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Fowler–Nordheim electron and hole tunneling characteristics across 4H-SiC MOS diodes are studied. Their slope constants are used to determine the hole effective mass in the thermal SiO2 and the 4H-SiC conduction band offset. The hole effective mass in the SiO2 is found to be 0.58 m, where m is the free electron mass. The 4H-SiC conduction band offset is found to be 2.78 eV. The average oxide fields used in the carrier tunneling characteristics are formulated. It is found that anode and cathode field corrections by the flatband voltage are critical in the evaluation of the above tunneling parameters.

We report the confirmed occurrence of Fowler–Nordheim hole tunneling in p-4H–SiC metal-oxide-semiconductor capacitor structures. The effective mass for holes in the oxide is found to be in the range of 0.35m–0.52m, where m is the free electron mass.

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Results of room temperature capacitance-voltage measurements are reported for SiO 2 /4H-SiC ͑n and p type͒ metal-oxide-semiconductor capacitors annealed in ammonia following oxide layer growth using standard wet oxidation techniques. For n-SiC capacitors, both the interface state density near the conduction band edge and the effective oxide charge are substantially reduced by the ammonia anneals. For 2 h anneals, the oxide charge appears to have a minimum value for an anneal temperature of approximately 1100°C. However, for p-SiC, anneals in ammonia produce no improvement in the interface state density near the valence band edge, and the effective oxide charge is not reduced compared to samples that were not annealed. Results are compared to those reported previously for anneals in nitric oxide. Ion beam analyses of the oxide layers show substantially more nitrogen incorporation with the ammonia anneals, although for n-SiC, the decrease in D it is comparable for both nitric oxide and ammonia anneals. Results reported here for ammonia and those reported previously for nitric oxide are the first to demonstrate that significant passivation of the interface state density near the conduction band edge in SiC can be achieved with high temperature anneals using either gas. This demonstration has important implications for SiC metal-oxide-semiconductor field effect transistor technology development.

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