Blog

Jun 14, 2023

Germanium

Researchers from multiple research institutes have demonstrated electrons and

Researchers from multiple research institutes have demonstrated electrons and holes can move faster in specific germanium-tin alloys than in either silicon or germanium. The research was done to enhance vertically-oriented transistors and shows circuits with lower operating voltages and much smaller footprints than equivalent planar circuits.

Researchers at ForschungsZentrum Jülich, Germany; the University of Leeds, UK; IHP- Innovations for High Performance Microelectronics, Frankfurt (Oder), Germany, and RWTH Aachen University, Germany, contributed to a paper published in Nature Communications Engineering, entitled Vertical GeSn Nanowire MOSFETs for CMOS Beyond Silicon.

They reported that germanium–tin transistors exhibit an electron mobility that is 2.5 times higher than a comparable transistor made of pure germanium. And because germanium and tin are both in Group IV of the periodic table, the same group as silicon, these transistors could be integrated directly into conventional silicon chips with existing production lines.

The paper notes that "GeSn alloys offer a tunable energy bandgap by varying the Sn content and adjustable band off-sets in epitaxial heterostructures with Ge and SiGe. In fact, a recent report has shown that the use of 8 percent tin alloyed with 92 percent germanium as source on top of Ge nanowires enhances the p-MOSFET performances."

One of the major aspects of the paper was the development of the epitaxial growth to produce the GeSn binaries in a vertical structure. The paper reports on top-down fabricated vertical GeSn-based gate-all-around nanowire MOSFETs with nanowire diameters down to 25 nm. Two epitaxial heterostructures, GeSn/Ge/Si and Ge/GeSn/Ge/Si, are designed to facilitate the co-optimization of p- and n-type transistors, respectively. As a result full CMOS functionality is demonstrated with a CMOS inverter. In addition the n-type GeSn devices show switching properties at low temperatures to meet the requirements of cryogenic quantum computing.

"In addition to their unprecedented electro-optical properties, a major advantage of GeSn binaries is also that they can be grown in the same epitaxy reactors as Si and SiGe alloys, enabling an all-group IV optoelectronic semiconductor platform that can be monolithically integrated on Si," the paper reports.

"The collaboration demonstrated the potential of low-bandgap GeSn for advanced transistors with interesting electrical properties, such as high carrier mobilities in the channel, low operating voltages and a smaller footprint," said CEA Fellow Jean-Michel Hartmann, a co-author of the paper. "Industrialization is still far away. We are advancing on the state of the art and showing the potential of germanium tin as a channel material."

Vertical GeSn Nanowire MOSFETs for CMOS Beyond Silicon

www.cea.fr

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