Gate engineering in metal insulator semiconductor capacitors on native gallium nitride substrates for applications with high lifetime requirements

Planar metal-insulator-semiconductor capacitors are fabricated on native gallium nitride substrates with different gate dielectrics, namely, silicon dioxide, silicon nitride, and aluminum oxide. The leakage current was measured to determine their robustness regarding electrical breakdown. Hysteresis effects were evaluated for the different gate dielectrics and for the substrate and the epitaxial surface. A gate-first process with a gate contact made from poly-crystalline silicon was compared to a gate-last process with a sputtered aluminum gate. The former showed superior robustness against electrical breakdown with a dielectric breakdown field strength of ≈ 9 MV/cm, which was found to be mostly independent of temperature in the range of 250–450 K. Furthermore, gate oxide traps were estimated by means of stress/recovery gate current transient measurements to confirm field strength limits for high lifetime requirements. Based on the various measurements, silicon dioxide emerged as the best choice regarding breakdown robustness and hysteresis effects. A limit for the dielectric field strength of 3–4 MV/cm is proposed to avoid short- and long-term damage of the dielectric layer.