Scientists produce previously theoretical semiconducting 2D alloy

Semiconducting 2D alloys could be key to overcoming the technical limitations of modern electronics, and now scientists from Japan Advanced Institute of Science and Technology (JAIST) have realized the first experimental demonstration of a particularly promising candidate: 2D silicon-germanium (Si-Ge) alloys. They have also shown that the electronic properties of these alloys can be fine-tuned by simply adjusting the silicon-to-germanium ratio, paving the way for novel applications.

Alloys are materials composed of a combination of different elements or compounds, and have played a crucial role in the technological development of humans since the Bronze Age. Today, alloying materials with similar structures and compatible elements is essential, as it allows the properties of the final alloy to be finely tuned.

The versatility provided by alloying naturally extends to the field of electronics. Semiconductor alloys are an area of active research because new materials will be needed to redesign the building blocks of electronic devices (transistors). In this regard, 2D semiconductor alloys are seen as a promising material for surpassing the technical limitations of modern electronics. Unfortunately, graphene, the carbon-based poster child for 2D materials, does not easily lend itself to alloying, which leaves it out of the equation.

However, there is an attractive alternative in silicene. This material is composed entirely of silicon atoms arranged in a 2D honeycomb-like structure reminiscent of graphene. If the properties of silicene could be tuned as required, the field of 2D silicon-based nanoelectronics would take off. Although alloying silicene with germanium had been theoretically predicted to yield stable 2D structures with properties tunable by the silicon-to-germanium ratio, this had not been realized in practice.

Now, a team of scientists from JAIST has experimentally demonstrated a new way to grow a silicene layer and stably replace a portion of its atoms with germanium, allowing them to fine tune some of its electrical properties. The scientists report their work in a paper in Physical Review Materials.

First, the scientists grew a single layer of 2D silicene on a zirconium diboride (ZrB₂) thin film that had been grown on a silicon substrate. They did this through the surface segregation of silicon atoms, which crystallize in a 2D honeycomb-like structure. But the resulting silicene layer was not perfectly flat; one-sixth of the silicon atoms were a bit higher than the rest, forming periodic bumps or 'protrusions'.

Next, the scientists deposited germanium atoms onto the silicene layer under ultrahigh vacuum conditions. Interestingly, both theoretical calculations and experimental microscopy and spectroscopy observations revealed that the germanium atoms would only replace the protruding silicon atoms. By adjusting the number of germanium atoms deposited, a Si-Ge alloy with a desired silicon-to-germanium ratio could be produced. The composition of the final material was Si_6-xGe_x, where x can be any number between 0 and 1.

The team then studied the effects of this adjustable silicon-to-germanium ratio on the electronic properties of the Si-Ge alloy. They found that its electronic band structure, one of the most important characteristics of a semiconductor, could be adjusted within a specific range by manipulating the composition of the material.

"Silicon and germanium are elements commonly used in the semiconductor industry, and we showed that it is possible to engineer the band structure of 2D Si-Ge alloys in a way reminiscent of that for bulk (3D) Si-Ge alloys used in various applications," said Antoine Fleurence, a senior lecturer at JAIST and lead author of the paper.

The implications of this study are important for multiple reasons. First, the thinness and flexibility of 2D materials means they could be easily integrated in electronic devices for daily life. Second, the results could pave the way for a breakthrough in electronics.

"Semiconducting 2D materials made of silicon and germanium with atomically-precise thickness could further decrease the dimensions of the elemental bricks of electronic devices," explained Yukiko Yamada-Takamura, a professor at JAIST and a co-author of the paper. "This would represent a technological milestone for silicon-based nanotechnologies."

This story is adapted from material from Japan Advanced Institute of Science and Technology, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.