Probably not for the diode properties, but the transistor properties. I'm not an expert in this field, but some quick googling says GaN transistors (compared to

Probably not for the diode properties, but the transistor properties. I'm not an expert in this field, but some quick googling says GaN transistors (compared to silicon) have faster switching speeds and lower on-state resistance. I'm sure there's other tradeoffs, but those are great properties for high power, high frequency circuits.