Small current collapse in AlGaN/GaN HFETs on a-plane GaN self-standing substrate

We measured drain bias stress effects and current collapse in AlGaN/GaN heterostructure field-effect transistors (HFETs) on a-plane and c-plane GaN substrates. An a-plane AlGaN/GaN HFET (a-HFET) shows small current collapse with a threshold voltage (V-th=-1.8 V). On the other hand, a c-plane HFET (c-HFET) with the same barrier thickness (20 nm) shows a small current collapse, although V-th was negatively large (V-th=-4 V). Current collapse in a-HFET was not large compared with that in conventional c-HFET on GaN. A c-HFET on sapphire was also measured. The current collapses in HFETs on sapphire were larger than that in HFETs on a GaN substrate. The current collapses in the thin-barrier c-HFET (Vth=-1.8 V) were particularly large. Therefore, an a-plane device is promising for a small or positive Vth with small current collapse. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim