Effects of nitrogen on the interface density of states distribution in 4H-SiC metal oxide semiconductor field effect transistors: Super-hyperfine interactions and near interface silicon vacancy energy levels

Abstract

The performance of silicon carbide (SiC)-based metal-oxide-semiconductor field-effect transistors (MOSFETs) is greatly enhanced by a post-oxidation anneal in NO. These anneals greatly improve effective channel mobilities and substantially decrease interface trap densities. In this work, we investigate the effect of NO anneals on the interface density of states through density functional theory (DFT) calculations and electrically detected magnetic resonance (EDMR) measurements. EDMR measurements on 4H-silicon carbide (4H-SiC) MOSFETs indicate that NO annealing substantially reduces the density of near interface SiC silicon vacancy centers: it results in a 30-fold reduction in the EDMR amplitude. The anneal also alters post-NO anneal resonance line shapes significantly. EDMR measurements exclusively sensitive to interface traps with near midgap energy levels have line shapes relatively unaffected by NO anneals, whereas the measurements sensitive to defects with energy levels more broadly distributed in the 4H-SiC bandgap are significantly altered by the anneals. Using DFT, we show that the observed change in EDMR linewidth and the correlation with energy levels can be explained by nitrogen atoms introduced by the NO annealing substituting into nearby carbon sites of silicon vacancy defects.

Computational study of first-row transition metals in monodoped 4H-SiC

“…In addition, our Si vacancy levels also appear closer to the band edges than prior jellium-based studies. Our Si vacancy levels are in close agreement with experimental levels, suggesting that the difference in cell size or DFT functional matters more than charge correction scheme for such systems [21,22,[26][27][28]. This observation may be crucial for future research into similar metal-doped semiconductors, whenever a choice may be required between charge correction schemes and lattice size and relaxation, or when selecting between an LDA or GGA-PBE implementation of DFT.…”

“…Our results agree with prior LMCC studies on the similarly structured hexagonal polytype 2H-SiC, which place the −1/−2 acceptor level closer to the conduction band edge [21]. For the Si vacancy and Cr defects, our results for the previously studied metals have less absolute error when compared with experimentally attributed defect levels, and what error does exist tends to place these levels closer to the band edges rather than deeper into the gap [11,12,19,21,22,24]. The notable exception is vanadium, for which we find the acceptor to be an even deeper level than previously calculated and the donor to be a shallower level.…”

“…For the Si vacancy, we find one donor and one acceptor level near the valence band, and two acceptor levels near the conduction band. Our results agree with prior LMCC studies on the similarly structured hexagonal polytype 2H-SiC, which place the −1/−2 acceptor level closer to the conduction band edge [21]. For the Si vacancy and Cr defects, our results for the previously studied metals have less absolute error when compared with experimentally attributed defect levels, and what error does exist tends to place these levels closer to the band edges rather than deeper into the gap [11,12,19,21,22,24].…”

“…We find both donors and acceptors for each defect, with multiple acceptor states for all but V and single donor states for all but Mn. The number of in-gap defect states, order of charge transitions, spin polarization, and general area in the gap match well with prior studies [19,21,22]. Using these results on known defects as a basis for the accuracy of our calculations, we discuss the role of Fe, Co, and Ni on the electronic properties of 4H-SiC.…”

“…With no spurious delocalization, the physics does not require HSE or other exact exchange and self-interaction corrections schemes. Thus, we find that using a total energy method and conventional DFT functionals (GGA/PBE in our case) allows us to more efficiently explore defects across the periodic table without sacrificing the most important physics for the system under study [19,21,22,[32][33][34].…”