High Power Density ScAlN-Based Heterostructure FETs for mm-Wave Applications

We report on recent progress on the development of Scandium Aluminum Nitride (ScAlN) based heterostructure field effect transistors (HFETs). We are leveraging the enhanced polarization properties of ScAlN lattice-matched to Gallium Nitride (GaN) to produce heterostructures that support very large carrier densities (>3.0 × 10¹³ /cm²). We have successfully grown device-quality ScAlN/GaN heterostructures by molecular beam epitaxy (MBE). Using these wafers we have fabricated low resistance contacts for ScAlN barrier HFETs and demonstrated transistors which simultaneously achieve high current density (>3 A/mm), large breakdown voltage (>60 V), and good mm-wave small signal gain (>13 dB at 30 GHz). The high current density coupled with the large breakdown field strength of GaN enables both current and voltage scaling of ScAlN/GaN HFETs and enables design of transistors that overcome the Bode-Fano bandwidth limitations.