Insight into the suppression mechanism of bulk traps in Al2O3 gate dielectric and its effect on threshold voltage instability in Al2O3/AlGaN/GaN metal-oxide-semiconductor high electron mobility transistors

Abstract

Bulk trapping and its effects on threshold voltage hysteresis (ΔVTH) in Al2O3/AlGaN/GaN metal–oxide-semiconductor high electron mobility transistors (MOS-HEMTs) have been identified by a combination of isothermal capacitance transient spectroscopy (ITS) and X-ray photoelectron spectroscopy (XPS). A post deposition annealing (PDA) at 500 °C in O2 ambient is confirmed to be an effective way to reduce the bulk traps in an atomic layer deposited (ALD)-Al2O3 film as it contributes to the suppressed ΔVTH in Al2O3/AlGaN/GaN MOS-HEMTs. The interface and bulk trapping behavior that account for ΔVTH, have been distinguished by ITS. It is revealed that continual charging of bulk traps in the Al2O3 gate dielectric occurred once the gate bias of the MOS-HEMTs is applied exceeding +3 V, which leads to the degraded ΔVTH as well as subthreshold slopes in transfer characterization. Such bulk traps probably stem from the Al-O-H component in the as-deposited Al2O3 layers, as detected by XPS. Energy band simulation further illustrates the capture process of the bulk traps, verifying the physical relationship between bulk-trapping and ΔVTH in GaN-based MOS-HEMTs.