Low field mobility in GaAs ion-implanted FET's

We describe a new technique which allows one to deduce the mobility profiles under the gate of an ion-implanted GaAs MESFET. The technique is based on the measurements of the transconductance and the series resistance at very low drain-to-source voltages. The experimental results show that the mobility drops to about 1000 cm²/V . s at the channel interface from its maximum value of about 2500 cm²/ V . s.