According to the PSI team, using the world's top-performing source of soft X-rays at PSI's Swiss Light Source (SLS), they discovered that when going into the high power regime of the gallium nitride transistor, in specific directions, the electrons move more efficiently.
They believe this insight will help to develop faster and more powerful transistors – a prerequisite for converting our communication network to the coming 5G standard.
The researchers explain that high-electron-mobility transistors (HEMT) may be the key to commercialising 5G due to the demands in frequency, data rates, network density and energy.
HEMT electrons can move freely in a layer one-millionth of a millimetre thick between two semiconductors. In the PSI experiment, researcher Vladimir Strocov and his colleagues looked at how one might, through construction of a HEMT, contribute to an optimal flow of electrons.
The HEMT that Strocov and his team studied, made from aluminium nitride and gallium nitride, has a six-fold symmetry in its interface layer. There are six equivalent orientations along the atomic chains.
To investigate the flow of electrons within the interface layer, the researchers placed their HEMT under a very special microscope – examining the propagation speeds of the electrons: the angle-resolved photoelectron spectroscopy (ADRESS beamline) of the SLS.
Up till now, ARPES has been carried out with light sources in the ultraviolet range, but Strocov and his team used the high-energy X-ray light of SLS to do it.
With it, the researchers were able to lift out electrons from deep inside the conducting layer of the HEMT and then guide them into a measuring instrument that determined their energy, speed, and direction.
That is the first time it has been possible to make the fundamental properties of electrons in a semiconductor heterostructure visible, says Vladimir Strocov.
According to the team, the unique instrumentation of SLS provided them with important scientific results. It showed ways in which HEMT structures with higher operating frequencies and performance could be developed.
The fact that the electrons prefer a particular direction of flow can be exploited technically. Strocov explains: “If we orient the atoms in the gallium nitride HEMT so that they match the electrons' direction of flow, we get a significantly faster and more powerful transistor.”
With the present insights from their experiment, the researchers estimate the performance of radio transmitters could be increased yet again by around 10%. For mobile communication networks, this means fewer transmitter stations would be required to provide the same network coverage and power – and with that, reductions worth millions in maintenance and energy costs.