Contacting carbon nanotubes with palladium (Pd) greatly reduces or eliminates the barriers for current, according to researchers from Stanford and Purdue universities (Nature, August 7, 2003). The researchers have realised high-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers.

Contacting carbon nanotubes with palladium (Pd) greatly reduces or eliminates the barriers for current, according to researchers from Stanford and Purdue universities (Nature, August 7, 2003). The researchers have realised high-performance ballistic nanotube field-effect transistors with zero or slightly negative Schottky barriers.

Normal metal contacts with nanotubes create a Schottky barrier. This inhibits current flow. Palladium is a noble metal with a large work function and good wetting interactions with nanotubes.

With Pd contacts, the "on" states of semiconducting nanotubes can behave as ohmically contacted ballistic metallic tubes. In ballistic conduction, the charge carriers travel from one contact to another without scattering. Normal conduction involves a large number of scattering events that creates a large resistance to current flow.

Room temperature conductances for the palladium-contacted tubes are near the ballistic limit of 4e2/h. Currents can reach up to 25microA per tube. At high voltages, current saturation appears to be set by backscattering of the charge carriers by optical phonons.

Previous conductances for such FET arrangements have been at most 0.30 of the ballistic value. Some conductances can be as low as 0.001. In the Stanford/Purdue experiments, conductances up to 0.65 of 4e2/h are seen at room temperature.

In terms of modelling, a diffusive model of the short (300nm) tube FETs completely fails to reproduce the device characteristics. Preliminary analysis using a ballistic MOSFET model leads to a good but not ideal fit. The researchers are not quite sure why palladium has such good properties, while other noble metals like platinum do not.

AngelTech Live III: Join us on 12 April 2021!

AngelTech Live III will be broadcast on 12 April 2021, 10am BST, rebroadcast on 14 April (10am CTT) and 16 April (10am PST) and will feature online versions of the market-leading physical events: CS International and PIC International PLUS a brand new Silicon Semiconductor International Track!

Thanks to the great diversity of the semiconductor industry, we are always chasing new markets and developing a range of exciting technologies.

2021 is no different. Over the last few months interest in deep-UV LEDs has rocketed, due to its capability to disinfect and sanitise areas and combat Covid-19. We shall consider a roadmap for this device, along with technologies for boosting its output.

We shall also look at microLEDs, a display with many wonderful attributes, identifying processes for handling the mass transfer of tiny emitters that hold the key to commercialisation of this technology.

We shall also discuss electrification of transportation, underpinned by wide bandgap power electronics and supported by blue lasers that are ideal for processing copper.

Additional areas we will cover include the development of GaN ICs, to improve the reach of power electronics; the great strides that have been made with gallium oxide; and a look at new materials, such as cubic GaN and AlScN.

Having attracted 1500 delegates over the last 2 online summits, the 3rd event promises to be even bigger and better – with 3 interactive sessions over 1 day and will once again prove to be a key event across the semiconductor and photonic integrated circuits calendar.

So make sure you sign up today and discover the latest cutting edge developments across the compound semiconductor and integrated photonics value chain.

REGISTER FOR FREE

VIEW SESSIONS