I. Introduction
In SILICON carbide, the carrier-generation rate is extremely low at room temperature. This is because silicon carbide is a wide energy gap material ( eV in 4H-SiC [1]) with very low intrinsic-carrier concentration ( cm∓3 in 4H-SiC [1]). Based on the Shockley–Read–Hall (SRH) theory [2], [3], the generation rate is proportional to , so the generation rate in SiC should be many orders of magnitude lower than in Si [1], [4]. With this low generation rate, it should be possible to minimize the leakage current of reverse-biased P-N junctions to the levels that enable unique applications. One of these applications relates to the development of nonvolatile random-access memories (NVRAMs). Characterizing an NVRAM cell, based on an N-P-N structure in 6H SiC, Wang et al. [5] concluded that surface generation at the junction terminations increased the carrier-generation rate well above the value that would be expected in the bulk of a high-quality SiC substrate. Recently, the passivation of SiC surfaces has been considerably improved by using nitrided thermal oxides [6], [7]. Using nitrided gate oxides, extremely long charge-retention times have been experimentally demonstrated for MOS capacitors on 4H SiC [8], [9] and 6H SiC [10].