Studies of c-Axis Threading Screw Dislocations in Hexagonal SiC
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Studies of c-Axis Threading Screw Dislocations in Hexagonal SiC Yi Chen1, Xianrong Huang2, Ning Zhang1, Govindhan Dhanaraj1, Edward Sanchez3, Michael F MacMillan3, and Michael Dudley1 1 Department of Materials Science and Engineering, Stony Brook University, Stony Brook, NY, 11794-2275 2 National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, NY, 117942275 3 Dow Corning Compound Semiconductor Solutions, Midland, MI, 48611 ABSTRACT In our study, closed-core threading screw dislocations and micropipes were studied using synchrotron x-ray topography of various geometries. The Burgers vector magnitude of TSDs can be quantitatively determined from their dimensions in back-reflection x-ray topography, based on ray-tracing simulation and this has been verified by the images of elementary TSDs. Dislocation senses of closed-core threading screw dislocations and micropipes can be revealed by grazing-incidence x-ray topography. The threading screw dislocations can be converted into Frank partial dislocations on the basal planes and this has been confirmed by transmission synchrotron x-ray topography. INTRODUCTION Devices made from silicon carbide (SiC) possess promising advantages in high temperature, high power and high frequency applications due to its unique combination of properties (e.g., high thermal conductivity, high breakdown voltage, chemical stability). However, various defects, e.g., closed-core threading screw dislocations (TSDs), micropipes (MPs), triangular defects (TDs), stacking faults (SFs) and low angle grain boundaries (LAGBs), can degrade the performance of SiC devices significantly. MP densities have recently been significantly lowered. However, TSDs remain in densities ranging from 103 - 104/cm2. TSDs in SiC are of great interest from several different points of view. First, it should be noted that TSDs play a critical role in maintaining the desired polytype promoting spiral step-flow growth. Second, they have been found to degrade device performance, reducing the breakdown voltage by 5-35% [1]. Third, the forest of TSDs in the as-grown crystal poses a significant barrier which creates a pinning effect on the glide of the basal plane dislocations (BPDs) either during growth or post-growth cooling, leading to localized higher densities concentration of BPDs. Fourth, TSDs have been found to interact with SFs in SiC epitaxial films expanding under forward bias, creating prismatic SFs [2]. EXPERIMENTAL SiC crystals used in the study are commercial 3-inch 4H-SiC wafers, grown by physical vapor transport (PVT) technique, with 8o off-cut towards [11-20]. Grazing-incidence topographs using the (11-28) plane reflections and back-reflection topographs using basal plane reflection were taken from the Si-face side.. A fine-scale copper grating with periodicity of 50 µm was
placed in the incident X-ray beam. The setting up in reticulography is similar and can be referred to Lang’s report.3 The imaging was carried out at the Stony Brook Synchrotron Topography Station, Beamline X-19
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