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

Given the high-density (/spl sim/10/sup 4/ cm/sup -2/) of elementary screw dislocations (Burgers vector=1c 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 dc-measured reverse-breakdown characteristics of low-voltage (<250 V) small-area (<5/spl times/10/sup -4/ cm/sup 2/) 4H-SiC p/sup +/-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.