In this paper, we present a normally-off GaN-based transistor with an extremely low on-resistance (R on) fabricated by using a Ge-doped n++-GaN layer for ohmic contacts. We developed a novel GaN regrowth technique using Ge as a dopant, which achieved an extremely high doping concentration of 1 × 1020 cm−3, and thereby the lowest specific contact resistance of 1.5 × 10−6 Ω·cm2. The NiO gate fabricated using an atomic layer deposition technique reduced the spacing between the source and drain electrodes. The fabricated device showed the record-breaking R on of 0.95 Ω·mm with the maximum drain current and transconductance of 1.1 A/mm and 490 mS/mm, respectively. Note that the obtained threshold voltage was 0.55 V. This extremely low R on characteristic indicates the great potential of NiO-gate GaN-based heterojunction field-effect transistors.

AbstractsIn this paper, we present a normally-off GaN-based transistor with extremely low on-state resistance fabricated by using Ge-doped n ++ GaN layer for ohmic contact. We developed a new GaN regrowth technique using Ge, which achieved extremely high doping level of 1 x 10 20 cm -3 , and thereby the lowest specific contact resistance of 1.5 x 10 -6 Ω·cm 2 . Selectively deposited NiO gate using Atomic Layer Deposition (ALD) technique contributed to shorten the spacing between source and drain, making normally-off characteristics even with the 30% Al mole fraction of AlGaN. The fabricated device showed the record-breaking R on of 0.95 Ω·mm with maximum drain current (I d,MAX ) and transconductance (g m ) of 1.1 A/mm and 490 mS/mm, respectively. It is noted that the obtained V th was 0.55 V. An on/off current ratio of 5 x 10 6 is also achieved.