Density of interface states, electron traps, and hole traps as a function of the nitrogen density in SiO 2 on SiCInterfaces between 4H-SiC and Si O 2 : Microstructure, nanochemistry, and near-interface traps J. Appl. Phys. 97, 034302 (2005); 10.1063/1.1836004 Study on electron trapping and interface states of various gate dielectric materials in 4H-SiC metal-oxidesemiconductor capacitors Electron states at the SiO 2 / 4H -SiC interface have been investigated using capacitor structures and especially, the influence of excess nitrogen, introduced by ion implantation, at the interface is studied in detail. Implanted and nonimplanted n-type samples with an interfacial concentration of nitrogen of ϳ10 19 cm −3 and 10 16 cm −3 , respectively, were analyzed by capacitance-voltage ͑C-V͒ measurements, performed at different temperatures and probe frequencies, and thermal dielectric relaxation current ͑TDRC͒ measurements performed in the temperature range of 35-295 K. Three main categories of electron states are disclosed, true interface states ͑D it ͒, fast near interface states ͑NIT ox fast ͒ and slow near interface states ͑NIT ox slow ͒. The density versus energy distributions of D it and NIT ox fast have been deduced from the TDRC data and they are shown to give a close quantitative agreement with the shape and frequency dependence of the C-V curves. Further, the amount of NIT ox slow extracted from TDRC is demonstrated to be responsible for the parallel shifts and hysterezis effects occurring in the C-V characteristics. All three categories of electron states are reduced in concentration in the implanted samples. This holds particularly for NIT ox fast with a peak at ϳ0.1 eV below the conduction band edge of 4H-SiC that is suppressed by at least two orders of magnitude relative to the nonimplanted samples. The decrease for D it is also substantial ͑a factor of ϳ10͒ while the loss for NIT ox slow is considerably smaller ͑only ϳ30%͒. The results provide firm evidence that NIT ox fast and NIT ox slow do not originate from the same kind of defect center.