Tue. Aug 9th, 2022

New nanostructure may be the key to quantum electronics

Extremely precise interface between the two materials. Credit: Vienna University of Technology

A new electronic component from TU Wien (Vienna) can be an important key to the era of quantum information technology: Using a special manufacturing process, pure germanium is bonded with aluminum in a way that creates atomically sharp interfaces. This results in a so-called monolithic metal-semiconductor-metal heterostructure.


This structure shows unique effects that are particularly evident at low temperatures. Aluminum becomes superconducting – but not only that, this property is also transferred to the adjacent germanium semiconductor and can be specifically controlled by electric fields. This makes it excellently suited for complex applications in quantum technology, such as quantum bit processing. A particular advantage is that using this approach, it is not necessary to develop completely new technologies. Instead, mature and well-established semiconductor fabrication techniques can be used to enable germanium-based quantum electronics. The results have now been published in the journal Advanced materials.

Germanium: difficult to form high quality contacts

“Germanium is a material that is recognized for playing an important role in semiconductor technology for the development of faster and more energy efficient components,” says Dr. Masiar Sistani from the Institute for Solid State Electronics at TU Vienna. “But if one intends to use it to produce components on a nanometer scale, one encounters a major problem: It is extremely difficult to produce high quality electrical contacts, because even the smallest impurities at the contact points can have a major impact on The electrical properties. We have therefore set ourselves the task of developing a new manufacturing method that enables reliable and reproducible contact properties. “

Travel atoms

The key to this is temperature: when nanometer-structured germanium and aluminum are brought into contact and heated, the atoms in both materials begin to diffuse into the neighboring material — but to a very different extent: the germanium atoms move rapidly into the aluminum, whereas aluminum hardly diffuses into germanium at all. “If you thus connect two aluminum contacts to a thin germanium nanowire and raise the temperature to 350 degrees Celsius, the germanium atoms diffuse out of the nanowire. This creates empty spaces where aluminum can easily penetrate,” explains Masiar Sistani. “In the end, only a few nanometer range in the middle of the nanowire consists of germanium, the rest has been filled up with aluminum.”

Normally, aluminum consists of small crystal grains, but this new manufacturing method forms a perfect single crystal, where the aluminum atoms are arranged in a uniform pattern. As can be seen under the transmission electron microscope, a completely pure and atomically sharp transition is formed between germanium and aluminum, with no disordered region in between. Unlike conventional methods where electrical contacts are applied to a semiconductor, e.g. Upon evaporation of a metal, no oxides can be formed at the boundary layer.

Feasibility check in Grenoble

To take a closer look at the properties of this monolithic metal-semiconductor heterostructure of germanium and aluminum, Masiar Sistani collaborated with Professor Olivier Buisson’s quantum engineering group at the University of Grenoble. It turned out that the new structure actually has quite remarkable properties: “Not only were we able to demonstrate superconductivity in pure, undoped germanium for the first time, we could also show that this structure can be switched between quite different operating modes using of electric fields, “reports Dr. Masiar Sistani. “Such a germanium quantum dot device can not only be superconducting but also completely insulating, or it can behave like a Josephson transistor, an important basic element in quantum electronic circuits.”

This new heterostructure combines a wide range of advantages: The structure has excellent physical properties required for quantum technologies, such as high carrier mobility and excellent manipulation of electric fields, and it has the added advantage of being well suited to already established microelectronics technologies: Germanium are already used in current chip architectures and the temperatures required for heterostructure formation are compatible with mature semiconductor treatment schemes. “We have developed a structure that not only has theoretically interesting quantum properties, but also opens up a technologically very realistic opportunity to enable new and energy-saving devices,” says Dr. Masiar Sistani.


Reliable and extremely fast quantum calculations with germanium transistors


More information:
Jovian Delaforce et al., Al – Ge – Al Nanowire Heterostructure: From Single -Hole Quantum Dot to Josephson Effect, Advanced materials (2021). DOI: 10.1002 / adma.202101989

Provided by Vienna University of Technology

Citation: New nanostructure may be the key to quantum electronics (2021, October 11) retrieved October 11, 2021 from https://phys.org/news/2021-10-nanostructure-key-quantum-electronics.html

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