The researchers grew gallium arsenide nanowires epitaxially on silicon substrates. Then they enclosed the wafer-thin wires in another layer of material to which they added indium. The mismatched crystal structure of the materials was intended to induce a mechanical strain in the wire core that would change the electronic properties of the gallium arsenide — for example, cause the bandgap to become smaller or the electrons to become more mobile. To magnify this effect, the scientists kept adding indium to the shell, increasing the shell’s thickness.
![Semiconductor nanowires can be tuned over wide energy ranges, HZDR.](https://www.photonics.com/images/Web/Articles/2019/7/1/REAS_Helmholtz_Zentrum_Labo.jpg)
“What we did was take a known effect to extremes,” researcher Emmanouil Dimakis said. “The 7% of strain achieved was tremendous.” The team confirmed its discovery by conducting several independent series of measurements at facilities in Dresden and at the high-brilliance x-ray light sources PETRA III in Germany and Diamond in England.
The researchers next examined what triggered the extremely high strain in the nanowire core, and how this could be applied. They found that the high strain let them shift the bandgap of the gallium arsenide semiconductor to very low energies, making it compatible even for wavelengths of fiber optic networks — a spectral range that could previously only be achieved using alloys containing indium. The nanowires exhibited a reduction of their bandgap by up to 40% when overgrown with lattice-mismatched indium gallium arsenide or indium aluminium arsenide shells.
The researchers believe that the resulting bandgap reduction could make gallium arsenide nanowires suitable for photonic devices across the near-infrared (NIR) range, including telecom photonics at 1.3 μm and potentially 1.55 μm, with the additional possibility of monolithic integration in silicon-CMOS chips. “Scientists have been aware of gallium arsenide as a material for years, but nanowires are special. A material may exhibit completely new properties at the nanoscale,” Dimakis said.
The research was published in Nature Communications (http://dx.doi.org/10.1038/s41467-019-10654-7).