Materials Science and Engineering Graduate Seminar

October 17, 2017

October 17, 2017

Speaker: Balaji Raghothamachar, Ph.D.
                 Stony Brook University  
Title: Application of X-ray Topography to Understanding Defect Behavior in Wide Bandgap Semiconductors 
Time: 12:10 pm

Abstract: X-ray topography is a powerful, non-destructive imaging technique capable of providing information on the nature and distribution of structural defects such as dislocations, inclusions, stacking faults, grain boundaries, etc. in single crystal materials. Over the past several decades, X-ray topography techniques have been widely used for the development of crystal growth techniques and applications of semiconductors, oxides, metals, proteins and other inorganic and organic materials. In this presentation, the application of X-ray topography using the powerful synchrotron radiation beam for the study and development of wide band gap (WBG) semiconductors for power electronics will be demonstrated. Among the wide bandgap semiconductors, silicon carbide (SiC) is the most promising semiconductor for efficient and reliable electrical energy conversion and power management. The physical vapor transport (PVT) method is used for bulk single crystal growth of SiC while chemical vapor deposition (CVD) is used for homoepitaxial growth of active device layers. Crystal defects such as micropipes, screw and edge dislocations, and stacking faults in substrates and epilayers prevent the development of cost-effective and reliable high-voltage SiC power devices. Continued reduction in defect content relies on analysis of defect configurations and correlation with growth processes and thermal modeling to optimize the growth process. In this presentation, a comprehensive overview will be presented of PVT growth of bulk SiC and CVD growth of SiC homoepitaxial layers with defect characterization by synchrotron X-ray topography. A complete analysis of the distribution, character and origins of grown-in c-axis screw dislocations, deformation induced basal plane dislocations (BPDs), grown-in threading edge dislocations and stacking fault formation in PVT-grown substrates will be discussed. In addition, dislocation behavior during homo-epitaxy on offcut substrates will be presented. Correlations with thermal modeling will be discussed. Insights from these analyses to achieve elimination of or minimizing specific defects will be demonstrated. Similar analysis of defect distributions in PVT-grown AlN as well as hydride vapor phase epitaxy (HVPE)-grown GaN and ammonothermal-grown GaN will also be presented.

Bio: Dr. Balaji Raghothamachar is a Senior Research Scientist and Research Professor in the Department of Materials Science & Chemical Engineering at Stony Brook University. His chief expertise is in the synchrotron topographic analysis of defects and generalized strain fields of single crystals in general, with particular emphasis on semiconductor, optoelectronic, and optical crystals, especially SiC, III-Nitrides, II-VI, sapphire and other related materials. Establishing the relationship between crystal growth conditions and resulting defect distributions is a particular thrust area of interest, as is the correlation between electronic/optoelectronic device performance and defect distribution. In-situ analysis of defect behavior during growth/processing/operation using synchrotron radiation is emphasized. Industrial collaborations are a particular strength with active research programs with Dow Corning, Saint Gobain, Hexatech, Fairfield Crystal, Cree, and other companies involved in crystal growth development. At Brookhaven National Laboratory (BNL), he served as Beamline Scientist from 2007 to 2014 at the Stony Brook Synchrotron Topography facility (beamline X-19C) at the National Synchrotron Light Source (NSLS). At BNL, he is also actively involved in user facility science outreach (ex-Chair of Users Executive Committee at Center for Functional Nanomaterials (CFN) and co-organizer of NSLS-II/CFN Annual Users’ Meeting). Member of AACG, MRS and ECS and co-organized symposiums at these conferences.

For more information, please contact Professor Deirdre O’Carroll at 848-445-1496 or at or Professor James Harrington at 848-445-3932 or at