February 26, 2024

Speeding Through Semiconductor Nanowires: New Basis for Ultrafast Transistors

Electron mobility plays a crucial role in this: The faster electrons can accelerate in these tiny wires, the faster a transistor can change and the less energy it needs. A team of scientists from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the TU Dresden, and NaMLab has now been successful in experimentally showing that electron mobility in nanowires is incredibly improved when the shell positions the wire core under tensile strain. What we did not understand was the level to which the wire shell would impact electron movement in the core. A series of measurements and tests demonstrated this impact: Despite interaction with the shell, electrons in the core of the wires under investigation moved approximately thirty percent faster at space temperature than electrons in comparable nanowires that were strain-free or in bulk gallium arsenide.
The researchers determined electron movement by using contactless optical spectroscopy: Using an optical laser pulse, they set electrons free inside the product.

What we did not understand was the extent to which the wire shell would impact electron mobility in the core. A series of tests and measurements showed this impact: Despite interaction with the shell, electrons in the core of the wires under investigation moved roughly thirty percent quicker at space temperature than electrons in similar nanowires that were strain-free or in bulk gallium arsenide.
Exposing the core.
The scientists determined electron mobility by applying contactless optical spectroscopy: Using an optical laser pulse, they set electrons free inside the product. The scientists picked the light-pulse energy such that the shell appears practically transparent to the light, and totally free electrons are only produced in the wire core.
Comparing the outcomes with models reveals how the electrons relocation: The greater their speed and the fewer obstacles they encounter, the longer the oscillation lasts. “This is actually a basic technique. But this time we did not measure the entire wire– comprising the core and the shell– but only the small core. This was a new difficulty for us. The core accounts for around one percent of the material. Simply put, we thrill about a hundred times less electrons and get a signal that is a hundred times weaker,” specified Pashkin.
Consequently, the option of sample was also an important action. A common sample includes approximately around 20,000 to 100,000 nanowires on a piece of substrate determining approximately one square millimeter. If the wires are spaced even more detailed together on the sample, an unfavorable impact can take place: Neighboring wires engage with each other, producing a signal similar to that of a single, thicker wire, and distorting the measurements. The electron speed obtained is too low if this effect is not detected. To eliminate such disturbance, the Dresden research study team carried out additional modelling in addition to a series of measurements for nanowires with various densities.
Models for quick transistors
Patterns in microelectronics and the semiconductor industry increasingly demand smaller transistors that change ever much faster. Professionals expect that novel nanowire principles for transistors will likewise make inroads into industrial production over the next couple of years. The development achieved in Dresden is particularly promising for ultra-fast transistors. The scientists next action will be to develop the first models based upon the studied nanowires and to test their suitability for use. To do this, they plan to apply, test and enhance metal contacts on the nanowires, as well as checking the doping of nanowires with silicon and optimizing production processes.
Recommendation: “High electron movement in strained GaAs nanowires” by Leila Balaghi, Si Shan, Ivan Fotev, Finn Moebus, Rakesh Rana, Tommaso Venanzi, René Hübner, Thomas Mikolajick, Harald Schneider, Manfred Helm, Alexej Pashkin and Emmanouil Dimakis, 17 November 2021, Nature Communications.DOI: 10.1038/ s41467-021-27006-z.

Terahertz spectroscopy measurements showed that the stretched core of semiconductor nanowires can host fast moving electrons, an idea that could be used for a brand-new generation of nano-transistors. Credit: HZDR/Juniks
Nanowires under stress create the basis for ultrafast transistors.
Electron movement plays an essential role in this: The faster electrons can accelerate in these small wires, the faster a transistor can change and the less energy it requires. A group of researchers from the Helmholtz-Zentrum Dresden-Rossendorf (HZDR), the TU Dresden, and NaMLab has actually now prospered in experimentally showing that electron movement in nanowires is incredibly boosted when the shell puts the wire core under tensile stress.
Nanowires have a distinct residential or commercial property: These ultra-thin wires can sustain very high elastic pressures without harming the crystal structure of the product. And yet the materials themselves are not unusual. Gallium arsenide, for example, is commonly utilized in commercial production, and is known to have a high intrinsic electron mobility.
Tension develops speed
To further improve this mobility, the Dresden scientists produced nanowires consisting of a gallium arsenide core and an indium aluminum arsenide shell. “We affect the efficient mass of electrons in the core. The electrons end up being lighter, so to speak, which makes them more mobile,” explained Dr. Emmanouil Dimakis, researcher at the HZDRs Institute of Ion Beam Physics and Materials Research and initiator of the recently published study.