In recent times, an international research team led by Australia has successfully transformed the semiconductor material “germanium” into a superconductor material. This discovery paves the way for the development of scalable, energy-efficient quantum devices, with the potential to elevate chip-related technology industries to a whole new level.
Silicon and germanium (Ge) are crucial building blocks for modern chips and solar cells. If these materials can be endowed with superconducting capabilities, their operational speed and efficiency will be significantly enhanced. The superconducting properties of Group IV metals have long been a focus of research due to their potential applications in superconducting qubits and low-temperature complementary metal-oxide-semiconductor (CMOS) control circuits.
While germanium materials have high hole mobility and are easy to process, there have been numerous challenges in transforming them into superconductors. Previous attempts by scientists using various techniques to turn it into a superconductor have faced issues such as structural disorder, dopant clustering, inconsistent interfaces, and poor control of layer thickness, preventing electrons from freely moving to become superconductors.
This time, a research team led by the University of Queensland in Australia, along with New York University, Ohio State University, and ETH Zurich, successfully overcame these challenges using molecular beam epitaxy (MBE) technology, turning germanium into a high-quality low-temperature superconductor.
The team explained that both germanium and silicon have a diamond-like crystal structure, occupying a unique position between metals and insulators, and their versatility and durability have made them core materials in modern manufacturing. Industry uses doping techniques to alter the electrical properties of semiconductors, but most of the effects are unsatisfactory and inhibit the generation of superconductivity.
To impart superconducting properties to these elements, researchers discarded the traditional ion implantation method in favor of molecular beam epitaxy technology. Through precise growth temperatures (100-150°C) and atomic fluxes, they facilitated the low-temperature growth of germanium atoms by forming a floating layer of gallium atoms on the surface, allowing gallium atoms to effectively and stably replace some germanium atoms, ensuring the smoothness of the film surface and the crystalline properties of the monocrystals.
They observed the gallium substitution in these thin films through instruments. The results showed that up to 17.9% of germanium atoms were replaced by gallium, exceeding the standard solid solution limit and reaching the realm of “super-doping,” indicating their successful preparation of high-quality, heavily gallium-doped germanium films (Ga:Ge).
In addition to single-layer films, the research team also used a sandwich-like structure with two layers of Ga:Ge films with thicknesses of only a few nanometers (nm), sandwiching a layer of silicon (Si) a few nanometers in size to simulate a vertical Josephson junction structure. This type of superconductor structure can achieve a zero-resistance state at a temperature of 3.5K (approximately -270°C).
Furthermore, the method can replace the original silicon layer with a germanium metal layer, and the component still operates stably, achieving a zero-resistance state at 2K (approximately -271°C). Both cases demonstrate that this process can precisely control nanoscale thickness and interface quality.
Researchers observed through various instruments and electron microscopes that while gallium successfully replaced germanium atoms, it slightly deformed the crystal, but the overall structure remained stable.
In response, researchers stated that by altering the crystal structure, the IV group elements that do not exhibit superconductivity under normal conditions can form electron pairs to achieve superconducting characteristics. This research not only resolves the long-standing controversy about germanium’s inability to become a superconducting material but also paves the way for the development of scalable, energy-efficient quantum devices and low-temperature electronic components.
Javad Shabani, a physicist at New York University, explained, “Germanium metal is widely used in computer chips and optical fibers. If superconducting properties can be realized in germanium, it has the potential to revolutionize many consumer products and industrial technologies.”
Peter Jacobson, a physicist at the University of Queensland, added, “These materials have the potential to become the foundation for future quantum circuits, sensors, and low-power, low-temperature electronic devices, all of which require clear interfaces between superconducting and semiconductor areas.”
He continued, “Germanium is already a key material in advanced semiconductor technology, so by demonstrating that it can also exhibit superconductivity under controlled growth conditions. This experimental result holds promise for manufacturing scalable quantum devices directly for mass production.”
Julian Steele, a physicist at the University of Queensland and a co-author of the study, stated, “We did not use ion implantation but instead used molecular beam epitaxy to precisely incorporate gallium atoms into the germanium lattice. This technology is like growing a thin crystal layer inside the lattice, allowing for precise control of structural accuracy and performance to give it superconductivity.”
This research received partial funding from the U.S. Air Force Office of Scientific Research (FA9550-21-1-0338) and marks an important step in integrating superconducting properties into electronic materials, with the potential to reshape future computing and quantum technologies. The results of this study were published in the renowned journal “Nature” at the end of October.