Carrier velocity in InAlN/AlN/GaN heterostructure field effect transistors on Fe-doped bulk GaN substrates

We report microwave characteristics of field effect transistors employing InAlN/AlN/GaN heterostructures grown on low-defect-density bulk Fe-doped GaN substrates. We achieved unity current gain cutoff frequencies of 14.3 and 23.7 GHz for devices with gate lengths of 1 and 0.65 μm, respectively. Measurements as a function of applied bias allow us to estimate the average carrier velocity in the channel to be ∼1.0×10⁷ cm/sec for a 1 μm device. Additionally, we found nearly no gate lag in the devices, which is considered a precondition for good performance under large signal operation.