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Instruments / Technical Area	Publication Details	Published
B16-Test Beamline	Analysis of basal plane dislocation dynamics in PVT-grown 4H-SiC crystals during high temperature treatment Balaji Raghothamachar , Yu Yang , Jianqiu Guo , Michael Dudley Ecs Transactions 92, 131 - 139 236th ECS Meeting DOI: 10.1149/09207.0131ecst Diamond Proposal Number(s): [13464] Show Abstract ▼ Abstract: Fundamental understanding of the generation and multiplication of basal plane dislocations (BPDs) in PVT-grown 4H-SiC crystals is critical for design of growth strategies to control their densities during PVT growth of 4H-SiC crystals. Direct observation of thermal gradient induced motion of basal plane dislocations by in-situ synchrotron X-ray topography imaging of PVT-grown 4H-SiC wafers subject to high temperature treatment has provided an opportunity to analyze the movement of dislocations. Dislocations with Burgers vector along the off-cut [11-20] direction were found to be the only dislocations involved in deformation during heat treatment and the segments of dislocations used for velocity measurements were found to be either pure screw comprised of both Si- and C- core partials or 60° dislocations comprised of purely Si cores. Using the kink-diffusion model, the activation energies for dislocation motion have been estimated from the velocity data for each of these dislocation types and found to be 2.21 eV for 60° and 3.28 eV for pure screw segments, respectively. These values are in good agreement with the macroscopic studies of yielding of semiconductor crystals during high temperature compression and indentation experiments. Quantitative expression of the temperature dependent critical resolved shear stress required for dislocation motion has been derived from this analysis.	Oct 2019
B16-Test Beamline	In situ synchrotron x-ray topography observation of double-ended Yu Yang , Jian Qiu Guo , Balaji Raghothamachar , Michael Dudley , Swetlana Weit , Andreas N. Danilewsky , Patrick J. Mcnally , Brian K. Tanner Materials Science Forum 924, 172 - 175 DOI: 10.4028/www.scientific.net/MSF.924.172 Diamond Proposal Number(s): [13464] Show Abstract ▼ Abstract: We present in-situ observations of the dynamical operation of multiple double-ended Frank-Read dislocation sources in a PVT-grown 4H-SiC wafer under thermal gradient stresses. The nucleation of these sources is facilitated by a specific configuration consisting of one basal plane dislocation (BPD) segment pinned by two threading edge dislocations (TEDs). This configuration is formed during PVT crystal growth by deflection of TEDs on to the basal planes by macrosteps and re-deflection of resulting BPDs back into TEDs. Under the influence of thermal gradient stresses induced by heating inside a double ellipsoidal mirror furnace, the pinned BPD segment glides and activates dislocation multiplication by the double Frank-Read source mechanism. A more intricate mechanism of swapping of TED pinning points between Frank-Read sources lying on the same basal plane is identified, enabling one dislocation loop to effectively “pass through” the other dislocations on the same basal plane.	Jun 2018
B16-Test Beamline	In-situ synchrotron x-ray topography study on the stress relaxation process in 4h-sic homoepitaxial layers Jianqiu Guo , Tuerxun Ailihumaer , Hongyu Peng , Balaji Raghothamachar , Michael Dudley Ecs Transactions 86, 75 - 82 DOI: 10.1149/08612.0075ecst Diamond Proposal Number(s): [13464] Show Abstract ▼ Abstract: During 4H silicon carbide (4H-SiC) homoepitaxy and post-growth processes, the development of stress relaxation has been observed, in which interfacial dislocations (IDs) are formed at the epilayer/substrate interface, relaxing the misfit strain induced by the nitrogen doping concentration difference between the epilayer and substrate. It is widely believed that an interfacial dislocation is created by the glide of a mobile segment of a basal plane dislocation (BPD) in the substrate or epilayer towards the interface, leaving a trailing edge component right at the interface. However, direct observation of such mechanisms has not been made in SiC before. In this work, we present an in situ study of the stress relaxation process, in which a specimen cut from a commercial 4H-SiC homoepitaxial wafer undergoes the stress relaxation process during a high-temperature heat treatment while sequential synchrotron white beam X-ray topographs were recorded simultaneously. Based on the dynamic observation of this process, it can be concluded that thermal stress plays a role in the relaxation process while the increased misfit strain at elevated temperature most likely drives the formation of an interfacial dislocation.	Sep 2018

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