Characterization of power MESFETs on 4H-SiC conductive and semi-insulating wafers

We report on the characterization of MESFETs designed for L and S-band power amplification and processed on 4H-SiC conductive (n+) and semi-insulating wafers. Both exhibit promising DC characteristics (I-dss = 300mA/mm; BVds > 150V). As expected, the microwave small signal performance is much better on semi-insulating substrates (f(t) = 6 GHz, f(max) = 20 GHz) than on conductive ones (f(t) = 4 GHz and f(max) = 10 GHz). Unfortunately, for devices on semi-insulating substrates, the drain current continuously decreases with time under DC bias conditions. As a consequence, the RF high power performance is still modest (P-out = 3 W at 2 GHz for a 6mm periphery transistor), even lower than on conductive substrates (Pout = 1,7 W on a 1 mm periphery transistor). Traps, whose location in the bandgap is not clearly identified yet, are probably responsible for this phenomenon. High-temperature I(V) and storage characterization of MESFETs processed on conductive substrates have been performed, showing good behavior in the conditions of the experiments.