Innovative semiconductor material produced for the first time using MOVCD process
Scientists at the Fraunhofer Institute for Applied Solid State Physics IAF (Freiburg, Germany) have succeeded for the first time worldwide in producing aluminium scandium nitride (AlScN) by metalorganic chemical vapor deposition (MOCVD). Components based on AlScN are regarded as the next but one generation of high-performance electronics. Fraunhofer IAF is thus taking a decisive step towards its goal of manufacturing power electronics for industrial applications based on transistors made of AlScN.
Transistors based on AlScN are considered promising for use in industrial applications such as data transmission, satellite communications, radar systems and autonomous driving. Silicon (Si) based devices are increasingly reaching their physical limits in these applications. This means that Si components can no longer become smaller. And if the ever-increasing amounts of data had to be processed with the current Si technology, the server rooms would occupy such a large area that it would be economically and ecologically unacceptable.
HEMTs (high electron mobility transistors) surpass the possibilities of Si components many times over. The properties of the underlying materials are decisive for the success of HEMT structures. AlScN has properties that allow higher carrier concentrations than other materials. In the future, significantly more powerful and efficient HEMTs will be realized with AlScN.
Previous manufacturing processes fail due to quality and productivity
However, processing AlScN poses critical challenges. According to the state of the art, AlScN layers can be produced by sputtering. However, the quality of these layers is not sufficient for electronic applications such as high performance transistors. Alternatively, it is possible to produce AlScN by molecular beam epitaxy (MBE). With this process, high scandium contents can be obtained in the compound. The quality is also sufficient for the production of microelectronic components. However, the process is complex and the productivity is too low to be used industrially.
MOCVD promises production suitable for industrial use
The production of AlScN by MOCVD promises both quality and productivity sufficient for industrial applications. “We knew that in the past, researchers had tried to produce gallium scan dium nitride using MOCVD, but were unsuccessful. We also know that many researchers around the world are working to develop AlScN transistors, but no one before us has made it using MOCVD, although this could be a promising path for the industry,” explains Stefano Leone, group leader at Fraunhofer IAF. In the MOCVD process, gas is passed over a heated wafer. The thermal effect releases certain molecules from the gas that integrate into the crystal structure of the wafer. By regulating the gas flow, temperature and pressure, the crystal composition can be precisely adjusted and the growth of different layers of material on top of each other is also possible through the rapid exchange of gases.
The challenge for the researchers is that there is no gas for scandium. The molecules (precursors) for scandium are very large and difficult to bring into the gas phase. “We have investigated what might be the best precursor for scandium and considered how our MOCVD reactor could be rebuilt for the necessary processes. We did a lot of research and discussion and finally developed a setup that we are now even patenting. Ultimately, we managed to grow AlScN layers by MOCVD with very high crystal quality and the right amount of scandium to develop the next generation of electronic power transistors,” Leone says. The MOCVD system at Fraunhofer IAF has been rebuilt by the research group to enable a high quality and reproducible AlScN manufacturing process.
After the successful deposition of the AlScN in the MOCVD system, the first AlScN layers for transistors were produced. With a resistance of ~200 ohm/sq., a mobility of ~600 cm²/Vs and a carrier density of ~4.0 x 10 ¹³ cm-², these layers already achieve promising results. The aim of the researchers is now to reduce resistance, increase mobility and further optimize material quality. The aim is to further improve the performance of future transistors and to bring Fraunhofer IAF closer to its goal of providing AlScN-HEMTs for industrial power electronic applications.
Original publication (in German): https://www.iaf.fraunhofer.de/de/medien/pressemitteilungen/aluminiumscandiumnitrid-per-mocvd.html
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