Dr. Michael Wraback Profile

Dr. Michael Wraback

Research Physicist at DEVCOM Army Research Lab

SPIE Involvement:

Author

Publications (27)

Proceedings Article | 15 June 2023 Presentation + Paper

Studies of spatial uniformity and jitter in SiC UV SPADs

Anand Sampath, Gregory Garrett, Jonathan Schuster, Jeremy Smith, Michael Derenge, Daniel Habersat, Brenda VanMil, Reza Gandhi, Sergei Dolinsky, Edwin Heilweil, Joshua Bienfang, Enrico Bellotti, Michael Wraback

Proceedings Volume 12512, 1251206 (2023) https://doi.org/10.1117/12.2663387

KEYWORDS: Silicon carbide, Single photon avalanche diodes, Avalanche photodetectors, Temporal resolution, Ultraviolet radiation

Read Abstract +

Proceedings Article | 10 March 2023 Presentation + Paper

Design and optimization of NUV-enhanced 4H-SiC separate-absorption-charge-multiplication avalanche photodiodes

Jonathan Schuster, Anand Sampath, Jeremy Smith, Stephen Kelley, Gregory Garrett, Daniel Habersat, Michael Derenge, Michael Wraback, Dina Bower, Shahid Aslam, Tilak Hewagama

Proceedings Volume 12415, 1241509 (2023) https://doi.org/10.1117/12.2649236

KEYWORDS: Silicon carbide, Avalanche photodetectors, Doping, Absorption, Deep ultraviolet, Ultraviolet radiation, Avalanche photodiodes, Finite-difference time-domain method, Design and modelling, Ionization

Read Abstract +

Proceedings Article | 12 September 2019 Presentation

Investigation of 4H-SiC UV-APDs in Geiger and linear mode operation (Conference Presentation)

Chelsea Haughn, Stephen Kelley, Jeremy Smith, Kimberley Olver, Eric DeCuir, Jerry Cabalo, Michael Wraback, Eugene Chong, Anand Sampath

Proceedings Volume 11126, 1112602 (2019) https://doi.org/10.1117/12.2530822

Read Abstract +

Proceedings Article | 11 June 2013 Paper

Time-resolved photoluminescence study of carrier recombination and transport in type-II superlattice infrared detector materials

Blair Connelly, Grace Metcalfe, Hongen Shen, Michael Wraback

Proceedings Volume 8704, 87040V (2013) https://doi.org/10.1117/12.2016202

KEYWORDS: Superlattices, Luminescence, Mid-IR, Gallium, Long wavelength infrared, Continuous wave operation, Infrared detectors, Temperature metrology, Antimony, Infrared radiation

Read Abstract +

Proceedings Article | 15 October 2012 Paper

Temperature-dependent minority carrier lifetimes of InAs/InAs[sub]1-x[/sub]Sb[sub]x[/sub] type-II superlattices

E. Steenbergen, B. Connelly, G. Metcalfe, H. Shen, M. Wraback, D. Lubyshev, Y. Qiu, J. Fastenau, A. W. Liu, S. Elhamri, O. Cellek, Y.-H. Zhang

Proceedings Volume 8512, 85120L (2012) https://doi.org/10.1117/12.930949

KEYWORDS: Stereolithography, Superlattices, Temperature metrology, Sensors, Long wavelength infrared, Astatine, Quantum efficiency, Infrared detectors, Electrons, Semiconductors

Read Abstract +

Proceedings Article | 25 May 2012 Paper

III-V nitride semiconductors for solar hydrogen production

Vijay Parameshwaran, Chad Gallinat, Ryan Enck, Anand Sampath, Paul Shen, Tevye Kuykendall, Shaul Aloni, Michael Wraback, Bruce Clemens

Proceedings Volume 8377, 83770B (2012) https://doi.org/10.1117/12.925200

KEYWORDS: Semiconductors, Indium gallium nitride, Electrodes, Silicon, Gallium nitride, Photons, Gallium, Hydrogen, Absorption, Semiconductor materials

Read Abstract +

Proceedings Article | 19 May 2012 Paper

III-nitride/SiC avalanche photodetectors for enabling compact biological agent identification and detection

A. Sampath, R. Enck, C. Gallinat, H. Shen, M. Wraback, Q. Zhou, D. McIntosh, J. Campbell

Proceedings Volume 8376, 83760O (2012) https://doi.org/10.1117/12.918866

KEYWORDS: Silicon carbide, Gallium nitride, Avalanche photodetectors, Absorption, Interfaces, Polarization, Sensors, Quantum efficiency, Aluminum nitride, Biological detection systems

Read Abstract +

Proceedings Article | 9 May 2012 Paper

Terahertz polarimetry based on metamaterial devices

Grace Metcalfe, Michael Wraback, Andrew Strikwerda, Kebin Fan, Xin Zhang, Richard Averitt

Proceedings Volume 8363, 83630O (2012) https://doi.org/10.1117/12.918654

KEYWORDS: Terahertz radiation, Metamaterials, Polarimetry, Wave plates, Polarization, Absorption, Spectroscopes, Solids, Spectroscopy, Atmospheric modeling

Read Abstract +

Proceedings Article | 16 September 2011 Paper

Study of recombination mechanisms limiting the performance of Sb-based III-V type II superlattices for infrared detectors

Blair Connelly, Grace Metcalfe, Hongen Shen, Michael Wraback

Proceedings Volume 8155, 81550L (2011) https://doi.org/10.1117/12.893964

KEYWORDS: Doping, Superlattices, Luminescence, Interfaces, Gallium antimonide, Long wavelength infrared, Sensors, Indium arsenide, Temperature metrology, Infrared radiation

Read Abstract +

Proceedings Article | 22 February 2008 Paper

Effect of interface polarization charge on the performance of nitride semiconductor light emitting diodes

Hongen Shen, Meredith Reed, Eric Readinger, Michael Wraback

Proceedings Volume 6889, 688905 (2008) https://doi.org/10.1117/12.773871

KEYWORDS: Polarization, Light emitting diodes, Heterojunctions, Interfaces, Quantum wells, Bismuth, Semiconductors, Electron holes, Gallium, Field effect transistors

Read Abstract +

Proceedings Article | 4 May 2007 Paper

A high resolution terahertz spectrometer for chemical detection

Alexander Majewski, Rene Abreu, Michael Wraback

Proceedings Volume 6549, 65490B (2007) https://doi.org/10.1117/12.719485

KEYWORDS: Spectroscopy, Terahertz radiation, Absorption, Laser stabilization, Control systems, Signal to noise ratio, Chemical detection, Toxic industrial chemicals, Heterodyning, Detection and tracking algorithms

Read Abstract +

Proceedings Article | 8 February 2007 Paper

Enhanced luminescence from AlxGa1-xN/AlyGa1-yN quantum wells grown by gas source molecular beam epitaxy with ammonia

Sergey Nikishin, Boris Borisov, Gregory Garrett, Wendy Sarney, Anand Sampath, Hongen Shen, Michael Wraback, Mark Holtz

Proceedings Volume 6473, 647306 (2007) https://doi.org/10.1117/12.701394

KEYWORDS: Gallium, Aluminum, Quantum wells, Luminescence, Quantum dots, Aluminum nitride, Molecular beam epitaxy, Transmission electron microscopy, Light emitting diodes, Picosecond phenomena

Read Abstract +

Proceedings Article | 2 February 2007 Paper

Optimization of nanoscale phenomena in AlGaN for improved UV emitters

M. Wraback, G. Garrett, A. Sampath, H. Shen

Proceedings Volume 6479, 64791H (2007) https://doi.org/10.1117/12.699181

KEYWORDS: Excitons, Picosecond phenomena, Luminescence, Ultraviolet radiation, Light emitting diodes, Internal quantum efficiency, Gallium nitride, Temperature metrology, Diffusion, Aluminum

Read Abstract +

Proceedings Article | 13 October 2006 Paper

Device challenges for biodetection

M. Wraback, M. Reed, G. Garrett, A. Sampath, H. Shen

Proceedings Volume 6398, 63980W (2006) https://doi.org/10.1117/12.693124

KEYWORDS: Gallium nitride, Picosecond phenomena, Light emitting diodes, Luminescence, Avalanche photodetectors, Ultraviolet radiation, Semiconductors, Sensors, Ultraviolet light emitting diodes, Avalanche photodiodes

Read Abstract +

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

Read Abstract +

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

Read Abstract +

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 | 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

Read Abstract +

Proceedings Article | 25 July 2003 Paper

Effect of carrier screening on InGaAs MSM detector

Hongen Shen, Keith Aliberti, Gerard Dang, Michael Wraback

Proceedings Volume 4986, (2003) https://doi.org/10.1117/12.480857

KEYWORDS: Indium gallium arsenide, Photodetectors, Sensors, Diodes, Solids, Picosecond phenomena, Energy efficiency, Semiconductors, Gallium arsenide, Absorption

Read Abstract +

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

Read Abstract +

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 | 12 June 2002 Paper

Use of photodetectors for the measurement of carrier velocities in wide-bandgap semiconductors

Michael Wraback, Hongen Shen, Sergey Rudin

Proceedings Volume 4646, (2002) https://doi.org/10.1117/12.470507

KEYWORDS: Diodes, Gallium nitride, Electron transport, Picosecond phenomena, Heterojunctions, Monte Carlo methods, Velocity measurements, Resistance, Photodetectors, Femtosecond phenomena

Read Abstract +

We present an optically-detected time-of-flight technique with femtosecond resolution that monitors the change in the electroabsorption due to charge transport in a p-i-n diode, and show how it may be used to determine the electron transit time, velocity-field characteristic, and transient electron velocity overshoot in GaN at room temperature. In a GaN homojunction p-i-n diode, the peak electron velocity of 1.9x10⁷ cm/s , corresponding to a transit time of ~2.5 ps across the 0.53 micrometers depletion region, is attained at ~ 225 kV/cm. The steady-state velocity-field characteristic is in qualitative agreement with theoretical calculations. A measurement of the high field transient electron velocity overshoot was also performed using a semi-transparent p-contact AlGaN/GaN heterojunction p-i-n diode. Transient electron velocity overshoot is observed at fields as low as ~100 kV/cm, with the peak transient electron velocity becoming larger with increasing electric field until a maximum of 7.25x10⁷ cm/s is observed within the first 200 fs after photoexcitation at a field of 320 kV/cm. At higher fields, the measurement of the peak velocity is limited by the 80 fs duration of the pulses, but the increase in transit time with increasing field suggests the onset of negative differential resistance. Theoretical Monte Carlo calculations incorporating a GaN full-zone band structure show that although the peak steady-state velocity occurs at ~200 kV/cm, the ensuing negative differential resistance region of the velocity-field curve is not initially associated with intervalley transfer, as the majority of electrons do not attain sufficient energy to effect this transfer until they are subjected to much higher fields (>325kV/cm). Insight into this behavior can be gleaned from the band nonparabolicity deduced from the constant energy surfaces in the (Gamma) valley, which shows that the effective mass in the c-direction can be viewed as becoming larger at high k-values. This larger effective mass may play a role in velocity overshoot by reducing the velocity and momentum relaxation time at high k-values in the (Gamma) valley. Theoretical calculations employing a semiclassical transport model in the collisionless regime confirm the importance of this nonparabolicity for the determination of the temporal shape of the transient velocity overshoot curves.

Proceedings Article | 21 May 2002 Paper

Femtosecond studies of fundamental materials issues in III-nitride ultraviolet photodetectors

Michael Wraback, Hongen Shen

Proceedings Volume 4650, (2002) https://doi.org/10.1117/12.467652

KEYWORDS: Aluminum, Gallium, Absorption, Gallium nitride, Picosecond phenomena, Photodetectors, Reflectivity, Carrier dynamics, Ultraviolet radiation, Femtosecond phenomena

Read Abstract +

We have used femtosecond time-resolved optical techniques to study fundamental materials issues in III-nitride semiconductors relevant to the realization of high quality ultraviolet photodetectors. Intensity dependent pump-probe reflectivity and transmission measurements have been employed in the investigation of carrier dynamics in AlGaN alloys with Al content ranging from ~0.15 to 0.4. For the Al_0.15Ga_0.85N sample, the intensity dependence of the (Delta) R decay suggests that at high intensity the shallow traps are saturated and ultrafast nonradiative recombination dominates the carrier dynamics. For the Al_0.25Ga_.75N and Al_0.4Ga_0.6N samples (Delta) R decays faster with decreasing intensity and changes sign. Moreover, the decays are faster for a given in tensity in the higher Al content sample. This behavior suggests that in these cases the dynamics are governed by trapping at localized states that become deeper and more numerous as the Al content increases. Within this context the sign change in (Delta) R in A;_0.4Ga_0.6N may be indicative of the onset of photoinduced absorption associated with the excitation of carriers from the localized states to the bands, which has also been observed in time-resolved transmission measurements. This localization may be associated with alloy fluctuations that broaden the absorption edge of the material and degrade the long-wavelength performance of photodetectors. In addition, time-resolved electroabsorption measurements on an AlGaN/GaN heterojunction p-i-n photodiode have been used to study the transient electron velocity overshoot for transport in the c-direction in wurzite GaN. The velocity overshoot is observed at fields well below the field at which the calculated peak steady-state velocity occurs, and it increases with electric field up to ~320 kV/cm, at which field a peak velocity of 7.25x10⁷ cm/s is attained within the first 200 fs after photoexcitation. These results are consistent with theoretical Monte Carlo calculations incorporating a GaN full-zone band structure, which show that because of band nonparabolicity in the (Gamma) valley the majority of electrons do not attain sufficient energy to effect intervalley transfer until they are subjected to higher fields (>325kV/cm). This behavior may have important implications for avalanche photodiodes, for which electrons are promoted to higher lying bands for participating in the avalanche process.

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

Read Abstract +

Proceedings Article | 13 April 2000 Paper

Ultraviolet detector materials and devices studied by femtosecond nonlinear optical techniques

Michael Wraback, Hongen Shen, Patrick Kung, Manijeh Razeghi, John Carrano, Ting Li, Joe Campbell

Proceedings Volume 3948, (2000) https://doi.org/10.1117/12.382137

KEYWORDS: Gallium nitride, Picosecond phenomena, Absorption, Photons, Femtosecond phenomena, Reflectivity, Sapphire, Ultrafast phenomena, Ultraviolet detectors, Diodes

Read Abstract +

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

Read Abstract +

Proceedings Article | 6 August 1999 Paper

Polarization-sensitive optically addressed light modulators based on excitonic optical nonlinearities in optically anisotropic materials

Michael Wraback, Hongen Shen

Proceedings Volume 3625, (1999) https://doi.org/10.1117/12.356873

KEYWORDS: Polarization, Modulators, Excitons, Absorption, Anisotropy, Picosecond phenomena, Zinc oxide, Nonlinear optics, Modulation, Polarizers

Proceedings Article | 2 June 1994 Paper

Normal incidence multiple quantum well light modulator with exceedingly high contrast ratio

Hongen Shen, Jagadeesh Pamulapati, Michael Wraback, Monica Taysing-Lara, Peter Newman, Mitra Dutta, Haochung Kuo, Yicheng Lu

Proceedings Volume 2145, (1994) https://doi.org/10.1117/12.177136

KEYWORDS: Polarization, Modulators, Quantum wells, Excitons, Photon polarization, Absorption, Phase shift keying, Amplitude modulation, Birefringence, Gallium arsenide

Read Abstract +

Proceedings Article | 26 May 1994 Paper

Optical study of lift-off multiple quantum well thin films under various types of thermally induced in-plane strain

Hongen Shen, Michael Wraback, Jagadeesh Pamulapati, Monica Taysing-Lara, Weimin Zhou, Mitra Dutta, Yu Lu, Haochung Kuo

Proceedings Volume 2141, (1994) https://doi.org/10.1117/12.176853

KEYWORDS: Thin films, Gallium arsenide, Absorption, Quantum wells, Anisotropy, Temperature metrology, Thermography, Glasses, Polarization, Birefringence

Read Abstract +

Showing 5 of 27 publications

Conference Committee Involvement (2)

Quantum Sensing and Nanophotonic Devices VII

24 January 2010 | San Francisco, California, United States

Quantum Sensing and Nanophotonic Devices VI

25 January 2009 | San Jose, California, United States

View contact details

UPDATE YOUR PROFILE

Is this your profile? Update it now.

Sign into your SPIE.org account

Don’t have a profile and want one?

Create an account on SPIE.org

Keywords/Phrases

Search In:

Publication Years