Advances in AlGaN/GaN HEMT Surface Passivation

The high efficiency and power density of AlGaN/GaN high electron mobility transistors (HEMTs) can be limited by parasitic charge trapping at sites on the semiconductor surface. Trapped electrons at the surface deplete the two-dimensional electron gas (2DEG), resulting in effects known as current collapse, increased dynamic on-resistance, DC-RF dispersion, among others. A plasma-enhanced chemical vapor deposition (PECVD) SiN layer is conventionally implemented as surface passivation for GaN HEMTs, however the properties of this SiN layer and the impact of this layer on current collapse depend drastically on the deposition conditions of this film. Although passivation of GaN HEMTs has been studied extensively, the specific details behind the SiN passivation deposition are not commonly provided within literature. In this work, we investigate several passivation PECVD SiN passivation schemes and study their performance under dynamic switching conditions, under off-state stress, and implement electroluminescence imaging to identify electric field nonunifornities.