2.1 GaAs Based Metal Semiconductor FETs

At the moment, GaAs MESFETs are standard devices in ourdays industrial III-V production lines. On typically 6 inch substrates [316], they still cover a large amount of the overall III-V semiconductor production. Though increasingly challenged by III-V HBTs and HEMTs, they are easy to manufacture and cost effective. A number of processes such as [34,171] have been continuously optimized and been used in a great variety of circuit applications. Even with respect to high-speed there is a small number of reports with current gain cut-off frequencies ${\it f}_\mathrm{T}$ up to 100 GHz, e.g. by NTT in [198].