InAlN has been investigated as barrier layer material for GaN -HEMT structures, potentially offering higher sheet charge densities [1] and higher breakdown fields [2]. Lattice matched growth of the barrier layer can be achieved with 17 % In content, avoiding piezo polarization. In this configuration the sheet charge density is only induced by spontaneous polarization. First experimental results of unpassivated undoped samples realized on 111- Si substrate exceed a DC output current density of 1.8 A/mm for a gate length of 0.5 μm. Small signal measurements yield a f t = 26 GHz and f max = 14 GHz , still limited by the residual conductivity of the Si -substrate. A saturated output power at 2 GHz in class A bias point yielded a density of 4.1 W/mm at V DS = 24 V .
