Next to silicon, germanium (Ge) is the most widely used semiconductor material in the world. But while it’s great at conducting electricity, its inefficiency at turning light into electricity (or electricity into light) restricts the other applications for which it can be used.
Paul Simmonds, an assistant professor with a dual appointment to the departments of physics, and materials science and engineering, wondered if there was a way to fine-tune germanium’s physical properties, and thus improve its optoelectronic characteristics (how well it interfaces between electronics and light).
The Air Force Office of Scientific Research also was intrigued and funded a proposal titled “Optoelectronic Properties of Strain-Engineered Germanium Dots” with a three-year, $622,000 grant. Simmonds is working on the project through a sub-award administered through the University of California, Merced, and the University of California, Los Angeles. Boise State’s share of the award is $206,000.
“If we can turn Ge into an optoelectronic material, then other characteristics would make it attractive as a laser material,” Simmonds said. “It’s a bit like alchemy. We hope to change the fundamental properties of an element on the periodic table simply by stretching it a little.”
For years, scientists have tried putting germanium under tensile strain (stretching it at the atomic level) in order to improve its optoelectronic properties. But germanium is fragile, and crystalline imperfections cause it to break before enough tensile strain can be built up.
Simmonds and his research team have responded to the challenge by developing a new family of self-assembled nanomaterials capable of storing large amounts of tensile strain, without damage to the crystalline structure.
“Self-assembly has allowed us to develop a way for the materials to sustain high tensile strains without falling apart,” Simmonds said. “Instead of remaining flat, the atoms rearrange to form nanoscopic islands, like raindrops on the top of a car but about a million times smaller. The process of rearranging into 3D islands relieves a little of the strain and creates a window that allows us to have high tensile strain without breaking any atomic bonds. We’ve shown this works with other materials and now we want to try it with germanium.”
Doing so would help establish tensile self-assembly as a novel means by which to integrate dissimilar materials and demonstrate to the research community that nanostructure band engineering with tensile strain is an effective tool for discovering and designing materials for technological innovation.
While their work has real-world applications — creating direct band gap Ge nanostructures would be a critical breakthrough in optoelectronic materials research — Simmonds is excited that it’s also an opportunity to simply understand the world a little better.
An international team of scientists constructs the first germanium-tin semiconductor laser for silicon chips
Scientists from Forschungszentrum Jülich and the Paul Scherrer Institute in Switzerland in cooperation with international partners have presented the first semiconductor consisting solely of elements of main group IV. As a consequence, the germanium-tin (GeSn) laser can be applied directly onto a silicon chip and thus creates a new basis for transmitting data on computer chips via light: this transfer is faster than is possible with copper wires and requires only a fraction of the energy. The results have been published in the journal Nature Photonics.
The transfer of data between multiple cores as well as between logic elements and memory cells is regarded as a bottleneck in the fast-developing computer technology. Data transmission via light could be the answer to the call for a faster and more energy efficient data flow on computer chips as well as between different board components. “Signal transmission via copper wires limits the development of larger and faster computers due to the thermal load and the limited bandwidth of copper wires. The clock signal alone synchronizing the circuits uses up to 30% of the energy – energy which can be saved through optical transmission,” explains Prof. Detlev Grützmacher, Director at Jülich’s Peter Grünberg Institute.
Some long-distance telecommunication networks and computing centres have been making use of optical connections for decades. They allow very high bandwidths even over long distances. Through optical fibres, signal propagation is almost lossless and possible across various wavelengths simultaneously: a speed advantage which increasingly benefits both micro- and nanoelectronics. “The integration of optical components is already well advanced in many areas. However, in spite of intensive research, a laser source that is compatible with the manufacturing of chips is not yet achievable,” according to the head of Semiconductor Nanoelectronics (PGI-9).