The effect of gate length variation on InAlGaN/GaN HFET device characteristics

InAlGaN/GaN heterostructure field effect transistors (HFETs) with a nearly lattice-matched barrier layer (thickness tbar = 8.3 nm) are investigated. The focus is set on resolving the systematic dependence of device characteristics on the gate length LG. Therefore, five different gate length devices with LG ranging from 75 nm to 2 µm have been realized. Peak values of 460 mS mm−1 and 100 GHz for transconductance gm and unity current gain cut-off frequency fT are obtained for the 75 nm device. DC characteristics as well as the cut-off frequency fT show systematic scaling with the gate length LG. Nevertheless, short-channel effects appear for the short gate length devices in both DC and RF operation, and a critical minimum aspect ratio LG/tbar of 27 is identified for the investigated barrier composition of xIn = 0.11; yAl = 0.63 and zGa = 0.26.