Effect of GaN buffer thickness on the electrical properties of RF-MBE grown AlGaN/GaN HEMTs on free-standing GaN substrates

In this work we investigated the effect of varying the thickness of the UID GaN buffer, d_UID, on the electrical properties of AlGaN/GaN heterostructures and HEMTs. Seven heterostructures with 50 nm < d_UID < 500 nm were grown by RF-MBE on free-standing, semi-insulating HVPE-grown GaN substrates. Hall patterns, isolation test patterns, and HEMTs have been fabricated on these structures. We find that when d_UID < 200 nm, a wide range of electrical properties, including Hall mobility, sheet resistance, gate leakage, interdevice isolation, and output conductance degrade as the UID GaN buffer thickness is decreased.