Researchers at the University of California, Santa Barbara (UCSB) have developed a recipe for creating a nearly perfect compound semiconductor that could lead to more efficient photovoltaics, safer and higher resolution biological imaging, and transmitting massive amounts of data at higher speeds.
The researchers took the rare earth element, erbium (Er), along with the element antimony (Sb) and made a compound of the two into semimetallic nanowires or nanoparticles. Then they embedded those nanostructures into the semiconducting matrix of gallium antimonide (GaSb). Because the arrangement of atoms within the ErSb nanostructures matches the pattern of the surrounding matrix, the compound semiconductor forms an uninterrupted crystal lattice capable of manipulating light energy in the mid-infrared range.
"The nanostructures are coherently embedded, without introducing noticeable defects, through the growth process by molecular beam epitaxy," said Hong Lu, a researcher in UCSB's Materials department, in a press release. Lu is the lead author of the study that revealed the new material, published in the journal Nano Letters. "Secondly, we can control the size, the shape and the orientation of the nanostructures." (Epitaxy is a manufacturing technique in which crystals are grown on a substrate.)
The ErSb nanoparticles and wires enable the compound semiconductor to absorb a wider spectrum of light due to a phenomenon called surface plasmon resonance. Surface plasmons are oscillations of electrons found on the interface between, for example, a metal and air. Surface plasmon resonance (SPR) is the collective oscillation of electrons due to light stimulation.
By exploiting SPR, the researchers believe that their new material could bridge the gap between optics and electronics. While photons offer the potential for computers that can handle data at very high speeds, it has been difficult to manipulate the relatively long wavelengths of light in the compact environment of electronics.
When infrared light strikes the material developed by the UCSB researchers, electrons in a ErSb nanostructure begin to resonate at the same frequency as the incident light. This oscillation of these electrons preserves the optical signal, but shrinks it to a scale where it is manageable for electronic devices.
According to the researchers, the highly conductive nanostructures can also polarize electromagnetic radiation in a broad range, providing a new platform for applications in the infrared and terahertz frequency ranges. The polarization effect could help in filtering and defining images with infrared and even longer-wavelength terahertz light signatures. This could make possible the imaging the internal structure of a variety of materials, including the human body, without the risk posed by using X-rays.
Dexter Johnson is a contributing editor at IEEE Spectrum, with a focus on nanotechnology.