Scientists in TU Wien in Vienna used a special manufacturing process to bond pure germanium with aluminum that created atomically sharp interfaces, making it suitable for complex applications in quantum technology.
Phys.org reported that it resulted in a novel nanostructure called monolithic metal-semiconductor-metal heterostructure. It demonstrates that aluminum becomes superconducting and transfers that property to the adjacent semiconductor to control electric fields, processing quantum bits. Researchers noted that one of the advantages of using this approach is enabling germanium-based quantum electronics.
Using Germanium to Develop Quantum Technology
Quantum technology is an emerging field of physics and engineering. Quantum technology expert Paul Martin defines quantum technology as a class of technology that uses the principles of quantum mechanics or the physics of sub-atomic particles, such as quantum entanglement and quantum superposition.
Humans use quantum technology in nuclear power and smartphones, using semiconductors that employ quantum physics to function. It also promises more reliable navigation and timing systems, secure communications, more accurate healthcare imaging, and more powerful computing.
In a paper published in 2020 in the journal Nature Reviews Materials, researchers said that geranium is an emerging versatile material to develop quantum technologies capable of encoding, processing, and transmitting quantum information. They argue that germanium-based systems could be the key building blocks for quantum technology because of their strong spin-orbit coupling and ability to host superconducting correlations.
But Dr. Masiar Sistani from the Institute for Solid State Electronics at TU Wien said it is extremely difficult to produce high-quality electrical contacts when germanium is turned into a nanoscale. So, they looked for a way to manufacture them that would result in a faster and more energy-efficient nanostructure.
The Key is Temperature
In the study, titled "Al-Ge-Al Nanowire Heterostructure: From Single-Hole Quantum Dot to Josephson Effect," published in Advanced Materials, researchers found that temperature plays a key role in achieving their goal.
When the nanometer-size germanium and aluminum are brought into contact and heated, their atoms begin to diffuse into neighboring materials in which atoms of germanium move to aluminum and vice versa, Phys.org reported. When they raised the temperature to 350 degrees Celsius, germanium atoms diffused off the edge of the nanowire, creating empty spaces where aluminum could penetrate.
This special manufacturing process forms a perfect single crystal wherein aluminum atoms are arranged in a uniform pattern, as seen under the transmission electron microscope. Not a single atom is disordered in contrast to conventional methods where electrical contacts are applied to a semiconductor.
Researchers were able to show that this monolithic metal-semiconductor heterostructure of germanium and aluminum demonstrates superconductivity in pure germanium for the first time.
More so, Dr. Masiar Sistani said that it shows that this nanostructure can be switched into different operating states using electrical fields, which means the germanium quantum dot can be superconducting and insulating such as the Josephson transistor.
This novel nanostructure combines various advantages for quantum technology, such as high carrier mobility, excellent manipulability, and it fits well with established microelectronics technologies.
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