Processing and characterization of N-polar GaN/AlGaN HFETs grown on 200 mm sapphire substrates

Abstract

N-polar GaN heterostructure field-effect transistors (HFETs) promise performance and scaling advantages over conventional Ga-polar GaN-based devices for high-frequency applications. However, N-polar GaN epitaxy remains challenging and limited to smaller wafer diameters. In this work, N-polar HFET structures are grown using a production-type metal–organic chemical vapor deposition tool on 200 mm sapphire substrates. The resulting material exhibits high crystalline quality with a wavy surface and root mean square roughness of 6.5 nm for a 5 × 5 μm2 area. Fabricated HFETs passivated with plasma-enhanced chemical vapor deposited SiNX yield good Ohmic and Schottky contact properties, as well as two-dimensional electron gas carrier concentrations on the order of 1013 cm−2 and mobilities up to 1000 cm2/V s. Despite notable gate leakage currents, low DC–RF dispersion, and good small-signal performance with transit-frequency values up to 9 GHz for 1 μm long gates are achieved for the investigated HFETs.