Plasma enhanced chemical vapor deposition of SiO2 and SiNx on AlGaN: Band offsets and interface studies as a function of Al composition

Abstract

In this work, the authors characterized the interface of plasma enhanced chemical vapor deposition (PECVD) dielectrics, SiO2 and SiNx with AlGaN as a function of Al composition. SiO2 is found to exhibit type I straddled band alignment with positive conduction and valence band offsets for all Al compositions. However, the interface Fermi level is found to be pinned within the bandgap, indicating a significant density of interface states. Hence, SiO2 is found to be suitable for insulating layers or electrical isolation on AlGaN with breakdown fields between 4.5 and 6.5 MV cm−1, but an additional passivating interlayer between SiO2 and AlGaN is necessary for passivation on Al-rich AlGaN. In contrast, Si-rich PECVD SiNx is found to exhibit type II staggered band alignment with positive conduction band offsets and negative valence band offsets for Al compositions <40% and type I straddled band alignment with negative conduction and valence band offsets for Al compositions >40% and is, hence, found to be unsuitable for insulating layers or electrical isolation on Al-rich AlGaN in general. In contrast to passivating stoichiometric LPCVD Si3N4, no evidence for interface state reduction by depositing SiNx on AlGaN is observed.