(Invited) Epitaxy of Silicon Carbide for Power Devices

Abstract

We observe an evolution how electric power is generated, converted, distributed and used. The world making an attempt to move away from fossil fuels towards a more renewable, energy efficient and electrified energy ecosystems, and therefor efficiency in power conversion processes becomes critically important. As the most prominent example, various wide band gap semiconductor materials are entering the power electronics in electric and hybrid vehicles. Among them is a Silicon Carbide (SiC). A major benefit of its characteristics, comparing to Silicon (Si), in terms of switching speed, heat loss and size of power electronic devices, is at least 50 % reduction in energy loss in the form of heat. This saving translates into more efficient power electronics and more energy for an electric motor and therefore for longer mileage with the same battery. Therefore, SiC offers an opportunity to move power electronics beyond the boundaries set by the material limits of Si. From production point of view, SiC is especially attractive because of its compatibility with Si manufacturing technologies.Modern semiconductor power electronic devices are fabricated out of epitaxial thin films of semiconductors, creating a desired device’s layers stack. Therefore, the epitaxy is absolutely essential for creation of such devices.SiC is a fascinating material with excellent physical properties. It is a wide band gap semiconductor with high thermal conductivity. It is resistant to chemical etchants and radiation. It has high mechanical strength and biocompatible. SiC is the only Group IV compound semiconductor. And finally one of its polytypes, cubic silicon carbide (3C-SiC), can be grown on Si. There are over 200 polytpes of SiC. All of them are formed from 50% Si and C and consist of hexagonal SiC bilayers. Different stacking sequences of C-Si bilayers produces different crystal structures. Different polytypes have different properties and challenges. Due to this epitaxy is very challenging. Among all known polytypes only 3C-, 4H- and 6H- have been very well researched. Hexagonal polytypes of SiC such as 4H- and 6H-SiC already have commercial applications in power electronics and also used as substrates for gallium nitride (GaN). SiC substrates can be formed from these two polytypes, which can then be used for homoepitaxial growth at high temperatures for device applications. These substrates are extremely expensive, limited to 150 mm diameters and epitaxial growth requires very high temperatures (~1700-1800 °C), which are only achievable in specially designed, hot-walled chemical vapor deposition (CVD) reactors. 3C-SiC is the only polytype of SiC which possesses a zinc-blende crystal structure and can be grown on a Si substrate, below the Si melting point (1410 °C). Epitaxy state of the art and challenges for these polytypes and their application will be reviewed.