Dr. H. Walter Yao Profile

Dr. H. Walter Yao

SPIE Involvement:

Author

Proceedings Article | 21 October 2004 Paper

Large-size CdZnTe (Zn=10%) radiation detector materials and device performance

Longxia Li, Fengying Lu, Chun Lee, Marc Black, Ralph James, H. Walter Yao, Arnold Burger, Michael Groza, Richard Olsen, Leonard Cirignano, Donald Ouimette

Proceedings Volume 5540, (2004) https://doi.org/10.1117/12.566740

KEYWORDS: Sensors, Indium, Crystals, Sensor performance, Electronics, Cadmium, Lithium, Energy efficiency, Electrons, Spectroscopy

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Proceedings Article | 20 January 2004 Paper

New progress in large-size CZT single-crystal growth for nuclear radiation detectors

Longxia Li, Fengying Lu, Chun Lee, H. Walter Yao, Arnold Burger, M. Groza, G. Wright, Ralph James, Richard Olsen, Paul Luke, Kanai Shah, Leonard Cirignano, Michael Squillante, Donald Ouimette

Proceedings Volume 5198, (2004) https://doi.org/10.1117/12.507745

KEYWORDS: Cadmium, Crystals, Sensors, Indium, Doping, Lithium, Gamma radiation, Nuclear radiation, Semiconducting wafers, Sodium

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Proceedings Article | 18 December 2001 Paper

Tellurium antisites in CdZnTe

Muren Chu, Sevag Terterian, David Ting, Ralph James, Jay Erickson, H. Walter Yao, Terrance Lam, Marek Szawlowski, Richard Szczebiot

Proceedings Volume 4507, (2001) https://doi.org/10.1117/12.450755

KEYWORDS: Crystals, Tellurium, Cadmium, Sensors, Indium, Zinc, Doping, Electrons, Gamma radiation, Infrared radiation

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Proceedings Article | 21 November 2000 Paper

Characterization of CZT detectors grown from horizontal and vertical Bridgman

Haim Hermon, Michael Schieber, Mark Goorsky, Terrance Lam, Evgenie Meerson, H. Walter Yao, Jay Erickson, Ralph James

Proceedings Volume 4141, (2000) https://doi.org/10.1117/12.407580

KEYWORDS: Crystals, Sensors, Spectroscopy, X-rays, X-ray diffraction, X-ray detectors, Chlorine, Digital x-ray imaging, X-ray imaging, Single crystal X-ray diffraction

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Proceedings Article | 21 November 2000 Paper

Characterization of multi-element CZT arrays

Leonard Cirignano, Kanai Shah, Paul Bennett, Longxia Li, Fengying Lu, Joseph Buturlia, H. Walter Yao, Gomez Wright, Ralph James

Proceedings Volume 4141, (2000) https://doi.org/10.1117/12.407600

KEYWORDS: Sensors, Collimation, Multi-element lenses, Gamma radiation, Detector arrays, Chemical elements, Particles, Chlorine, Floods, X-rays

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Proceedings Article | 17 April 2000 Paper

Optical properties of AlN/sapphire grown at high and low temperatures studied by variable angle spectroscopic ellipsometry and micro Raman scattering

Chunhui Yan, H. Walter Yao, Amber Abare, Steven DenBaars, Jody Klaassen, M. Rosamond, Peter Chow, John Zavada

Proceedings Volume 3938, (2000) https://doi.org/10.1117/12.382820

KEYWORDS: Phonons, Sapphire, Raman scattering, Spectroscopic ellipsometry, High temperature raman spectroscopy, Raman spectroscopy, Reflection, Gallium nitride, Solids, Temperature metrology

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Proceedings Article | 19 October 1999 Paper

Development of IMARAD CZT detectors with PIN contacts

Tomohiko Narita, Peter Bloser, Jonathan Grindlay, Jonathan Jenkins, H. Walter Yao

Proceedings Volume 3768, (1999) https://doi.org/10.1117/12.366627

KEYWORDS: Sensors, Crystals, Electric field sensors, Gold, Indium, Energy efficiency, Imaging systems, Hard x-rays, Image resolution, Cadmium sulfide

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Proceedings Article | 19 October 1999 Paper

Optical engineering and characterization of the internal electric field of CdZnTe radiation detectors

H. Walter Yao, Ralph James, Jay Erickson

Proceedings Volume 3768, (1999) https://doi.org/10.1117/12.366598

KEYWORDS: Sensors, Electric field sensors, Semiconductors, Optical engineering, Electrons, Infrared sensors, Infrared radiation, Photon polarization, Transmittance, Electro optics

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Proceedings Article | 14 April 1999 Paper

Optical anisotropy of GaN/sapphire studied by generalized ellipsometry and Raman scattering

Chunhui Yan, H. Walter Yao, James Van Hove, Andrew Wowchak, Peter Chow, John Zavada

Proceedings Volume 3621, (1999) https://doi.org/10.1117/12.344490

KEYWORDS: Gallium nitride, Sapphire, Phonons, Anisotropy, Raman scattering, Raman spectroscopy, Ellipsometry, Astatine, Optical components, Polarization

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Proceedings Article | 1 July 1998 Paper

Optical studies of the internal electric field distributions, crystal defects, and detector performance of CdZnTe radiation detectors

H. Walter Yao, Ralph James, Edwin Lee, Richard Olsen, Haim Hermon, Robert Anderson

Proceedings Volume 3446, (1998) https://doi.org/10.1117/12.312889

KEYWORDS: Sensors, Crystals, Electric field sensors, Electro optics, Crystallography, Sensor performance, Electro optical modeling, Linear polarizers, Semiconductors, Dielectrics

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Proceedings Article | 7 July 1997 Paper

Optical characterization of the internal electric field distribution under bias of CdZnTe radiation detectors

H. Walter Yao, Richard Anderson, Ralph James

Proceedings Volume 3115, (1997) https://doi.org/10.1117/12.277705

KEYWORDS: Sensors, Electric field sensors, Crystals, Electro optics, Electro optical modeling, Polarizers, Charge-coupled devices, CCD image sensors, Radiation effects, Linear polarizers

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Proceedings Article | 1 July 1992 Paper

In-situ and ex-situ ellipsometric characterization for semiconductor technology (Invited Paper)

John Woollam, Paul Snyder, H. Walter Yao, Blaine Johs

Proceedings Volume 1678, (1992) https://doi.org/10.1117/12.60459

KEYWORDS: Ellipsometry, Silicon, Dielectrics, Oscillators, Semiconductors, Crystals, Refraction, Silicon films, Data modeling, Oxides

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The ellipsometric technique has been around since the end of the last century. However, until the introduction of computers in the 1960s mainly nulling techniques were used. These were accurate, but extremely slow, and data analysis capabilities were limited. The use of personal computers permits rapid data acquisition and analysis. Thus the emphasis is now on ellipsometry for materials research and analysis. Ellipsometry is a unique tool in that it is totally non-destructive and can be performed in any ambient, including air, vacuum, high pressure, or liquid. In ellipsometry a polarized, collimated beam of monochromatic light is reflected at a preselected angle of incidence from the surface of a material, and the polarization state of the reflected beam is determined.1'2 For each wavelength and angle of incidence, one pair of numbers is obtained. These can be used to determine at most two materials parameters; such as the real and imaginary parts of the complex dielectric functions. Frequently, however, two or more variables are correlated and cannot be uniquely determined. This is an important caveat for ellipsometry: one always obtains numbers from the experiment, but they may not be correct. It is extremely important for the user to understand the basis of regression analysis, and the possibility for correlated variables when using ellipsometry for any new materials system.3 To minimize this possibility, multiple angles of incidence and wavelength are used to maximize sensitivity and uniquely determine parameter values. In general, ellipsometry determines the real and imaginary part of the optical dielectric function or equivalently the index of refraction and extinction coefficient. For filmed materials systems, one can potentially determine film thickness (with monolayer sensitivity), void fraction (density), alloy fraction, interfacial and/or surface roughness, and other microstructural properties.4 To do these sophisticated levels of microstructural materials analysis requires spectroscopic and variable angle measurements, in order to minimize correlation, increase sensitivity, and maximize total information obtained

SPIE Journal Paper | 1 April 1990

Pulsed laser annealing of GaAs implanted with Se and Si

Andrew Rys, Yanan Shieh, Alvin Compaan, H. Walter Yao, Ajit Bhat

OE, Vol. 29, Issue 04, (April 1990) https://doi.org/10.1117/12.10.1117/12.55603

KEYWORDS: Gallium arsenide, Annealing, Dye lasers, Silicon, Excimer lasers, Pulsed laser operation, Selenium, Raman spectroscopy, Reflectivity, Etching

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