SiGe is a serious competitor to GaAs and InP. It doesn't typically have the power density of Ga derived microcircuits, but has good channel noise performance p

SiGe is a serious competitor to GaAs and InP. It doesn't typically have the power density of Ga derived microcircuits, but has good channel noise performance plus linearity and can operate at higher frequencies than GaAs as long as you don't need high power density. GaN has amazing power characteristics but has all kinds of issues with signal purity that are still being worked out. Eventually, I believe GaN will eat everything's RF lunch just out of sheer power efficiency gains with the last hold out being cell tower base stations, where spectral purity trumps efficiency by a mile. InP gets used into the 100GHz+ territory. These processes are mostly larger like you say, but they are also used in high end data converters (ADCs and DACs) and some processes are in the mid to low 10's of nanometers now. Which is almost exactly where silicon was a decade ago. Silicon of course isn't used because of it's performance, but rather, because silicon is the easiest of the semi-conductors to manufacture and get good yields out of. It is also comparatively very low cost. These factors have led to the lion's share of research dollars being spent there as well.