Group)

They also exfoliated gallenene on other substrates, such as gallium nitride, gallium arsenide, silicone and nickel. “The current work utilizes the weak interfaces of solids and liquids to separate thin 2D sheets of gallium,” said Chandra Sekhar Tiwary, an assistant professor at the Indian Institute of Technology. “The same method can be explored for other metals and compounds with low melting points.”

Pulickel Ajayan, a professor at Rice, added: “Near 2-D metals are difficult to extract, since these are mostly high-strength, nonlayered structures, so gallenene is an exception that could bridge the need for metals in the 2-D world.”

2D material bonanza
2D materials are gaining steam in the R&D labs. The 2D materials could enable a new class of field-effect transistors (FETs), but the technology isn’t expected to appear until sometime in the next decade.

In 2004, graphene was the first 2D material isolated. Other 2D materials include boron nitride and the transition-metal dichalcogenides (TMDs). One TMD, molybdenum diselenide (MoS2), is gaining interest in the market.

The problem? Only a few dozen 2D materials have been synthesized, according to École Polytechnique Fédérale de Lausanne (EPFL).

Now, using a screening algorithm, EPFL and NCCR MARVEL have identified more than 1,000 new 2D materials with promising properties. Initially, researchers analyzed the structure of more than 100,000 3D materials. Then, they narrowed down the candidates using a digital exfoliation process. From there, researchers identified 5,600 materials with 2D properties.

Then, researchers singled out 1,800 structures that could be exfoliated. Of those, 1,036 were easy to exfoliate. “Our study demonstrates that digital techniques can really boost discoveries of new materials,” said Nicola Marzari, the director of NCCR MARVEL. “In the past, chemists had to start from scratch and just keep trying different things, which required hours of lab work and a certain amount of luck. With our approach, we can avoid this long, frustrating process because we have a tool that can single out the materials that are worth studying further, allowing us to conduct more focused research.”