Nanotechnology researchers based in China have discovered a novel approach to synthesizing nanowires. Not only will the new material aid high-speed optical communication, but it may also avoid future dependency on silicon, or rare earth minerals, such as germanium.

Modern high-speed optical communication networks carry a 1550 nm infrared light (IR) signal. This light signal is then converted into an electrical signal for computer processing. Decent high-speed communication is therefore dependent on a fast conversion of the light signal to an electrical signal.

The requirements of materials to perform this task are highly technical, as the scientific journal Phys.orgexplains, “According to quantum theory, 1550 nm IR has energy of ~ 0.8 eV, and can only be detected by semiconductors with bandgaps lower than 0.8 eV, such as germanium (0.66 eV) and III-V compound materials such as InxGa1-xAs (0.35-1.42 eV) and InxGa1-xSb (0.17-0.73 eV).”

Morphology and chemical composition of InxGa1−xSb nanowires. a Scanning electron microscopy image of the new nanowires (NWs). bTransmission electron microscopy image and (cf) energy dispersive X-ray spectroscopy mapping of a NW. The gray scales denote the measured intensity. The color scales stand for the normalized concentration of Au, In, Ga and Sb measured, while the value of 1 represents the maximum concentration of each element detected. 

While these materials are effective, they often contain natural defects in the crystals which can substantially degrade photoresponse performance. By synthesizing nanowires in laboratory conditions, the scientists have been able to produce a material with similar properties to convert a light signal to an electrical signal, but at greater speeds as they contain fewer flaws.

The study was based at the Process Engineering (IPE) of the Chinese Academy of Sciences, City University of Hong Kong (CityU) where a team was able to catalytically grow highly crystalline ternary In0.28Ga0.72Sb nanowires from a metal catalyst such as nickel or gold.

The results from these new nanowires were surprisingly good, and clearly met or surpassed current communication technology standards. As Phys.org describes, “In the study, the In0.28Ga0.72Sb nanowires (bandgap 0.69 eV) showed a high responsivity of 6000 A/W to IR with high response and decay times of 0.038ms and 0.053ms, respectively, which are some of the best times so far.”

a. Transmission electron microscopy (TEM) image of a representative nanowire (NW). b. High-resolution TEM image of the tip region of the NW imaged in panel (a) c. High-resolution TEM image of the body region of the NW imaged in panel (a). d Lattice fringes of the body region of the NW. Inset displays the corresponding FFT pattern.

According to Prof. Johnny C. Ho, one of the study’s authors from CityU, “The fast IR response speed can be attributed to the minimized crystal defects, as also illustrated by a high hole mobility of up to 200 cm2/Vs.”

Crucial to the breakthrough was the use of a new technique developed by Ho’s group, called ‘catalyst epitaxy technology’. It was this new approach that minimized the number of defects, and therefore improved performance.

As Prof. Han Ningof IPE and the study’s senior author, says, “The catalyst nanoparticles play a key role in nanowire growth as the nanowires are synthesized layer by layer with the atoms well aligned with those in the catalyst.”

Illustrative schematics of four different proposed growth steps involved during the NW growth. They are: (i) formation of the gold (Au) nanoparticle, (ii) formation of the AuIn alloy, (iii) In precipitation from the AuIn alloy, (iv) formation of InxGa1−xSb neck with the increasing Ga concentration, and (v) growth of InxGa1−xSb NW with the steady Ga concentration

The team have now published their findings in the journal Nature Communications, where they report, “… the successful growth of high-quality InxGa1−xSb nanowires [NWs] with high hole mobility and efficient photosensing characteristics in both visible and short-wave (SW) IR regimes.”

Adding that, “[The nanowires] efficient response in the tens of microsecond range represents one of the fastest responses among all NW IR photodetectors reported. Importantly, these NWs can also be fabricated into NW parallel arrays-based devices, demonstrating their technological potential as active materials for next-generation, ultrafast and efficient room-temperature photodetectors.”


Photo credit:Nature Communications, & Neel