In order to save energy, the components of power electronics must become more and more efficient. Because they ensure that the electricity from photovoltaic or wind power plants is optimally fed into the power grid, that the drive system of railways is supplied with suitable electricity from the contact wire or that the motor in electric and hybrid motor vehicles is operated with electricity from the batteries. Of course, these components themselves should consume as little electricity as possible, because this would unnecessarily generate heat that has to be dissipated through cooling and therefore represents wasted energy.
Here, components made of the universal semiconductor material silicon reach their limits due to its material properties. Silicon carbide (SiC), a compound of silicon and carbon, is more suitable. Its properties are impressive: high-voltage resistant, high-temperature resistant, chemically robust, and suitable for higher switching frequencies, which can provide a further increase in efficiency. For years, SiC components have been used increasingly and very successfully.
SiC MOSFETs obtain their functionality from the interface between SiC and a very thin layer of silicon oxide applied to it. However, it is precisely this interface that presents researchers with major challenges: At the interface, unwanted defects occur during production that trap electrical charge carriers and thus reduce the current in the component. The investigation of these defects is therefore extremely important in order to fully exploit the potential of the material.
Conventional methods for investigating the properties of MOSFETs, usually originating from the silicon world, do not take these defects into account at all. Other, more complex measurement methods are either not practicable on a large scale or cannot be applied to finished components at all. For this reason, researchers at the FAU's Chair of Applied Physics have been looking for new ways to better investigate these flaws - and have found what they are looking for. They have noticed that the interface defects always follow the same pattern. "We have represented this pattern with a mathematical formula," explains doctoral student Martin Hauck. "In this way we can so cleverly include the interfacial defects in the calculation that not only the results of the usual parameters such as electron mobility or input voltage can be precisely determined. In addition, the concentration and distribution of the defects is determined almost incidentally".
In experiments carried out by the physicists with the aid of tailor-made transistors from the industrial partner Infineon Technologies Austria and its subsidiary Kompetenzzentrum für Automobil- & Industrie-Elektronik, the particularly simple method proved to be especially accurate. The precise insight into the innermost part of the field-effect transistors now allows better and shorter innovation cycles: in this way, procedures to reduce defects can be evaluated precisely, quickly, and easily; and the development of new, energy-saving power electronics can be accelerated accordingly.