An investigation of different stress-free passivation layer designs in GaN HEMTs

Different stress-free silicon nitride passivation layer designs were simulated using simulation software Silvaco. Different SiNx passivation layer designs (passivation only between the gate-source and gate-drain, passivation edge exactly touching the edges of source and drain contacts and coming over the gate, passivation edges partially covering the source and drain contacts and completely covering the gate, passivation only in the channel area and completely covering the gate) were checked to study their role in GaN HEMTs device improvement process. Resulted Drain current (Ids) was recorded to be the same in all the different designs. A comparatively lower value of transconductance (gm) was observed in the design having passivation layer exactly touching the edges of source and drain contacts and coming over the gate. Therefore this design was not recommendable. Devices suffered with high gate leakage current independent of design types. An introduction of traps in AlGaN layer surprisingly reduced the gate leakage current in such structures.