Influence of carrier supply doping on the RF properties of AlGaN/GaN/SiC high‐electron‐mobility transistors

Abstract

We have fabricated undoped as well as modulation-doped AlGaN/GaN HEMTs on SiC substrate. The influence of the carrier supply layer on device performance is investigated by Hall, channel conductivity, small signal RF and delay time evaluation. While the doping layer improves the DC performance it degrades the RF behaviour of the device with the highest carrier supply doping of 5x10 18 cm -3. The channel conductivity measurements show identical dependence of the mobility on carrier concentration for all samples. The saturation velocity, extracted by evaluation of the total delay time as function of the inverse drain current, decreases from 0.86x10 7 cm/s for the undoped device to 0.7x10 7 cm/s for the highest doped HEMT. This result shows that the degradation of RF performance is due to the reduction of the effective saturation velocity caused by the carrier supply layer.