Practical considerations when comparing SiC and GaN in power applications

Silicon Carbide (SiC) and Gallium Nitride (GaN) semiconductor technologies are promising great things for the future. SiC devices in a cascode configuration enable existing systems to be easily upgraded to get the benefits of wide band-gap devices right now. Wide band-gap devices – what they promise Wide band-gap (WBG) semiconductor technologies such as Silicon Carbide (SiC) and Gallium Nitride (GaN) are the hot topics of the moment, promising anything from universal wireless charging to power converters shrunk to almost no size. However, the choice between the technologies and devices available is not always straightforward, and the markets they can penetrate are perhaps wider than you might think. Let’s take a step back and just outline what WBG devices are. Semiconductors have bound electrons that occupy distinct energy levels around an atomic nucleus – valence and conduction bands. Electrons can move up to the conduction band and be available for current flow, but require energy to do so. In WBG devices this energy requirement is much greater than with silicon (Si). For example, SiC requires 3.2 electron-volts (eV) compared with Si at 1.1eV. The increased energy required to move electrons in WBG devices into the conduction band translates to higher electric field breakdown performance compared with Si of the same scale. For the same reason, SiC can withstand higher temperatures (thermal energy) before failure and also, as a material, has a thermal conductivity about 3.5 times better than Si. In practice these attributes promise high-frequency, high-temperature operation at high voltage and power levels. Devices initially available in SiC were simple diodes, but the material technology has advanced to enable fabrication of JFETs and MOSFETs. Figure 1 shows a cell of a SiC JFET with a vertical trench construction giving very low ON-resistance, compared with a GaN High Electron Mobility Transistor (HEMT) cell with lateral construction.