Electrically detected magnetic resonance study of barium and nitric oxide treatments of 4H-SiC metal-oxide-semiconductor field-effect transistors

We report on the effects of barium interfacial layer (IL) deposition and nitric oxide (NO) anneals on interface/near-interface defects in 4H-SiC metal-oxide-semiconductor field-effect transistors utilizing electrically detected magnetic resonance (EDMR). The 4H-SiC/SiO₂ interface has a large number of electrically active defects that reduce the effective channel mobility. Various passivation schemes have been utilized to decrease the interface defect density and thus increase mobility. Two passivation schemes of great interest are postoxidation annealing in nitric oxide (NO) and deposition of a barium interfacial layer (IL) before oxide growth. Our measurements compare the chemical nature of defects very near the 4H-SiC/SiO₂ interface in devices utilizing both passivation schemes and nonpassivated devices. Both the NO anneal and the barium IL greatly reduce the interface region EDMR response, which corresponds to a large improvement in mobility. However, the EDMR response in devices subjected to the two passivation processes is somewhat different. We present results that suggest spin lattice relaxation times are longer in samples that received a barium IL than in samples with NO annealing; this result suggests a lower level of local strain within the vicinity of defects very near the 4H-SiC/SiO₂ interface in barium treated samples over NO annealed samples.