A new semiconductor that manipulates light in the invisible infrared terahertz range has been created by researchers at UC Santa Barbara.
Among the applications that this unique semiconductor will be able to support are more efficient solar cells, enhanced medical imaging, and the ability to transmit huge amounts of data at higher speeds.
The use of erbium is a central part of this technology. Erbium, a rare earth metal, has the ability to absorb light in the visible as well as infrared wavelength. It has long been used to enhance the performance of silicon in the production of fiber optics.
Combining erbium with the element antimony (Sb), the researchers embedded the resulting compound, erbium antimonide (ErSb), as semimetallic nanostructures within the semiconducting matrix of gallium antimonide (GaSb).
Nanostructures Coherently Embedded in Atomic Lattice
Erbium antimony, according to Lu, is a perfect material to match with GaSb, due to its structural compatibility with the surrounding material. This quality allowed the researchers to embed the nanostructures without interrupting the atomic lattice structure of the semiconducting matrix.
The less flawed the crystal lattice structure of a semiconductor is, the more reliable and better performing the device in which it is used will be.
Epitaxy refers to a process by which layers of material are deposited atom by atom, or molecule by molecule, one on top of the other with a specific orientation.
Single Crystal Heterostructured Semiconductor
Although semiconductors incorporating different materials have been studied for years, a single crystal heterostructured semiconductor/metal is in a class of its own.
The nanostructures enable the compound semiconductor to absorb a wider spectrum of light. This is because of the phenomenon called surface plasmon resonance, said Lu. The effect has potential applications in a broad range of research fields, such as solar cells, medical applications to fight cancer, and in the new field of plasmonics.
Optics and electronics operate on very different scales. Electron confinement is possible in spaces far smaller than light waves. Consequently, an ongoing challenge for engineers has been to create a circuit that can take advantage of the speed and data capacity of photons and the compactness of electronics for information processing.
The valuable bridge between optics and electronics could be found with this compound semiconductor using surface plasmons, electron oscillations at the surface of a metal excited by light.
When light, in this case, infrared, hits the surface of this semiconductor, electrons in the nanostructures begin to resonate, moving away from their equilibrium positions and oscillating at the same frequency as the infrared light, preserving the optical information, but shrinking it to a scale that would be compatible with electronic devices.
Broadband Polarization Effect
In the field of imaging, embedded nanowires of erbium antimonide offer a strong broadband polarization effect, according to Lu, filtering and defining images with infrared and even longer-wavelength terahertz light signatures.
This effect can be used to image a variety of materials, including the human body, without the risk posed by the higher energies that emanate from X-rays, for instance.
Chemicals such as those found in explosives and some illegal narcotics have unique absorption features in this spectrum region. The researchers have already applied for a patent for these embedded nanowires as a broadband light polarizer.
While infrared and terahertz wavelengths offer much in the way of the kind of information they can provide, the development of instruments that can take full advantage of their range of frequencies is still an emerging field.
Hong Lu, Daniel G. Ouellette, Sascha Preu, Justin D. Watts, Benjamin Zaks, Peter G. Burke, Mark S. Sherwin, Arthur C. Gossard. Self-Assembled ErSb Nanostructures with Optical Applications in Infrared and Terahertz. Nano Letters, 2014; 14 (3): 1107 DOI: 10.1021/nl402436g
_ Image courtesy of University of California - Santa Barbara_