Mix of semiconductors and quantum technology with a new composite

Researchers have identified a material that could integrate quantum devices into semiconductor technology, making electronic components considerably more powerful.

Scientists at the Paul Scherrer Institute PSI and Cornell University today publish their findings in the journal Scientists progress.

Today’s electronic infrastructure relies primarily on semiconductors, a class of materials that developed in the mid-20th century and has continued to improve since. Currently, the most significant challenges in semiconductor electronics include other improvements that would increase data transmission bandwidth, energy efficiency, and information security. The exploitation of quantum effects is likely to be a breakthrough.

The quantum effects that can occur in superconducting materials are particularly worth considering. Superconductors are materials in which the electrical resistance disappears when they are cooled below a certain temperature. The fact that quantum effects in superconductors can be used has already been demonstrated in the first quantum computers.

To find possible successors to today’s semiconductor electronics, some researchers – including a group from Cornell University – are studying what are called heterojunctions, that is, structures made of two different types of materials. More specifically, they study layered systems of superconducting and semiconductor materials. “It has been known for some time that it is necessary to select materials with very similar crystal structures for this, so that there is no stress in the crystal lattice at the contact surface”, explains John Wright, which produced the heterojunctions for the new study. at Cornell University.

Two suitable materials in this regard are superconducting niobium nitride (NbN) and semiconducting gallium nitride (GaN). The latter already plays an important role in semiconductor electronics and is therefore the subject of much research. Until now, however, it was not clear exactly how the electrons behave at the contact interface of these two materials – and whether it is possible for the electrons in the semiconductor to interfere with the superconductivity and thus erase the effects. quantum.

“When I came across the research of the Cornell group, I knew: here at PSI, we can find the answer to this fundamental question with our spectroscopic methods on the ADRESS beamline,” explains Vladimir Strocov, researcher at the source of SLS synchrotron light at PSI.

This is how the two groups came to collaborate. During their experiments, they finally discovered that the electrons of the two materials “stay with each other”. No unwanted interactions that could potentially spoil the quantum effects take place.

Synchrotron light reveals electronic structures

PSI researchers used a well-established method on the SLS ADRESS beamline: angular-resolution photoelectron spectroscopy using soft X-rays – or SX-ARPES for short. “With this method, we can visualize the collective movement of electrons in the material,” explains Tianlun Yu, postdoctoral researcher in Vladimir Strocov’s team, who carried out the measurements on the NbN / GaN heterostructure. Along with Wright, Yu is the first author of the new publication.

The SX-ARPES method provides a kind of map whose spatial coordinates show the energy of electrons in one direction and something like their speed in the other; more precisely, their momentum. “In this representation, the electronic states appear as light bands on the map,” explains Yu. The crucial research result: at the material boundary between niobium nitride NbN and gallium nitride GaN, the “bands” respective are clearly separated from each other. This tells researchers that electrons stay in their original material and do not interact with electrons in neighboring material.

“The most important conclusion for us is that the superconductivity in niobium nitride remains intact, even if it is placed atom by atom to correspond to a layer of gallium nitride,” says Vladimir Strokov. “With that, we were able to provide another piece of the puzzle that confirms: this layered system could in fact lend itself to a new form of semiconductor electronics that integrates and exploits the quantum effects that occur in superconductors. “

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