PERIMETER GOVERNED MINORITY-CARRIER LIFETIMES IN 4H-SIC P(+)N DIODES MEASURED BY REVERSE RECOVERY SWITCHING TRANSIENT ANALYSIS

Minority carrier lifetimes in epitaxial 4H-SiC p(+)n junction diodes w ere measured via an analysis of reverse recovery switching characteris tics. Behavior of reverse recovery storage time (t(s)) as a function o f initial ON-state forward current (I-F) and OFF-state reverse current (I-R) followed well-documented trends which have been observed for de cades in silicon p(+)n rectifiers. Average minority carrier (hole) lif etimes (tau(p)) calculated from plots of t(s) vs I-R/I-F strongly decr eased with decreasing device area. Bulk and perimeter components of av erage hole lifetimes were separated by plotting 1/tau(p) as a function of device perimeter-top area ratio (P/A). This plot reveals that peri meter recombination is dominant in these devices, whose areas are all less than 1 mm(2). The bulk minority carrier (hole) lifetime extracted from the 1/tau(p) vs P/A plot is approximately 0.7 mu s, well above t he 60 ns to 300 ns average lifetimes obtained when perimeter recombina tion effects are ignored in the analysis. Given the fact that there ha s been little previous investigation of bipolar diode and transistor p erformance as a function of perimeter-to-area ratio, this work raises the possibility that perimeter recombination may be partly responsible for poor effective minority carrier lifetimes and limited performance obtained in many previous SiC bipolar junction devices.