Dr. Charles J. Collins Profile

Dr. Charles J. Collins

Director, Advanced Technology Group at Luminex Corp

SPIE Involvement:

Author

Proceedings Article | 2 October 2008 Paper

Low cost LED-based xMAP analyzer for multiplexed diagnosis and environmental detection of biological agents

Charles Collins, Amy Altman, Wayne Roth, John Carrano

Proceedings Volume 7116, 711605 (2008) https://doi.org/10.1117/12.803576

KEYWORDS: Light emitting diodes, Diagnostics, Magnetism, Biological research, Charge-coupled devices, Statistical analysis, Luminescence, Multiplexing, Imaging systems, Viruses

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Proceedings Article | 25 March 2005 Paper

Fundamental studies of nanoscale phenomena in ultraviolet photonic materials and devices

Michael Wraback, Gregory Garrett, Anand Sampath, Charles Collins, Sergey Rudin, H. Shen

Proceedings Volume 5732, (2005) https://doi.org/10.1117/12.588010

KEYWORDS: Picosecond phenomena, Aluminum, Gallium, Gallium nitride, Ultraviolet radiation, Electron transport, Sapphire, Light emitting diodes, Semiconductors, Luminescence

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Proceedings Article | 29 December 2004 Paper

AlGaN materials for semiconductor sensors and emitters in 200- to 365-nm range

Alexander Usikov, Elizaveta Shapvalova, Yuri Melnik, Vladimir Ivantsov, Vladimir Dmitriev, Charles Collins, Anand Sampath, Gregory Garrett, Paul Shen, Michael Wraback

Proceedings Volume 5617, (2004) https://doi.org/10.1117/12.578452

KEYWORDS: Gallium nitride, Aluminum nitride, Silicon carbide, Doping, Gallium, Sapphire, Magnesium, Zinc, Ultraviolet radiation, Silicon

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Proceedings Article | 29 December 2004 Paper

Make light, not heat: toward higher efficiency nitride semiconductor ultraviolet optical sources

Michael Wraback, Gregory Garrett, Anand Sampath, Charles Collins, Paul Shen

Proceedings Volume 5617, (2004) https://doi.org/10.1117/12.581202

KEYWORDS: Picosecond phenomena, Gallium nitride, Aluminum, Aluminum nitride, Luminescence, Indium, Gallium, Quantum wells, Semiconductors, Ultraviolet radiation

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We have used subpicosecond time-resolved photoluminescence (TRPL) downconversion techniques to study the interplay of carrier localization and radiative and nonradiative processes in the active regions of light emitting III-nitride semiconductor ultraviolet optical sources, with the goal of identifying potential approaches that will lead to higher radiative efficiency. Comparison of TRPL in (In)AlGaN multiple quantum well active regions indicate that for addition of only 0.01 In content the PL decay time in an InAlGaN MQW is more than double that in an AlGaN MQW designed to emit at the same wavelength (360 nm), thus indicating the importance of indium for improvement of material quality, most likely through the suppression of point defects. This result is further underscored by TRPL data on 320 nm InAlGaN MQW active regions, which exhibit longer PL lifetimes than expected for growth on GaN templates with dislocation densities in the mid-10⁸cm^-2 range. While the PL lifetimes in these InAlGaN MQWs improve for growth on lower dislocation density HVPE bulk GaN substrates, a similar phenomenon is not observed for deposition on nearly dislocation-free bulk AlN substrates, suggesting that defect generation in the MQWs associated with lattice mismatch or AlN surface preparation may play an important role. The pump intensity dependence of the time zero signal and the TRPL decays in the MQWs implies that internal electric field-induced recombination through the barriers and interface states plays an important role in the radiative efficiency of quantum well active regions for c-axis oriented materials and devices. The effect of these internal electric fields can be mitigated through the use of nonpolar MQWs. The combination of more intense time-integrated PL spectra and shorter PL lifetimes with decreasing well width in GaN/AlGaN MQWs grown on a-plane LEO GaN for low pump intensity suggests that the radiative lifetime becomes shorter due to the accompanying increase in exciton binding energy and oscillator strength at smaller well width in these high quality samples. Finally, it is demonstrated that compositional fluctuations in AlGaN active regions grown by plasma-assisted MBE can be employed to create spatial localization that enhances the luminescence efficiency and PL lifetime (300-400 ps) despite high defect density (>10¹⁰cm^-2) by inhibiting movement of carriers to nonradiative sites. Significant enhancement of this phenomenon has been obtained in a DH LED structure grown on a lower defect density (mid-10⁹cm^-2) AlGaN template, with PL lifetime increased by nearly a factor of two, corresponding to a defect density in the mid-10⁷ cm^-2 range, and only a 3.3 times drop in PL intensity when the temperature is raised from 12 K to room temperature, suggesting up to ~ 30% internal quantum efficiency.

Proceedings Article | 14 August 2003 Open Access

Photodetectors: UV to IR

Joe Campbell, Shuling Wang, Xiaoguang Zheng, Xiaowei Li, Ning Li, Feng Ma, Xiaoguang Sun, Charles Collins, A. Beck, B. Yang, Jeffrey Hurst, Rubin Sidhu, Archie Holmes, U. Chowdhury, Michael Wong, Russell Dupuis, Andrew Huntington, Larry Coldren, Zhonghui Chen, Eui-Tae Kim, Anupam Madhukar

Proceedings Volume 5246, (2003) https://doi.org/10.1117/12.511201

KEYWORDS: Avalanche photodetectors, Aluminum, Gallium, Photodetectors, Photodiodes, Gallium arsenide, Ionization, Electrons, Ultraviolet radiation, Quantum dots

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Proceedings Article | 1 July 2003 Paper

Photodetectors: UV to IR

Joe Campbell, Shuling Wang, Xiaoguang Zheng, Xiaowei Li, Ning Li, Feng Ma, Xiaoguang Sun, Charles Collins, A. Beck, B. Yang, Jeffrey Hurst, Rubin Sidhu, Archie Holmes, U. Chowdhury, Michael Wong, Russell Dupuis, Andrew Huntington, Larry Coldren, Zhonghui Chen, Eui-Tae Kim, Anupam Madhukar

Proceedings Volume 4999, (2003) https://doi.org/10.1117/12.482483

KEYWORDS: Avalanche photodetectors, Photodetectors, Ionization, Electrons, Quantum dots, Ultraviolet radiation, Resistance, External quantum efficiency, Avalanche photodiodes, Indium arsenide

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Proceedings Article | 30 May 2003 Paper

Femtosecond optical studies of carrier localization and recombination in III-nitride semiconductors

Michael Wraback, G. Garrett, A. Sampath, C. Collins, Hongen Shen

Proceedings Volume 4992, (2003) https://doi.org/10.1117/12.475715

KEYWORDS: Gallium nitride, Aluminum, Picosecond phenomena, Reflectivity, Luminescence, Semiconductors, Gallium, Sapphire, Ultrafast phenomena, Absorption

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We have used femtosecond time-resolved reflectivity and luminescence downconversion techniques to study carrier relaxation, localization, and recombination in III-nitride semiconductors. Intensity dependent, frequency degenerate pump-probe reflectivity measurements employing near-bandgap excitation provide information about initial carrier localization, subsequent ultrafast heat generation due to nonradiative recombination or trapping in states deep in the bandgap, and photoinduced absorption associated with excitation of carriers from localized states to the bands. These phenomena and their experimental signatures are illustrated for Al_0.25Ga_0.75N and Al_0.4Ga_0.6N samples, in which the photoinduced change in reflectivity ΔR decays faster with decreasing intensity and changes sign, with faster decays for a given intensity in the higher Al content sample. This behavior suggests that in these cases the dynamics are governed by trapping at localized states associated with alloy fluctuations that become deeper and more numerous as the Al content increases. Within this context the sign change and subsequent temporal evolution of ΔR may be indicative of ultrafast heat generation and/or photoinduced absorption, depending upon A1 content. Nondegenerate pump-probe reflectivity experiments designed to separate the electronic contributions of the ΔR decays from the slower thermal components by using a sub-bandgap probe are used to measure carrier lifetime in GaN. Comparison with data obtained from frequency degenerate experiment sunder identical excitation conditions employing a near bandgap probe indicate that in the frequency degenerate case the decay times in ΔR are inflated due to the presence of an additional long-lived component with the same sign as the electronic contribution. The sign and power dependence of this slow decay suggest that it may be associated with screening of a surface electric field by carriers trapped in deep states. In addition, a new technique is presented that employs luminescence downconversion using an ultrashort gating pulse to enable the characterization of UV light emission from III-nitride semiconductors with subpicosecond temporal resolution. This technique also allows one to measure PL rise times and fast components of multiple decays in the subsequent time evolution of the PL intensity. Comparison of luminescence emission intensity and lifetime in GaN and AlGaN with ~0.1 Al content grown homoepitaxially on GaN templates with the same quantities measured in heteroepitaxial layers grown on sapphire indicate significant improvement in the homoepitaxial layers due to reduction in defect density. Fast (<15 ps) initial decays in the AlGaN are attributed to localization in shallow traps associated with alloy fluctuations, with subsequent recombination through gap states.

Proceedings Article | 23 April 2001 Paper

Measurement of carrier transport and dynamics in wide bandgap semiconductors using femtosecond pump-probe techniques

Michael Wraback, Hongen Shen, M. Wood, John Carrano, Charles Collins, Ting Li, Joe Campbell, Christopher Eiting, Damien Lambert, U. Chowdhury, M. Wong, Russell Dupuis, Matthew Schurman, Ian Ferguson

Proceedings Volume 4280, (2001) https://doi.org/10.1117/12.424741

KEYWORDS: Diodes, Electron transport, Gallium nitride, Picosecond phenomena, Femtosecond phenomena, Heterojunctions, Absorption, Interfaces, Scattering, Information operations

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Proceedings Article | 26 October 2000 Paper

AlGaN/GaN ultraviolet photodetectors

Joe Campbell, Ting Li, Shuling Wang, Ariane Beck, Charles Collins, Bo Yang, Damien Lambert, Russell Dupuis, John Carrano, Matthew Schurman, Ian Ferguson

Proceedings Volume 4134, (2000) https://doi.org/10.1117/12.405335

KEYWORDS: Ultraviolet radiation, Gallium nitride, Photodetectors, Photodiodes, Quantum efficiency, Resistance, PIN photodiodes, External quantum efficiency, Aluminum, Diodes

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Proceedings Article | 13 April 2000 Paper

High quantum efficiency AlxGa1-xN/GaN-based ultraviolet p-i-n photodetectors with a recessed window structure

Ting Li, Shuling Wang, Ariane Beck, Charles Collins, Bo Yang, Russell Dupuis, John Carrano, Matthew Schurman, Ian Ferguson, Joe Campbell

Proceedings Volume 3948, (2000) https://doi.org/10.1117/12.382131

KEYWORDS: Quantum efficiency, Gallium nitride, Ultraviolet radiation, Photodetectors, Heterojunctions, Photodiodes, Raster graphics, Reactive ion etching, External quantum efficiency, PIN photodiodes

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Proceedings Article | 13 April 2000 Paper

High-performance GaN/AlGaN-based ultraviolet photodetectors

John Carrano, Ting Li, Charles Collins, Ariane Beck, Shuling Wang, Bo Yang, Damien Lambert, Christopher Eiting, Russell Dupuis, Joe Campbell, Michael Wraback, Hongen Shen, Matthew Schurman, Ian Ferguson

Proceedings Volume 3948, (2000) https://doi.org/10.1117/12.382125

KEYWORDS: Gallium nitride, Ultraviolet radiation, Quantum efficiency, Photodetectors, Photodiodes, PIN photodiodes, Absorption, Avalanche photodetectors, Resistance, Diffusion

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Showing 5 of 11 publications

SPIE Conference Volume | 17 September 2009

Optically Based Biological and Chemical Detection for Defence V

Conference Committee Involvement (4)

Optically Based Biological and Chemical Detection for Defence V

1 September 2009 | Berlin, Germany

Optically Based Biological and Chemical Detection for Defence IV

16 September 2008 | Cardiff, Wales, United Kingdom

Optically Based Biological and Chemical Detection for Defence

18 September 2007 | Florence, Italy

Optically-Based Biological and Chemical Detection for Defence III

11 September 2006 | Stockholm, Sweden

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