5-7-1 Future Tied to Material Issues
The previous sections of this chapter have already highlighted major known technical obstacles and immaturities that are largely responsible for hindered SiC device capability. In the most general terms, these obstacles boil down to a handful of key fundamental material issues. The rate at which the most critical of these fundamental issues is solved will greatly impact the availability, capability, and usefulness of SiC semiconductor electronics. Therefore, the future of SiC electronics is linked to investment in basic material research toward solving challenging material-related impediments to SiC device performance, yield, and reliability.
The material challenge that is arguably the biggest key to the future of SiC is the removal of dislocations from SiC wafers. As described previously in this chapter and references therein, the most important SiC power rectifier performance metrics, including device ratings, reliability, and cost are inescapably impacted by high dislocation densities present in commercial SiC wafers and epilayers. If mass-produced SiC wafer quality approached that of silicon wafers (which typically contain less than one dislocation defect per square centimeter), far more capable SiC unipolar and bipolar high-power rectifiers (including devices with kilovolt and kiloampere ratings) would rapidly become widely available for beneficial use in a far larger variety of high-power applications. Similar improvements would also be realized in SiC transistors, paving the way for SiC high-power devices to indeed beneficially displace silicon-based power devices in a tremendously broad and useful array of applications and systems (Section 5.3). This advancement would unlock a much more rapid and broad SiC-enabled power electronic systems “revolution” compared to the relatively slower “evolution” and niche-market insertion that has occurred since SiC wafers were first commercialized roughly 15 years ago. As mentioned in Section 5.4, recent laboratory results indicate that drastic reductions in SiC wafer dislocations are possible using radically new approaches to SiC wafer growth compared to standard boule-growth techniques practiced by all commercial SiC wafer vendors for over a decade. Arguably, the ultimate future of SiC high-power devices may hinge on the development and practical commercialization of low dislocation density SiC growth techniques substantially different from those employed today.
It is important to note that other emerging wide bandgap semiconductors besides SiC theoretically offer similarly large electrical system benefits over silicon semiconductor technology as described in Section 5.3. For example, diamond and some Group III-nitride compound semiconductors (such as GaN; Table 5.1) have high breakdown field and low intrinsic carrier concentration that enables operation at power densities, frequencies, and temperatures comparable to or exceeding SiC. Like SiC, however, electrical devices in these semiconductors are also hindered by a variety of difficult material challenges that must be overcome in order for beneficially high performance to be reliably achieved and commercialized. If SiC electronics capability expansion evolves too slowly compared to other wide bandgap semiconductors, the possibility exists that the latter will capture applications and markets originally envisioned for SiC. However, if SiC succeeds in being the first to offer reliable and cost-effective wide bandgap capability to a particular application, subsequent wide-bandgap technologies would probably need to achieve far better cost/performance metrics in order to displace SiC. It is therefore likely that SiC, to some degree, will continue its evolution toward expanding the operational envelope of semiconductor electronics capability.