MSM varactor diodes based on AlGaN/GaN/SiC HEMT layer structures

The influence of a carrier supply layer on the electrical properties of MSM diodes based on AIGaNIGaN HEMT layer structures is investigated. The voltage dependence of the Schottky contact capacitance allows the use of the device as varactor diode with CMAX! CMfN ratios up to 17, tuneable by contact geometry. The carrier supply doping determines the sheet carrier density of the twodimensional electron gas channel, which is responsible for the transition voltage and the series resistance of the MSM diode. A device based on the highest doped layer structure shows a cutofffrequency as high as 65 GHz.