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Patented process could build better SiC devices

Off-axis substrates use layers to minimise potential defects

Research by Jim Edgar, professor of chemical engineering at Kansas State University, could result in better SiC carbide devices. Edgar has received a patent for his invention 'Off-axis silicon carbide substrates', which uses layers to minimise potential defects.

"It's like a stacked cake separated by layers of icing," Edgar said. "When the layers of semiconductors don't match up very well, it introduces defects. Any time there is a defect, it degrades the efficiency of the device."

His patent (number 8823014) describes a method of epitaxial growth of a material on a crystalline substrate that includes selecting a substrate having a crystal plane that includes a number of terraces with step risers that join adjacent terraces.

Each terrace presents a lattice constant that substantially matches a lattice constant of the material, and each step riser presents a step height and offset that is consistent with portions of the material nucleating on adjacent terraces being in substantial crystalline match at the step riser.

The method also includes preparing a substrate by exposing the crystal plane; and epitaxially growing the material on the substrate such that the portions of the material nucleating on adjacent terraces merge into a single crystal lattice without defects at the step risers.

Edgar describes the research discovery as serendipitous. Several years ago, when Yi Zhang, a 2011 doctoral graduate in chemical engineering, was working in the laboratory, she found a substrate sample that was very smooth.

Collaborative researchers at the State University of New York at Stony Brook and the University of Bristol in the UK later confirmed the layer's presence and proved that it had fewer defects than on the standard substrate.

"We have applied this process to other systems," Edgar said. "We are working on verifying that it is not just these specific materials we started with, but that it can be applied to a lot of different materials."

Some of Edgar's latest research focuses on two different boron compounds: boron phosphide and icosahedral phosphide.

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