Leakage-free germanium nanowire transistor beats silicon

February 09, 2017 // By Julien Happich
With its high electron mobility, germanium is a tantalizing material to work with. But due to its low band-gap energy (0.66 eV), so far the development of germanium-based devices has been hindered by a high reverse junction leakage, dramatically raising static power dissipation.

Using a germanium nanowire as a non-doped channel, a team of researchers from the Nanoelectronic Materials Laboratory (NaMLab GmbH) and the Cluster of Excellence Center for Advancing Electronics Dresden (cfaed) at the Dresden University of Technology has devised a dual-gate transistor that not only efficiently suppress leakage but can also be programmed between electron-(n) and hole-(p) conduction.

Top-view SEM image of a multi-gated germanium
nanowire transistor. The scale bar is 400nm

In a paper titled "Enabling Energy Efficiency and Polarity Control in Germanium Nanowire Transistors by Individually Gated Nanojunctions" published in the journal ACS Nano, the researchers report a device layout with two independent gates used to induce an additional energy barrier to the channel that blocks the undesired carrier type.

The researchers show that the polarity of the same doping-free device can be dynamically switched between p- and n-type, outperforming previous polarity-controllable device concepts on other material systems in terms of threshold voltages and normalized on-currents.

Schematic device layout showing
the program gate and the control gate.

Although the concept is proven experimentally (and the results corroborated using finite-element analysis) with a germanium nanowire Schottky barrier field effect transistor (FET), the researchers reckon that the same basic approach of having multiple gates is transferable to other types of FETs, , including tunnel FETs, spin-FETs or junctionless transistors.