Simulated I-V characteristics of non-uniformly doped microwave GaAs MESFET´s

To enhance the performance of a low-noise microwave GaAs MESFET an appropriate doping profile is required. The I-V characteristics of a microwave GaAs MESFETs with graded channel doping have been simulated by using a non-linear model. It has been shown that a device with a graded channel doping may give transconductance, g_m at least 4 times greater than the uniformly doped device. This shows a significant improvement in the value of g_m relative to a device having constant channel doping. Furthermore, a low value of Schottky barrier leakage current was also demonstrated by controlling the doping concentration at Schottky barrier interface. This result in improved low noise performance of the device, and a minimum noise figure less than 2 dB at 20 GHz may be attained in these devices. A conservative estimate shows that a 0.25 μm long and 4×25 μm wide GaAs MESFET, with graded channel doping, may exhibit unity gain frequency greater than 200 GHz. Thus, the proposed device structure could give a significant improvement in the exiting MESFET technology.