Practically all semiconductors today utilize silicon with a cubic crystal structure because the material naturally crystallizes that way. Researchers, however, have created a hexagonal silicon structure, opening up the possibility of more novel properties compared to what cubic silicon is capable of.
In a study published in the journal Nano Letters, Erik P.A.M. Bakkers and colleagues detailed their work, explaining that normal cubic silicon is not capable of emitting light because it has an indirect band gap. According to calculations though, adding germanium to hexagonal silicon can address this problem.
Light emission has been an important goal for the electronics industry for over four decades. With the creation of hexagonal silicon, it is now possible to integrate optical communicate on electronic chips directly.
The study is the first clear demonstration of what can be done with pure hexagonal silicon but this is not the first time that the material was produced. However, earlier methods made it difficult to control the formation of the crystal and didn't offer the ability to verify the structure unambiguously.
These issues were addressed in the study as the researchers used new means to fabricate the material and characterize structure. The new fabrication method utilizes a hexagonal nanowire template heated to high temperatures. When silicon was deposited on the template, a high-quality hexagonal structure was the result. Nanowires grow vertically so there were no overlaps that could impede measurements that have to be taken for characterizing the hexagonal structure, allowing for a more certain verification.
The researchers are hopeful that the new fabrication method they developed will make it possible for hexagonal silicon to be fully assessed, shedding light on what the material's properties exactly are, leading to the creation of a new class of semiconductors for the electronics industry to use.
In the future, the researchers are planning to use the same method they devised to come up with hexagonal germanium and compounds containing silicon and germanium.
"The next step is to mix in germanium and study the optical properties," said Bakkers, adding that their methods appear to be effective but are still works in progress.
Other authors for the study include: Julian Stang, Simone Assali, Ang Li, Sebastian Kolling, Paolo Postorino, Francesco Capitani, Claudia Fasolato, Ilaria Zardo, Dominik Kreigner, Marc Watzinger, Tanja Etzelstorfer, Sonia Conesa-Boj, Marcel A. Verheijen and Hakon Ikaros T. Hauge.
Photo: Yuri Samoilov | Flickr