Synchrotron X-ray Topography Laboratory
Department of Materials Science & Engineering, Stony Brook University, Stony Brook, NY

Current Research Projects

An Investigation into the Properties of B12As2, B4C and their Heterostructures
National Science Foundation (NSF)

A joint research project between State University of New York at Stony Brook, Kansas State University and Bristol University to study the properties of the boron-rich icosahedral semiconductors, B12As2 and B4C, that lie at the extremes in many categories including high melting temperatures, hardness, resistance to radiation damage, and Seebeck coefficients. Enhancements of these properties may be realized by combining these materials together to create compositional heterostructures. The main objectives of this research are: (a) to develop process conditions capable of producing single and multiple thin layers combining both materials with controlled stoichiometry and impurity concentrations by chemical vapor deposition;

(b) to identify the types and density of crystalline defects present in both the bulk of the thin films and those caused by interfaces between materials; and (c) to investigate the electrical, optical, and thermal properties of base semiconductors and their composite structures. This study will establish the relationship between the processing, structure, composition, and properties of these boride semiconductors, so their potential applications as high temperature electronics, thermo electronics, radiation sensors and other devices may be realized.

Application of X-Ray Topography to the Study of Defects in Calcium Fluoride, EFG Sapphire and Other Crystals of Interest to St. Gobain
Saint Gobain Crystals

Saint-Gobain is a global leader in the manufacture and development of engineered materials such as glass, insulation, reinforcements, containers, building materials, ceramics and plastics. The Crystals Division is a world leader in the manufacture of ionizing radiation detection materials and photonic crystals. The Photonic Materials business consists of products to serve a wide variety of applications such as sapphire substrates for LED production and doped YAG crystals, ruby and Ti:Sapphire for solid state laser applications;

calcium fluoride for UV, visible and infrared transmission optics; sapphire by Edge-Defined Film Fed Growth for aerospace and defense applications as well as LED production. We are collaborating with various crystal growth facilities within the Saint Gobain Crystals division to optimize the single crystal growth process of these materials. Our contribution lies in characterizing defect distributions to improve the understanding of defect formation and devising growth strategies to eliminate them.

Mapping of package induced in-silicon stresses and assessment of processing-induced edge damage by x-ray topography
Intel Corporation

Integrated Circuits (ICs) for microelectronics are becoming more and more complex as technological developments demand higher performance and improved functionality from electronic circuits. They are used in ever more severe environmental conditions to answer to military, automotive or space needs. An electronic package serves as mechanical support and protection (from external environment such as high humidity level, light radiations, etc.) for the silicon chip and also allows power and signal transmission to and from the chip using interconnections from the chip surface to leads which extend outside the package.

This research proposal is broadly aimed at studying stresses and damage incurred in packaged silicon dies during the packaging process. These stresses and damage will be non-destructively and non-invasively measured as a function of lateral position and depth in the die using the techniques of Synchrotron White Beam X-ray Topography (SWBXT) and Synchrotron White Beam X-ray Reticulography (SWBXR) and 3D maps of the stress tensor will be generated.

SWBXT Studies of Grain Size, Orientation and Strain in Polysilicon Crystal Ingots, Bricks and Wafers
BP Solar International Incorporated

Solar energy technologies remain at the forefront of efforts to developing clean, reliable, renewable energy technologies. Improving solar cell efficiencies while holding down the cost per cell is an important goal of the PV industry, NREL researchers, and other U.S. Department of Energy (DOE) laboratories. Currently, solar cells based on silicon account for 98% of today's photovoltaic (PV) products that convert sunlight directly into electricity. The Crystalline Silicon Partnerships Team at NREL works with industry and university partners to develop novel approaches to produce high efficient, low-cost crystalline silicon cells, modules, materials, and processes. BP Solar is recognized as a global leader in providing solar energy solutions. This research project is funded under a NREL/DOE funded Photovoltaic Manufacturing Technology Program through BP Solar Inc.

The project is aimed at improving the efficiency of the multicrystalline silicon solar cell technology. Multicrystalline silicon is fast becoming the material of choice for silicon-based solar cells because of the low cost of production and comparable efficiency to monocrystalline silicon. We are collaborating with BP Solar to enhance understanding and enable improved control of the processing sequence used to convert high purity silicon chunk into multicrystalline solar cells. This processing sequence includes the casting process used in producing multicrystalline ingots, the band-sawing of the ingots into bricks, and the wire-sawing of the bricks into wafers.

UV-radiation assisted chemical vapor deposition of III-nitride functional nanostructures
National Science Foundation (NSF)

III-nitride materials (GaN, AlN, InN and their alloys) are wide band-gap semiconductors with important applications in the fabrication of UV and blue emitters, detectors, high-speed field-effect transistors (FETs), and high-power/high-temperature devices. Future enhanced electronic and photonic devices will demand the utilization of low-dimensional structures. Chemical vapor deposition (CVD) techniques have been successfully utilized to synthesize multiple kinds of nanomaterials. The synthesis process using standard thermal CVD techniques is mainly controlled by the temperature and mass transport conditions at the substrate surface where the heterogeneous chemical reaction takes place. Controlling the arrangement, nucleation, and growth of the resulting low dimensional structures remain as major challenges associated with CVD nanofabrication strategies.

This research is concerned with the development of novel synthesis strategies for III-nitride nanostructures using UV-radiation assisted CVD. By means of localized, selective excitation of chemical species and substrate surfaces using UV photons, the possibility for direct-writing and morphological control of III-nitride nanostructures will be determined. The synthesis experiments will be carried out utilizing a tunable UV beam-light (3.5-9eV) generated at the Brookhaven National Laboratory (BNL) National Synchrotron Light Source (NSLS). The chemical and structural characterization of the produced nanostructures will be carried out using SEM, EDAX, and HRTEM at both Stony Brook University and the BNLs Center for Functional Nanomaterials.

A Novel Growth Technique for Large Diameter AIN Single Crystal
Fairfield Crystal Technology LLC (DOE-SBIR)

Fairfield Crystal Technology is developing single crystal materials such as Aluminum Nitride (AlN) to be used as substrates for HB-LED's as part of a general effort for developing solid state inorganic and organic light emitting diodes for general lighting. Using Synchrotron White Beam X-ray Topography (SWBXT) and High Resolution X-ray Diffraction (HRXD), we carry out structural and microstructural characterization of

PVT-grown AlN single crystals in order to optimize the growth process and improve crystal quality. Other characterization techniques such as optical microscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), etc. are employed to complement and corroborate results from the x-ray techniques.