Breakdown Degradation Associated With Elementary Screw Dislocations In 4H-SiC P⁺N Junction Rectifiers

Abstract

It is well-known that SiC wafer quality deficiencies are delaying the realization of outstandingly superior 4H-SiC power electronics. While efforts to date have centered on eradicating micropipes (i.e., hollow core super-screw dislocations with Burgers vector > 2c), 4H-SiC wafers and epilayers also contain elementary screw dislocations (i.e., Burgers vector = 1c with no hollow core) in densities on the order of thousands per cm 2 , nearly 100-fold micropipe densities. This paper describes an initial study into the impact of elementary screw dislocations on the reverse-bias current-voltage (I-V) characteristics of 4H-SiC p + n diodes. First, Synchrotron White Beam X-ray Topography (SWBXT) was employed to map the exact locations of elementary screw dislocations within small-area 4H-SiC p + n mesa diodes. Then the high-field reverse leakage and breakdown properties of these diodes were subsequently characterized on a probing station outfitted with a dark box and video camera. Most devices without screw dislocations exhibited excellent characteristics, with no detectable leakage current prior to breakdown, a sharp breakdown I-V knee, and no visible concentration of breakdown current. In contrast devices that contained at least one elementary screw dislocation exhibited a 5% to 35% reduction in breakdown voltage, a softer breakdown I-V knee, and visible microplasmas in which highly localized breakdown current was concentrated. The locations of observed breakdown microplasmas corresponded exactly to the locations of elementary screw dislocations identified by SWBXT mapping. While not as detrimental to SiC device performance as micropipes, the undesirable breakdown characteristics of elementary screw dislocations could nevertheless adversely affect the performance and reliability of 4H-SiC power devices.

Characterization of a 15-μm cutoff HgCdTe detector array for astronomy

“…Pixels that exhibit trap-to-band tunneling in those devices may show a soft breakdown in the I-V curves, followed by the onset of trap-to-band tunneling. Similar behavior has been observed by other authors in 4H-SiC 25,26 and Silicon 27 diodes caused by screw dislocations and stacking faults respectively. The soft breakdown is caused by traps that become electrically active at a certain "threshold voltage".…”

“…The soft breakdown is caused by traps that become electrically active at a certain "threshold voltage". The soft breakdowns shown in Neudeck et al 25 and Ravi et al 27 were not uniform, and showed no correlation between the onset of the soft breakdown and the trap density since the traps associated with dislocations may have different threshold voltages at which they become electrically active. Bacon (2006) 5 introduced a variable trap density to parametrically fit the soft breakdown and is given by…”

Epitaxial Graphene

“…High-quality, high-purity 4H-and 6H-SiC commercial wafers are sawn and polished from boules that are grown by the physical vapor transport process. Defects found in SiC wafers are discussed by Neudeck [57]. Different orientations are also available; typical orientations are basal plane or slightly misoriented from the basal plane by an off cut (giving rise to a vicinal-like geometry) toward either the (1100) or (1 100) directions for various angles, e.g., 8 .…”

Effects of barrier height fluctuations and electron tunneling on the reverse characteristics of 6H–SiC Schottky contacts

“…Such filamentary behavior has already been observed in the context of highpower SiC p-i-n devices. 24,25 …”