ON THE SPEED AND NOISE PERFORMANCE OF DIRECT ION-IMPLANTED GAAS-MESFETS

Direct ion-implanted GaAs MESFET's are the most attractive devices for microwave, millimeter-wave, and digital integrated circuit applications due to the affordability, availability, reliability, and manufacturability of ion implantation technology. This paper presents and reviews the recent advances in high-speed and ultra-low-noise performance of GaAs MESFET's. We present experimental results that the current gain cutoff frequency and noise figure achieved by direct ion-implanted GaAs MESFET's are equal to or better than those achieved by GaAs HEMT's. Furthermore, we have performed detailed cryogenic-temperature microwave measurements of F(t) on HEMT's and MESFET's and find a similar dependence of the effective velocity with temperature. We conclude that the transport properties of the high electron mobility in the two-dimensional electron gas in HEMT's have been misinterpreted for high-speed device operation, and 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 associated effectiveness, either GaAs or InGaAs, which limits the high-field velocity and thus speed of the devices.