New electronic component could play key role in quantum electronics

A new electronic component from TU Wien (Vienna) could play a key role in the development of quantum information technology. Through a bespoke manufacturing process, pure germanium is bonded to aluminum to allow the creation of atomically clean interfaces.

Research detailing this new process has been published in Advanced materials.

Develop the new approach

This results in a monolithic metal-semiconductor-metal heterostructure, which shows unique effects at low temperatures. At these low temperatures, the aluminum becomes superconducting and this property is transferred to the adjacent germanium semiconductor. This also allows it to be controlled specifically with electric fields.

These characteristics make it particularly useful for complex applications in quantum technology. In particular, it can be used to process quantum bits. The approach does not require the development of entirely new manufacturing technologies since existing semiconductors Manufacturing techniques can be used to activate germanium-based quantum electronics.

Dr Masiar Sistani is from the Institute for Solid State Electronics at TU Wien.

“Germanium is a material that will certainly play an important role in semiconductor technology for the development of faster and more energy efficient components,” says Dr Sistani.

Interface between the two materials. (Image: TU Vienna)

Take on the challenge

Major problems arise if it is used to produce components at the nanoscale. In particular, the material makes it difficult to produce high quality electrical contacts due to the high impact of small impurities at the contact points, which can significantly alter the electrical properties.

“We have therefore set ourselves the task of developing a new manufacturing method that allows reliable and reproducible contact properties,” explains Dr Sistani.

The key to this approach is temperature. When germanium and nanoscale aluminum come into contact and are heated, the atoms of the two materials begin to diffuse into the other material. However, this happens to varying degrees.

Germanium atoms move quickly in aluminum, although the latter hardly diffuses.

“So if you connect two aluminum contacts to a thin germanium nanowire and raise the temperature to 350 degrees Celsius, the germanium atoms will diffuse around the edge of the nanowire. This creates empty spaces which the aluminum can then easily penetrate, ”explains Dr Sistani. “In the end, only an area of ​​a few nanometers in the middle of the nanowire is made of germanium, the rest was filled with aluminum.”

The new manufacturing method forms a single perfect crystal in which the aluminum atoms are arranged in a uniform pattern. This is different from normal aluminum, which is made up of tiny grains of crystal. This allows for an atomically clean transition between germanium and aluminum.

“Not only were we able to demonstrate superconductivity in pure, undoped germanium for the first time, but we were also able to show that this structure can be switched between quite different operating states using electric fields. 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 building block of quantum electronic circuits, ”explains Dr Sistani.

Besides their theoretical applications, these new structures could have a significant impact on future quantum devices.

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