Dr. William Lotshaw Profile

Dr. William Lotshaw

at Aerospace Corp

SPIE Involvement:

Author

Publications (16)

Proceedings Article | 26 February 2018 Presentation + Paper

Compact 1 mJ fiber MOPA for space-based laser-ablation resonant ionization mass spectrometry (LARIMS)

Xiaodong Mu, William Crain, Can Nguyen, Pavel Ionov, Paul Steinvurzel, Yaniv Dotan, Petras Karuza, William Lotshaw, Todd Rose, Steven Beck, F. Scott Anderson

Proceedings Volume 10512, 1051211 (2018) https://doi.org/10.1117/12.2295454

KEYWORDS: Pulsed laser operation, Ionization, Fiber lasers, Modulators, Fiber amplifiers, Switches, Laser ablation

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Proceedings Article | 8 May 2017 Paper

Modeling and spectroscopy of carrier relaxation in semiconductor optoelectronics

A. Scofield, A. Hudson, B. Liang, B. Juang, D. Huffaker, W. Lotshaw

Proceedings Volume 10193, 101930C (2017) https://doi.org/10.1117/12.2262807

KEYWORDS: Optoelectronic devices, Carrier dynamics, Luminescence, Optoelectronics, Time resolved spectroscopy, Gallium arsenide, Aluminum, Gallium antimonide, Doping, Spectroscopy, Excitons, Data modeling, Semiconductor optoelectronics

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Proceedings Article | 13 May 2016 Paper

Spectroscopic diagnostics of defect and interface effects on carrier dynamics in semiconductor optoelectronics

A. Scofield, A. Hudson, B. Liang, N. Wells, D. Huffaker, W. Lotshaw

Proceedings Volume 9835, 98350F (2016) https://doi.org/10.1117/12.2224308

KEYWORDS: Diagnostics, Luminescence, Interfaces, Carrier dynamics, Heterojunctions, Gallium arsenide, Aluminum, Metalorganic chemical vapor deposition, Spectroscopy, Temperature metrology

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Proceedings Article | 4 March 2016 Paper

High efficiency fourth-harmonic generation from nanosecond fiber master oscillator power amplifier

Xiaodong Mu, Paul Steinvurzel, Todd Rose, William Lotshaw, Steven Beck, James Clemmons

Proceedings Volume 9731, 973108 (2016) https://doi.org/10.1117/12.2208946

KEYWORDS: Crystals, Second-harmonic generation, Laser crystals, Nonlinear crystals, Oscillators, Fiber amplifiers, Fiber lasers, Amplifiers, Deep ultraviolet, Ultraviolet radiation

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Proceedings Article | 8 March 2014 Paper

Electrical characteristics of AlGaN-GaN high electron mobility transistors and AlGaN Schottky diodes irradiated with protons

Yongkun Sin, Nathan Presser, Brendan Foran, Stephen LaLumondiere, William Lotshaw, Steven Moss

Proceedings Volume 8986, 89861E (2014) https://doi.org/10.1117/12.2037637

KEYWORDS: Field effect transistors, Diodes, Gallium nitride, Gallium arsenide, Silicon carbide, Reliability, Transmission electron microscopy, Transistors, Semiconducting wafers, Aluminum nitride

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AlGaN-GaN high electron mobility transistors (HEMTs) are most suitable for commercial and military applications requiring high voltage, high power, and high efficiency operation. In recent years, leading AlGaN HEMT manufacturers have reported encouraging reliability of these devices, but their long-term reliability especially in the space environment still remains a major concern. In addition, degradation mechanisms in AlGaN HEMT devices are still not well understood, and a large number of traps and defects present both in the bulk and at the surface lead to undesirable characteristics. Study of reliability and radiation effects of AlGaN-GaN HEMTs is therefore necessary before GaN HEMT technology is successfully employed in satellite communication systems. For the present study, we investigated electrical characteristics of AlGaN-GaN HEMTs and AlGaN Schottky diodes irradiated with protons. We studied two types of MOCVD-grown AlGaN HEMTs on semi-insulating SiC substrates (HEMT-1 and HEMT-2) as well as MOCVD-grown Al_0.27Ga_0.73N Schottky diodes on conducting SiC substrates. Our HEMT-1 structure consisted of a GaN cap, AlGaN/AlN barrier, and 2 μm GaN buffer layers. Our HEMT-2 structure consisting of undoped AlGaN barrier and GaN buffer layers grown on an AlN nucleation layer showed a charge sheet density of ~10¹³/cm² and a Hall mobility of ~1500 cm² /V^.sec. Our HEMT-1 devices had a Pt-Au Schottky gate length of 0.2 μm, a total gate width of 200-400 μm periphery, and SiN_x passivation. Electrical characteristics of AlGaN-GaN HEMTs and AlGaN Schottky diodes were compared before and after they were proton irradiated with different energies and fluences. Current-mode deep level transient spectroscopy (DLTS) and capacitance-mode DLTS were employed to study pre-proton irradiation trap characteristics in the AlGaN-GaN HEMTs and AlGaN Schottky diodes, respectively. Focused ion beam (FIB) was employed to prepare both cross-sectional and plan view TEM samples for defect analysis using a high resolution TEM. In addition, electrical characteristics of GaAs MESFETs used as reference devices were compared before and after they were proton irradiated.

Proceedings Article | 7 March 2014 Paper

Catastrophic degradation in high power multi-mode InGaAs-AlGaAs strained quantum well lasers with intrinsic and irradiation-induced defects

Yongkun Sin, Stephen LaLumondiere, Erica DeIonno, Brendan Foran, Nathan Presser, William Lotshaw, Steven Moss

Proceedings Volume 8965, 896504 (2014) https://doi.org/10.1117/12.2037642

KEYWORDS: Semiconductor lasers, Quantum wells, Transmission electron microscopy, Reliability, Failure analysis, High power lasers, Gallium arsenide, Electroluminescence, Physics, Scanning transmission electron microscopy

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A number of groups have studied reliability and degradation processes in GaAs-based lasers, but none of these studies have yielded a reliability model based on the physics of failure. Unsuccessful development of this model originates from the facts that: (i) defects related phenomena responsible for degradation in GaAs-based lasers are difficult to study due to the lack of suitable non-destructive techniques and (ii) degradation process occurs extremely fast after a long period of latency. Therefore, most of laser diode manufacturers perform accelerated multi-cell lifetests to estimate lifetimes of lasers using an empirical model, but this approach is a concern especially for satellite communication systems where high reliability is required of lasers for long-term duration in the space environment. Since it is a challenge to control defects introduced during the growth of laser structures, we studied degradation processes in broad-area InGaAs-AlGaAs strained quantum well (QW) lasers with intrinsic defects as well as those with defects introduced via proton irradiation. For the present study, we investigated the root causes of catastrophic degradation processes in MOCVD-grown broad-area InGaAs-AlGaAs strained QW lasers using various failure mode analysis techniques. A number of lasers were proton irradiated with different energies and fluences. We also studied GaAs double heterostructure (DH) test samples with different amounts of intrinsic defects introduced during MOCVD growth. These samples were proton irradiated as well to introduce additional defects. Deep level transient spectroscopy (DLTS) and time resolved photoluminescence (TR-PL) techniques were employed to study traps (due to point defects) and non-radiative recombination centers (NRCs) in pre- and poststressed lasers, respectively. These characteristics were compared with those in pre- and post-proton irradiated lasers and DHs to study the role that defects and NRCs play in catastrophic degradation processes. Lastly, we employed focused ion beam (FIB), electron beam induced current (EBIC), and high resolution TEM (HR-TEM) techniques to study dark line defects and crystal defects in both post-aged and post-proton irradiated lasers.

Proceedings Article | 7 March 2014 Paper

Variable temperature carrier dynamics in bulk (In)GaAsNSb materials grown by MOVPE for multi-junction solar cells

Yongkun Sin, Zachary Lingley, Stephen LaLumondiere, Nathan Wells, William Lotshaw, Steven Moss, Tae Wan Kim, Luke Mawst, Thomas Kuech

Proceedings Volume 8981, 89811A (2014) https://doi.org/10.1117/12.2037385

KEYWORDS: Gallium arsenide, Carrier dynamics, Temperature metrology, Multijunction solar cells, Transmission electron microscopy, Annealing, Indium gallium phosphide, Antimony, Germanium, Picosecond phenomena

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Proceedings Article | 25 March 2013 Paper

Investigation of carrier removal from QD TJSCs

Christopher Kerestes, David Forbes, Cory Cress, B. Richards, William Lotshaw, Stephen LaLumondiere, Eli Fernandez, Yong Lin, Paul Sharps, Seth Hubbard

Proceedings Volume 8620, 86200W (2013) https://doi.org/10.1117/12.2005573

KEYWORDS: Solar energy, Gallium arsenide, Solar cells, Temperature metrology, External quantum efficiency, Doping, Interfaces, Superlattices, Indium gallium phosphide, Luminescence

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Proceedings Article | 25 March 2013 Paper

Carrier dynamics in bulk 1eV InGaAsNSb materials and epitaxial lift off GaAs-InAlGaP layers grown by MOVPE for multi-junction solar cells

Yongkun Sin, Stephen LaLumondiere, William Lotshaw, Steven Moss, Tae Wan Kim, Kamran Forghani, Luke Mawst, Thomas Kuech, Rao Tatavarti, Andree Wibowo, Noren Pan

Proceedings Volume 8620, 86201L (2013) https://doi.org/10.1117/12.2001528

KEYWORDS: Epitaxial lateral overgrowth, Gallium arsenide, Carrier dynamics, Picosecond phenomena, Antimony, Multijunction solar cells, Solar cells, Zinc, Electroluminescence, Annealing

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III-V multi-junction solar cells are based on a triple-junction design that consists of an InGaP top junction, a GaAs middle junction, and a bottom junction that employs either a 1eV material grown on the GaAs substrate or InGaAs grown on the Ge substrate. The most promising 1 eV material that is currently under extensive investigation is bulk dilute nitride such as InGaAsN(Sb) lattice matched to GaAs substrates. Both approaches utilizing dilute nitrides and lattice-mismatched InGaAs layers have a potential to achieve high performance triple-junction solar cells. In addition, it will be beneficial for both commercial and space applications if III-V triple-junction solar cells can significantly reduce weight and can be manufactured cost effectively while maintaining high efficiency. The most attractive approach to achieve these goals is to employ full-wafer epitaxial lift off (ELO) technology, which can eliminate the substrate weight and also enable multiple substrate re-usages. For the present study, we employed time-resolved photoluminescence (TR-PL) techniques to study carrier dynamics in MOVPE-grown bulk dilute nitride layers lattice matched to GaAs substrates, where carrier lifetime measurements are crucial in optimizing MOVPE materials growth. We studied carrier dynamics in InGaAsN(Sb) layers with different amounts of N incorporated. Carrier lifetimes were also measured from InGaAsN(Sb) layers at different stages of post-growth thermal annealing steps. Post-growth annealing yielded significant improvements in carrier lifetimes of InGaAsNSb double hetero-structure (DH) samples compared to InGaAsN DH samples possibly due to the surfactant effect of Sb. In addition, we studied carrier dynamics in MOVPE-grown GaAs-InAl(Ga)P layers grown on GaAs substrates. The structures were grown on top of a thin AlAs release layer, which allowed epitaxial layers grown on top of the AlAs layer to be removed from the substrate. The GaAs layers had various doping densities and thicknesses. We present our TR-PL results from both pre- and post-ELO processed GaAs-InAl(Ga)P samples.

Proceedings Article | 4 March 2013 Paper

Traps and defects in pre- and post-proton irradiated AlGaN-GaN high electron mobility transistors and AlGaN Schottky diodes

Yongkun Sin, Brendan Foran, Nathan Presser, Stephen LaLumondiere, William Lotshaw, Steven Moss

Proceedings Volume 8625, 86250Z (2013) https://doi.org/10.1117/12.2001526

KEYWORDS: Field effect transistors, Diodes, Gallium nitride, Reliability, Silicon carbide, Transmission electron microscopy, Neodymium, Transistors, Semiconducting wafers, Aluminum nitride

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Proceedings Article | 4 March 2013 Paper

Catastrophic degradation in high-power InGaAs-AlGaAs strained quantum well lasers and InAs-GaAs quantum dot lasers

Yongkun Sin, Stephen LaLumondiere, Brendan Foran, Neil Ives, Nathan Presser, William Lotshaw, Steven Moss

Proceedings Volume 8640, 86401G (2013) https://doi.org/10.1117/12.2006624

KEYWORDS: Quantum wells, Semiconductor lasers, Laser applications, High power lasers, Fiber lasers, Reliability, Transmission electron microscopy, Astatine, Electroluminescence, Indium gallium arsenide

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Proceedings Article | 26 February 2013 Paper

Catastrophic optical bulk damage (COBD) processes in aged and proton-irradiated high power InGaAs-AlGaAs strained quantum well lasers

Yongkun Sin, Stephen LaLumondiere, Brendan Foran, William Lotshaw, Steven Moss

Proceedings Volume 8605, 86050M (2013) https://doi.org/10.1117/12.2001530

KEYWORDS: Quantum wells, Reliability, Semiconductor lasers, Lab on a chip, High power lasers, Electroluminescence, Laser applications, Laser optics, Failure analysis, Transmission electron microscopy

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Proceedings Article | 28 February 2012 Paper

Carrier dynamics and defects in MOVPE-grown bulk InGaAs layers with metamorphic InGaAs and InGaPSb buffer layers for solar cells

Yongkun Sin, Stephen LaLumondiere, Brendan Foran, William Lotshaw, Steven Moss, Tae Wan Kim, Peter Dudley, Jeremy Kirch, Steven Ruder, Luke Mawst, Thomas Kuech

Proceedings Volume 8255, 825516 (2012) https://doi.org/10.1117/12.906424

KEYWORDS: Indium gallium arsenide, Chemical mechanical planarization, Gallium arsenide, Transmission electron microscopy, Surface roughness, Carrier dynamics, Solar cells, Indium gallium phosphide, Luminescence, Antimony

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Proceedings Article | 22 February 2012 Paper

Characteristics of bulk InGaAsN and InGaAsSbN materials grown by metal organic vapor phase epitaxy (MOVPE) for solar cell application

TaeWan Kim, Toby Garrod, Kangho Kim, Jaejin Lee, Luke Mawst, T. Kuech, S. LaLumondiere, Y. Sin, W. Lotshaw, S. Moss

Proceedings Volume 8256, 82561D (2012) https://doi.org/10.1117/12.906961

KEYWORDS: Solar cells, Carbon, Gallium arsenide, Picosecond phenomena, Metals, Annealing, Antimony, External quantum efficiency, Vapor phase epitaxy, Antireflective coatings

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Proceedings Article | 9 February 2012 Paper

Physics of failure investigation in high-power broad-area InGaAs-AlGaAs strained quantum well lasers

Yongkun Sin, Stephen LaLumondiere, Nathan Presser, Brendan Foran, Neil Ives, William Lotshaw, Steven Moss

Proceedings Volume 8241, 824116 (2012) https://doi.org/10.1117/12.906436

KEYWORDS: Quantum wells, Semiconductor lasers, High power lasers, Transmission electron microscopy, Refractive index, Physics, Laser optics, Failure analysis, Reliability, Absorption

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Proceedings Article | 21 February 2011 Paper

Carrier dynamics in MOVPE-grown bulk dilute nitride materials for multi-junction solar cells

Yongkun Sin, Stephen LaLumondiere, Toby Garrod, Tae Wan Kim, Jeremy Kirch, Luke Mawst, William Lotshaw, Steven Moss

Proceedings Volume 7933, 79330H (2011) https://doi.org/10.1117/12.873894

KEYWORDS: Picosecond phenomena, Annealing, Antimony, Gallium arsenide, Carrier dynamics, Carbon, Multijunction solar cells, Doping, Streak cameras, Diffusion

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Showing 5 of 16 publications

Conference Committee Involvement (3)

Ultrafast Bandgap Photonics III

16 April 2018 | Orlando, FL, United States

Ultrafast Bandgap Photonics II

10 April 2017 | Anaheim, CA, United States

Ultrafast Bandgap Photonics

18 April 2016 | Baltimore, MD, United States

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