Controlled oxide interlayer for improving reliability of sio2/gan mos devices

Abstract

Gallium nitride (GaN) has attracted considerable attention for use in future power-switching devices because its physical characteristics are superior to those of Si. The wide bandgap and high-breakdown electric field of GaN allow power devices to be made that are capable of high-temperature operation and low on-resistance.1-4) After successful commercialization of lateral AlGaN/GaN heterojunction fieldeffect transistors (HFETs),5-8) vertical power devices have been intensively investigated.9-12) Similarly to vertical Si and silicon carbide (SiC) power devices, normally-off switching devices such as GaN-based metal-oxide-semiconductor fieldeffect transistors (MOSFETs) are highly required in fail-safe systems. As for the gate insulators in GaN power devices, deposited dielectric films with sufficiently large band offset against the GaN-based semiconductors, such as Al2O3, SiO2, and their oxynitrides, can be possible candidates for limiting the gate leakage current.13-24) Actually, these wide bandgap insulators have been used in recent development of AlGaN/GaN MOS-HFETs; advanced deposition techniques, postdeposition annealing, and their combinations have been investigated by many researchers. While the two-dimensional electron gas in AlGaN/GaN MOS-HFETs is separated from the insulator/semiconductor interface with the AlGaN barrier layer, inversion carriers in the GaN MOSFETs are directly accumulated at the interface. This indicates that the quality of the interface between the deposited gate dielectric films and GaN substrates is crucial for good performance and high reliability of GaN MOSFETs.