In-situ near-ambient-pressure photoelectron spectroscopy investigations of high-work-function MoO3 on 4H-SiC(0001)

Abstract

How to realize effective Ohmic contact to SiC represents one of the major challenges for high-power and high-frequency SiC electronics. Forming a high-work-function interfacial layer between metal electrode and semiconductor has been considered as a promising approach to realize effective Ohmic contact with wide bandgap semiconductors. In this work, a high-work-function (∼7.2 eV) interfacial molybdenum trioxide (MoO3) layer was grown on 4H-SiC(0001) using conventional vacuum thermal deposition process. We have also systematically investigated the evolution of surface properties of MoO3/4H-SiC(0001) via annealing under high vacuum and various gas environments (H2 and O2). The combination of in-situ near-ambient-pressure x-ray photoelectron spectroscopy (NAP-XPS) and ultra-high vacuum (UHV) ultraviolet photoelectron spectroscopy (UPS) investigations of the MoO3/4H-SiC(0001) reveal that the surface MoO3 tends to be reduced into Mo5+ and Mo4+ during annealing under UHV and 0.5 mbar H2. Most importantly, the surface work function of MoO3/4H-SiC(0001) was found to decrease accordingly together with the defect states originated from the transition from Mo+6 to Mo5+ and Mo4+. In contrast, the oxygen sites as well as its high work function are retained even after 400 °C annealing under 0.5 mbar O2, which indicates that the MoO3/4H-SiC(0001) interface is more thermally stable under oxygen treatment.