Study of bulk and elementary screw dislocation assisted reverse breakdown in low-voltage (<250 V) 4H-SiC p+n junction diodes -: Part I:: DC properties

Given the high-density (similar to 10(4) cm(-2)) of elementary screw dislocations (Burgers vector = Ic with no hollow core) in commercial SIC wafers and epilayers, all large current (>1 A) SIC power devices will likely contain elementary screw dislocations for the foreseeable future. It is therefore important to ascertain the electrical impact of these defects, particularly in high-field vertical power device topologies where SiC is expected to enable large performance improvements in solid-state high-power systems, This paper compares the de-measured reverse-breakdown characteristics of low-voltage (<250 V) small-area (<5 x 10(-4) cm(2)) 4H-SiC p(+)n diodes with and without elementary screw dislocations. Diodes containing elementary screw dislocations exhibited higher pre-breakdown reverse leakage currents, softer reverse breakdown current-voltage (I-V) knees, and highly localized microplasmic breakdown current filaments compared to screw dislocation-free devices. The observed localized 4H-SiC breakdown parallels microplasmic breakdown observed in silicon and other semiconductors, in which space-charge effects limit current conduction through the local microplasma as reverse bias is increased.