How to control the excitation of electronics

An international team of scientists have made an important step towards the control of excitonic effects in two-dimensional van der Waals heterostructures. Published in the journal Nature Physics, their research could in future help to create electronics with more controlled properties.

The creation of two-dimensional semiconductor materials is one of the most important areas of modern materials science, as these materials can be the basis for elements needed to create the next generation of electronics. One 2D material with suitable electronic characteristics is two-dimensional molybdenum disulfide (MoS₂), which has a single-layer structure (one atom layer) of molybdenum located between two sulfur layers: this material has a high charge mobility and high on/off in the transistor element.

In 2017, Professor Gotthard Seifert from Russia’s National University of Science and Technology MISIS described the mechanism of defect germination in the structure of two-dimensional MoS₂ as a process that will make it possible for scientists to capitalise on two-dimensional MoS₂’s full potential use in microelectronics. Monolayers of molybdenum disulfide (and, for example, wolframite diselenides — WSe₂) have shown exceptional optical properties due to the presence of excitons: tightly bound pairs of electron holes (quasiparticles acting as a carrier of a positive charge). At the same time, the creation of the MoS₂/WSe₂ heterostructure by laying separate monolayers on each other leads to the appearance of a new type of exciton in it, where the electron and the hole are spatially divided into different layers.

International scientists including Professor Seifert have now shown that interlayer excitons give a very specific optical signal display when layered. This allows scientists to study quantum phenomena, making it ideal for experiments in volitronics (a field of quantum electronics) to control electrons in the ‘valleys’ of semiconductors — the local minimum of an element’s conduction zone. In the future, these breakthroughs could lead to the most effective way to code information (by placing an electron in one of these valleys).

“Thanks to the use of spectroscopic methods and quantum-chemical calculations from the first principles, we have revealed a partially charged electron hole in MoS₂/WSe₂ heterostructures, as well as [the electron hole’s] location,” said Professor Seifert, one of NUST MISIS’s leading scientists. “We have managed to control the radiation energy of this new exciton by changing the relative orientation of the layers.”

According to Professor Seifert, this result is an important step towards understanding and controlling exciton effects in van der Waals heterostructures (where these distance-dependent atomic interactions occur). The research team is continuing to study the effect of layer rotations on the material’s electronic properties. In the future, this will allow for the creation of new materials for solar panels or electronics.

Image caption: Molybdenum atoms. Image ©NUST MISIS