GaAs for on-chip inductors

Maybe this is not an appropriate forum for this query, so I apologize. I was reading that GaAs is being used on-chip inductors, basically because of its high (as compared to Si) electron mobility. However, if one can have copper interconnects on a chip, why not use copper for on-chip inductors ? Could someone point me to a good reference on a GaAs on-chip inductors ? Thanks in advance.