Non-Micropipe Dislocations in 4H-SiC Devices: Electrical Properties and Device Technology Implications
- PDF / 1,325,247 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 67 Downloads / 234 Views
power devices cannot be realized at present. While small-current, small-area high-voltage (1-5 kV) SiC devices are being prototyped and tested, the high densities of crystallographic defects in SiC wafers prohibits the attainment of SiC devices with very high operating currents (> 50 A) that are commonly obtainable in silicon-based high-power electronics [ 1, 2]. Micropipe defects are clearly very detrimental to electrical device performance, as these defects cause premature breakdown point-failures in SiC high-field devices fabricated in 4H- and 6H-SiC c-axis crystals with and without epilayers [2]. Commercial 4H- and 6H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = lc with no hollow core) in densities on the order of thousands per cm 2, nearly 100-fold micropipe densities [3-6]. Because of the non-terminating behavior of screw dislocations, both hollow-core (micropipes) and non-hollow-core (elementary) screw dislocations and associated crystal lattice stresses are replicated in subsequently grown SiC epilayers [7, 8]. The electrical impact of elementary screw dislocation defects on SiC device performance has largely been overlooked while attention has focused on eradicating SiC micropipes. However, as SiC micropipe densities fall below 1 per cm 2 in the best reported wafers [9], the operational effects of elementary screw dislocations must now be considered. While not nearly as detrimental to SiC device performance as micropipes, it has recently been demonstrated that elementary screw dislocations somewhat degrade the reverse leakage and breakdown properties of 4H-SiC p~n diodes [10]. Diodes containing elementary screw dislocations exhibited a 5% to 35% reduction in breakdown voltage, higher pre-breakdown reverse leakage current, softer reverse breakdown I-V knee, and highly localized microplasmic breakdown current filaments. Localized breakdowns and high-current filaments at junction hotspots are undesirable in silicon-based solid-state power devices. In operational practice, silicon power devices that 107 Mat. Res. Soc. Symp. Proc. Vol. 512 ©1998 Materials Research Society
uniformly distribute breakdown current over the entire junction area exhibit much greater reliability than silicon devices that manifest localized breakdown behavior. This is because silicon devices that avoid localized junction breakdown exhibit larger Safe Operating Areas (SOA's) and can much better withstand repeated fast-switching stresses and transient overvoltage glitches that arise in high-power systems [11-14]. Positive temperature coefficient of breakdown voltage (PTCBV), a standard behavior in silicon power devices free of crystal dislocation defects, helps insure that current flow is distributed uniformly throughout a device, instead of concentrated at high-current filaments. This enables silicon power rectifiers to exhibit a high energy to thermal junction failure when subjected to transient breakdown or switching bias conditions in which voltage and current are simultaneously large
Data Loading...
