When talking about resistance and materials, it's also important to note that silicon has relatively low optimal operating temperatures compared to some of the

When talking about resistance and materials, it's also important to note that silicon has relatively low optimal operating temperatures compared to some of the other semiconductors available. This limits the amount of voltage you can pump into it (because the resistance mean higher V leads to heat), and voltage correlates with clock frequency. GaN has already seen success in chargers, and silicon carbide is another promising material. We can't achieve the low level of defects needed for small process nodes yet, though. Disclaimer: I'm not a material scientist, so this is probably only partly correct.