On the speed and noise performance of direct ion-implanted GaAs MESFETs

Recent advances in high-speed and ultra-low-noise performance of GaAs MESFETs are reviewed. Experimental results showing that the current gain cutoff frequency and noise figure achieved by direct ion-implanted GaAs MESFETs are equal to or better than those achieved by GaAs HEMTs are presented. Detailed cryogenic-temperature microwave measurements of F/sub t/ on HEMTs and MESFETs are reported, showing a similar dependence of the effective velocity with temperature. It is concluded that the transport properties of the high electron mobility in the two-dimensional electron gas in HEMTs have been misinterpreted for high-speed device operation, and that the high-field velocity is the most important parameter for high-speed device operation. It is the fundamental Gamma -L valley separation of the material and the associated effectiveness, either GaAs or InGaAs, that limit the high-field velocity and thus the speed of the devices.>