Vertical GaN-on-GaN finFETs: Effect of SiN$_{x}$ Spacer Layer on Breakdown Voltage and Device Stability Under Gate Bias Stress

The effect of a SiNxspacer layer on the performance and reliability of vertical gallium nitride (GaN)-based fin field-effect-transistors (finFETs) is investigated. Inclusion of the SiNxspacer layer significantly enhancesoff-state characteristics by increasing breakdown voltage fromon-state performance. However, devices with SiNxspacer showed significant degradation in stability of device threshold voltage following bias stress in bothon- andoff-states, representing reduced device reliability. This is attributed to defects in the Al2O3gate dielectric layer associated with the SiNxspace layer deposition process, specifically a defect reservoir of density N${}_{\text {ot}} \gt 10^{{19}}$cm${}^{-{3}}$extending >4 nm into the gate dielectric layer according to a tunneling-front model. The performance-reliability tradeoff highlights that future fabrication methods must minimize processing damage to ensure both high-voltage capability and long-term operational stability.