INVESTIGATION WALK-OUT PHENOMENA IN SIC MESA DIODES WITH SIO2 SI3N4 PASSIVATION/

The drift or ''walk-out'' of the breakdown voltage in 6H-SiC mesa diod es passivated by a double layer of 1000 Angstrom SiO2 and 3000 Angstro m Si3N4 was investigated. The drift characteristics of diodes having w et and dry oxide passivation were compared to each other and to diodes subjected to additional hydrogen plasma etching of the SiC surface pr ior to dry oxidation. The influence of the UV illumination supplied by a HeCd laser of wavelength 325 nm on the walk-out characteristics and on the reverse current was investigated. No significant differences i n the amount of drift and saturation level of breakdown voltage was fo und between the different passivations. However, the saturation level was reached about one order of magnitude faster in the wet oxide. A si gnificant difference was found in the level and time dependence of the reverse current under UV illumination between the wet and dry oxide p assivated diodes. The results are consistent with the existence of lar ge concentrations of positive charge and acceptor-type deep interface traps. The walk-out is the result of the acceptor states being filled by hot electrons through the mechanism of avalanche injection. (C) 199 7 Elsevier Science S.A.