The electron mobility and free electron density have been measured in 4H– and 6H–SiC metal-oxide-semiconductor inversion layers using the Hall effect. The 4H–SiC inversion layers are found to have very poor conductance which is caused by severe trapping of electrons at the Si/SiO2 interface. The trapping causes reduced conductance through a reduction in the number of free electrons in the inversion layer, and also because of a drop in the mobility due to increased Coulombic scattering.
We have combined thermally stimulated-current (TSC) and capacitance–voltage (C–V) measurements to estimate oxide, interface, and effective border trap densities in 6–23 nm thermal, N2O, and N2O-nitrided oxides exposed to ionizing radiation or high-field electron injection. Defect densities depend strongly on oxide processing, but radiation exposure and moderate high-field stress lead to similar trapped hole peak thermal energy distributions (between ∼1.7 and ∼2.0 eV) for all processes. This suggests that similar defects dominate the oxide charge trapping properties in these devices. Radiation-induced hole and interface trap generation efficiencies (0.1%–1%) in the best N2O and N2O-nitrided oxides are comparable to the best radiation hardened oxides in the literature. After ∼10 Mrad(SiO2) x-ray irradiation or ∼10 mC/cm2 constant current Fowler–Nordheim injection, effective border trap densities as high as ∼5×1011 cm−2 are inferred from C–V hysteresis. These measurements suggest irradiation and high-field stress cause similar border trap energy distributions. In each case, even higher densities of compensating trapped electrons in the oxides (up to 2×1012 cm−2) are inferred from combined TSC and C–V measurements. These trapped electrons prevent conventional C–V methods from providing accurate estimates of the total oxide trap charge density in many irradiation or high-field stress studies. Fewer compensating electrons per trapped hole (∼26%±5%) are found for irradiation of N2O and N2O-nitrided oxides than for thermal oxides (∼46%±7%). More compensating electrons are also found for high-field electron injection than radiation exposure, emphasizing the significance of border traps to metal-oxide-semiconductor long term reliability. The primary effect of nitrogen on charge trapping in these oxides appears to be improvement of the near interfacial oxide in which border traps are found.
This work is a study of the formation mechanisms of interface traps (Nit) in metal-oxide-semiconductor devices. The time-dependence of the Nit formation has been measured as a function of oxide thickness following a short radiation pulse. The Nit formation time is found to increase as t2.6ox when the gate bias is negative during irradiation and positive afterward. This result is in excellent agreement with predictions of a hydrogen transport model where drift of hydrogen ions (H+) is the rate-limiting step. When the gate bias during irradiation is positive, interpretation of the correlation between data and model suggests that the hydrogen ions are preferentially created near the Si-SiO2 interface. Finally, the Nit formation time is found to decrease with increasing oxide field as E−1.73ox. This result is compatible with the hydrogen transport model if the average displacement per hop is assumed to be proportional to Em.
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