Impact of Fin Width on Tri-Gate GaN MOSHEMTs

Abstract

In this paper, we present a detailed investigation of the impact of fin width ( ${w}_{\text {fin}}$ ) on tri-gate AlGaN/GaN metal–oxide–semiconductor high electron mobility transistors (MOSHEMTs). As ${w}_{\text {fin}}$ is reduced, the threshold voltage ( ${V}_{\text {TH}}$ ) increases, which is due to the enhanced gate control (especially for ${w}_{\text {fin}} nm) thanks to the 3-D geometry of the tri-gate, and the reduced carrier concentration ( ${N}_{\text {s}}$ ) caused by a more pronounced strain relaxation and sidewall depletion, as explored using Hall and capacitance–voltage ( ${C}$ – ${V}$ ) measurements. Normally- OFF operation was achieved for ${w}_{\text {fin}}$ close to the sidewall depletion width ( ${w}_{\text {dep}}$ ) of 19.5 nm, since the fin is depleted from its two sidewalls. The impact of ${w}_{\text {fin}}$ on ON-resistance ( ${R} _{{{ {6{8} {\text {ON}}}}}}$ ) and current capability ( ${I} _{\text {D},\text {max}}$ ) was also investigated, along with the influence of the effective source injection, the trench conduction and the filling factor (FF) on these key characteristics. The degradation caused by the tri-gate fin etching could be fully recovered by increasing the FF. Finally, we show that the tri-gate can reduce gate capacitance ( ${C}_{\text {G}}$ ) and charge ( ${Q}_{\text {G}}$ ) in normally- ON MOSHEMTs, depending on the design of the tri-gate and the gate voltage ( ${V}_{\text {G}}$ ), leading to a smaller ${R}_{{{ {6{8} {\text {ON}}}}}} \cdot {Q}_{\text {G}}$ product that is beneficial for high-frequency switching applications. The results in this paper offer insights into important phenomena in tri-gate GaN devices and are fundamental for the further advance of this technology.