High speed high power AlGaN/GaN heterostructure field effect transistors with improved ohmic contacts

Ti/Al/Ti/Au ohmic contacts with low contact resistance (as low as 0.24 Ω mm) were used in fabricating short gate length modulation-doped field effect transistors on MBE-grown AlGaN/GaN layers. Maximum drain current achieved was above 1 A/mm with a transconductance of 182 mS/mm. RF measurements showed a maximum f_τ of 35.9 GHz and an f_MAX of 57.0 GHz, both achieved with 0.15 μm gate length. Simple analysis showed an electron saturation velocity of 1.3×10⁷ cm/s in our device structure. Maximum gate-drain breakdown voltages for these devices were measured to be 30 to 35 V