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.

Synchrotron White-Beam X-Ray Topography Analysis of the Defect Structure of HVPE-GaN Substrates

“…Single and groups of TSDs might act as sources for breakdown degradation in GaN-based high-power electronic devices as was observed for SiC. 22 From the viewpoint of crystal growth, these X-ray analyses show that the HVPE growth method has the potential to produce low-dislocation GaN crystals with dislocation densities in the range of ∼10 4 cm −2 and below. A prerequisite for this are GaN-seed crystals with correspondingly low defect density as the ammonothermal GaN material used here.…”

Bulk Growth and Characterization of SiC Single Crystal

“…Although the elementary screw dislocations did not seriously deteriorate the performance of device as micropipes, they prevent the realization of high-efficiency, reliable electronic devices (Lendenmann, 2001;Malhan et al, 2003;Neudeck et al, 1998). In order to assess the density of elementary screw dislocation, back-reflection synchrotron radiation topograph of (0001) wafer was taken.…”

Defect analysis in crystals using X‐ray topography

“…Direct comparisons can be drawn between the performance of specific devices and the distribution of defects within their active regions. This has made it possible to determine the influence of threading screw dislocations (closed and hollow-core) on device performance (Neudeck et al, 1998(Neudeck et al, , 2000. The back-reflection geometry is particularly useful here, since it gives a clear image of the distribution of screw dislocations on the background-device topology, which is imaged with sufficient clarity to unambiguously identify the device.…”