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Ground-breaking research produces record levels of strain in single-crystal silicon

Researchers at the University of Surrey, with support from NPL and the Surrey Ion Beam Centre, developed a single-step procedure to put single-crystal silicon under more strain than has been achieved before

The discovery could be crucial to the future development of silicon photonics, which underpins the technologies behind the internet-of-things, and is currently constrained by the lack of cheap, efficient, and easily integrated optical emitters.

The new approach is also an important step towards creating near-infrared sensors that could pave the way towards developing more sophisticated smartphones, such as fitting them with carbon monoxide sensors.

A new paper published in the Physical Review Materials journal describes how the team applied strain to silicon membranes using ion implantation, in a similar manner to tightening a drum skin. Strain enhances the ability of silicon to emit light by changing its electronic structure.

Vivian Tong, Higher Research Scientist at NPL, was involved in the consortium and used a scanning electron microscope technique called electron backscatter diffraction (EBSD) to measure the shape and structure of the strained membranes.

This consists of firing electrons at the silicon membrane and taking pictures of how the electrons bounce (‘backscatter’) off the membrane using a camera on the side of the electron microscope. The electrons bounce off the membrane in different formations (‘diffraction patterns’) depending on the shape of the membrane and the distortion in the silicon crystal.

For this project, Vivian used EBSD to measure the shape of the strained membrane, and to check that the high strains were applied uniformly to the membrane and didn’t create unexpected defects in the material.

Now the team are transferring the same procedure to germanium. If successful, they will open the door to creating germanium lasers, which are compatible with silicon-based computers, and could revolutionise communications systems by means of new opto-electronic devices. In the second phase of this research, Vivian will be undertaking further EBSD measurements on the new samples, to try and measure the strain applied to the membrane.

Vivian Tong, Higher Research Scientist, NPL said: “The most exciting aspect of this method is that it is conceptually simple and fast to implement, and therefore readily scalable to manufacturing real devices. I look forward to working with Surrey to verify, refine and extend the technology, including making further use of NPL’s broad range of measurement capability.”


09 Feb 2022